Expertise in airway management is critical for administering anesthesia safely. Difficult airway management is defined as the clinical situation in which conventionally trained anesthesia personnel experience difficulty with ventilation via a face mask or endotracheal intubation or both. (1) Difficult or failed airway management is a major factor in anesthesia-related morbidity (dental damage, aspiration of gastric contents, airway trauma, unanticipated surgical airway, anoxic brain injury, cardiopulmonary arrest) and fatality.(1,2) Competence in airway management requires (1) knowledge of the anatomy and physiology of the airway, (2) ability to evaluate the patient’s history that is relevant to airway management, (3) physical examination of anatomic features correlating with difficult airway management, (4) skill with the many devices for airway management, and (5) appropriate application of the American Society of Anesthesiologists (ASA) algorithm for difficult airway management (Fig.1). (1)

The editors and publisher would like to thank Dr. Robin A. Stack-house for contributing to this chapter in the previous edition of this work. It has served as the foundation for the current chapter.

Nose

Air is warmed and humidified as it passes through the nares during normal breathing. Resistance to airflow through the nasal passages is twice that through the mouth and accounts for approximately 50% to 75% of total airway resistance.(3) The majority of the sensory innervation of the nasal cavity is derived from the ethmoidal branch of the ophthalmic nerve and branches of the maxillary division of the trigeminal nerve from the sphenopalatine ganglion (Fig.2). (3,4)

Mouth and Pharynx

Branches of the maxillary division of the trigeminal nerve that innervate the mouth include the greater and lesser palatine nerves and the lingual nerve. The greater and lesser palatine nerves provide most of the sensation to the hard palate, soft palate, and the tonsils, and the lingual nerve provides sensation to the anterior two thirds of the tongue. The posterior third of the tongue, the soft palate, and the oropharynx are innervated by the glossopharyngeal nerve (cranial nerve IX) (Figs.3 and 4). (5)

The pharynx connects the nasal and oral cavities to the larynx and esophagus. The pharynx is composed of the nasopharynx, oropharynx, and hypopharynx. The nasopharynx is separated from the oropharynx by the soft palate. The epiglottis demarcates the border between the oropharynx and the hypopharynx. The internal branch of the superior laryngeal nerve, which is a branch of cranial nerve X (vagus), provides sensory innervation to the hypopharynx, including the base of the tongue, posterior surface of the epiglottis, aryepiglottic folds, and arytenoids (Fig.5). (6)

Airway resistance may be increased by prominent lymphoid tissue in the nasopharynx. The tongue is the predominant cause of airway resistance in the oropharynx. Obstruction by the tongue is increased by relaxation of the genioglossus muscle during anesthesia.

Larynx

The adult larynx is located at the level of the third to sixth cervical vertebrae. (7) One of its primary functions is to protect the distal airways by closing when stimulated to prevent aspiration. This protective mechanism, when exaggerated, becomes laryngospasm. The larynx is composed of a cartilaginous framework connected by fascia, muscles, and ligaments. There are three unpaired and three paired cartilages. The unpaired cartilages are the epiglottis, thyroid, and cricoid, and the paired cartilages are the arytenoids, corniculates, and cuneiforms. The cricoid cartilage is shaped like a signet ring, wider in the cephalocaudal dimension posteriorly, and is the only cartilage that is a full ring structure. The vocal cords are formed by the thyroarytenoid ligaments and are the narrowest portion of the adult airway. An understanding of the motor and sensory innervation of the laryngeal structures is important for performing anesthesia of the upper airway (Table 1).

Trachea

The trachea extends from the larynx to the carina, which overlies the fifth thoracic vertebra. An adult trachea is 10 to 15 cm long and supported by 16 to 20 horseshoe-shaped cartilages. The sensory innervation of the trachea is from the recurrent laryngeal nerve, a branch of cranial nerve X (vagus).

History and Anatomic Examination

A comprehensive assessment of the airway should consist of a history of the patient’s airway experiences, review of previous anesthetic and medical records, physical examination, and additional evaluations when necessary. (1) The airway history should be evaluated to determine whether there are any medical, surgical, or anesthetic factors that have implications for airway management, including the risk of aspiration of gastric contents. (1,8) Various congenital and acquired disease states have a correlation with difficult airway management (Tables 2 and 3). Patients who have had a previous problem with airway management should have been informed of the problem. Patients’ difficult airway specifics can be documented by a written letter, an alert or note in the medical record, a notification bracelet such as the medical alert system or equivalent device, or by discussion with the patient’s surgeon, primary care physician, family member, or patient representative. The previous anesthetic record should contain a description of the airway difficulties (i.e., difficult laryngeal mask, supraglottic airway or intubation, or both), what airway management techniques were used, and whether they were successful. (1)

Physical Examination Findings

Physical examination of the airway should evaluate multiple features to detect predictors of a difficult airway (Table 4). Physical examination features and other bedside tests have a low sensitivity and specificity for any single test and its implications for difficult airway management. (9,10) Combining tests and other risk factors correlates with some improvement in the accuracy of predicting a difficult airway. (10,11) Examination of the oropharyngeal space, submandibular space and compliance, and cervical spine mobility as well as evaluation of patients’ body habitus can help to identify increased risk of difficult airway management. Recognition of patients who may be a difficult laryngoscopy and intubation as well as difficult mask, supraglottic airway placement, or surgical airway can highlight the need for further evaluation and preparation. (1)

Oropharyngeal Space

The Mallampati test is used to evaluate the oropharyngeal space and its predicted effect on ease of direct laryngoscopy and endotracheal intubation. (12) There is a correlation between a modified Mallampati score of 3 and 4 with difficult laryngoscopy. The airway is classified according to what structures are visible. For the modified Mallampati score, the observer should be at eye level with the patient holding the head in a neutral position, opening the mouth maximally, and protruding the tongue without phonating (Fig.6). (13)

Class I: The soft palate, fauces, uvula, and tonsillar pillars are visible.                                                                                                                                  Class II: The soft palate, fauces, and uvula are visible.                                                                                                                                                  Class III: The soft palate and base of the uvula are visible.                                                                                                                                              Class IV: The soft palate is not visible.

In conjunction with the Mallampati examination, the interincisor gap, the size and position of the maxillary and mandibular teeth, and the conformation of the palate can be assessed. (1) An interincisor gap of less than 3 to 4.5 cm correlates with difficulty achieving a line of view on direct laryngoscopy. (11) Maxillary prominence or a receding mandible also correlate with a poor laryngoscopic view. Overbite results in a reduction in the effective interincisor gap when the patient’s head and neck are optimally positioned for direct laryngoscopy. A narrow or highly arched palate is another airway examination finding that is associated with a potential difficult airway. (1)

The submandibular space is the area into which the soft tissues of the pharynx must be displaced to obtain a line of vision during direct laryngoscopy. Anything that limits the submandibular space or compliance of the tissue will decrease the amount of anterior displacement that can be achieved. Micrognathia limits the pharyngeal space (tongue positioned more posterior) and the space in which the soft tissues need to be displaced. This causes the glottic structures to be anterior to the line of vision during direct laryngoscopy.

The extent of an individuals’ ability to prognath the mandible is another correlate of the visualization of glottic structures on direct laryngoscopy. The upper lip bite test (ULBT) classification system is as follows (class III is associated with a difficult intubation): (11)

Class I: Lower incisors can bite above the vermilion border of the upper lip.                                                                                                                  Class II: Lower incisors cannot reach vermilion border.                                                                                                                                                   Class III: Lower incisors cannot bite upper lip. (14)

Ludwig’s angina, tumors or masses, radiation scarring, burns, and previous neck surgery are conditions that can decrease submandibular compliance. (1)

Thyromental/Sternomental Distance

A thyromental distance (mentum to thyroid cartilage) less than 6 to 7 cm correlates with a poor laryngoscopic view. This is typically seen in patients with a receding mandible or a short neck, which creates a more acute angle between the oral and pharyngeal axes and limits the ability to bring them into alignment. This distance is often estimated in fingerbreadths. Three ordinary fingerbreadths approximate this distance. If the sternomental distance is used, it should measure more than 12.5 to 13.5 cm. (9,11)

Atlanto-Occipital Extension/Cervical Spine Mobility

Extension of the head on the atlanto-occipital joint is important for aligning the oral and pharyngeal axes to obtain a line of vision during direct laryngoscopy (Fig. 7). Flexion of the lower neck, by elevating the head approximately 10 cm, aligns the laryngeal and pharyngeal axes. These maneuvers place the head in the “sniffing” position and bring the three axes into optimal alignment. Atlanto-occipital extension is quantified by the angle traversed by the occlusal surface of the maxillary teeth when the head is fully extended from the neutral position. More than 30% limitation of atlanto-occipital joint extension from a norm of 35 degrees, or less than 80 degrees of extension/flexion, is associated with an increased incidence of difficult endotracheal intubation.

Body Habitus/Other Examination Findings

Obesity, with a body mass index (BMI) greater than 30, is associated with an increased incidence of difficult airway management. (9,17) Proper positioning with a wedge-shaped bolster behind the patient’s back results in a more optimal sniffing position. However, the problem of decreased functional residual capacity (FRC) with subsequent decreased time to arterial oxygen desaturation still persists. Other factors that are associated with difficult airway include increased neck circumference and the presence of a beard. (17,18)

Cricothyroid Membrane

Assessing the ease of performing invasive airway procedures before airway instrumentation has been advocated and is especially important with predicted difficult airway management. (1,19) When routine airway management techniques have failed, ventilation is not adequate, and endotracheal intubation is unsuccessful, invasive airway control through the cricothyroid membrane is indicated; therefore, correctly identifying the cricothyroid membrane can be crucial (see Fig.1). (1) It can be identified by first locating the thyroid cartilage, then sliding the fingers down the neck to the membrane, which lies just below. Alternatively, in patients who do not have a prominent thyroid cartilage, identification of the cricoid cartilage can be achieved by beginning palpation of the neck at the sternal notch and sliding the fingers up the neck until a cartilage that is wider and higher (cricoid cartilage) than those below is felt. The superior border of the cricoid cartilage demarcates the inferior border of the cricothyroid membrane. Predictors of difficulty identifying the cricothyroid membrane include female sex, age less than 8 years, presence of large neck circumference, a displaced airway, and overlying neck malformation. (18)

Ventilation Via a Face Mask

Ventilation via a face mask is a vital airway management tool. Prospectively identifying patients at risk for difficult ventilation via a mask, ensuring the ability to ventilate the patient’s lungs before administering neuro-muscular blocking drugs, and developing proficient face mask ventilation skills are fundamental to the practice of anesthesia.

Independent variables associated with difficult face mask ventilation are (1) age older than 55 years, (2) BMI higher than 30 kg/m2, (3) a beard, (4) lack of teeth, (5) a history of snoring or obstructive sleep apnea, (6) Mallampati class III to IV, (7) history of neck radiation, (8) male sex, (9) limited ability to protrude the mandible, and (10) history of an airway mass or tumor. (19,20) In addition, difficult ventilation via mask can develop after multiple laryngoscopy attempts. The incidence of difficult face mask ventilation ranges from 0.9% to 7.8% (18,20)  and may be due to one or more of the following problems: inadequate mask or supraglottic airway seal, excessive gas leak, or excessive resistance to the ingress or egress of gas. (1) Severe adverse outcomes related to difficult ventilation via a mask include inability to oxygenate, ventilate, prevent aspiration of gastric contents, or a combination of these factors, which can result in hypoxic brain damage or death. (2,20)

Face Mask Characteristics

Face masks are available in a variety of sizes. A properly sized face mask should have the top of mask fit over the bridge of the nose, with the upper border aligned with the pupils and the bottom of the mask should sit between the lower lip and the chin. Most face masks come with a hooked rim around the 15- to 22-mm fitting that attaches to the anesthesia breathing circuit. This rim allows straps to be used to hold the face mask in place when a patient is breathing spontaneously or to improve the seal during face mask ventilation.

Prior to induction of anesthesia, breathing 100% O2 allows for a longer duration of apnea without desatura-tion by increasing oxygen reserves (denitrogenation). A healthy adult, who is not obese, can be apneic for approximately 9 minutes before significant desaturation occurs. This time is primarily dependent on oxygen consumption and the FRC. Obesity, pregnancy, and other conditions that significantly decrease FRC or factors that increase oxygen consumption decrease the time to desaturation (Fig.8) (21).

Several techniques of preoxygenation exist with the goal of achieving an end-tidal oxygen level above 90%. Three minutes of tidal volume breathing of 100% O2 is superior to four deep breaths in 30 seconds. Eight deep breaths in 60 seconds are equivalent to breathing 100% oxygen for 3 minutes. (22) Preoxygenation in a 25-degree head-up position in obese patients can increase the time to desaturation by decreasing atelectasis and improving ventilation/perfusion matching.(22,23) In addition, preoxygenation with noninvasive positive-pressure ventilation followed by a recruitment maneuver immediately after endotracheal intubation in obese patients can preserve lung volumes and oxygenation better than preoxygenation alone (24).

After induction of anesthesia, the face mask should be held to the patient’s face with the fingers of the anesthesia provider’s left hand lifting the mandible (chin lift, jaw thrust) to the face mask. Pressure on the submandibular soft tissue should be avoided because it can cause airway obstruction. The anesthesia provider’s left thumb and index finger apply counterpressure on the face mask. Anterior pressure on the angle of the mandible (jaw thrust), atlanto-occipital joint extension, and chin lift combine to maximize the pharyngeal space. Differential application of pressure with individual fingers can improve the seal attained with the face mask. The anesthesia provider’s right hand is used to generate positive pressure by squeezing the reservoir bag of the anesthesia breathing circuit. Ventilating pressure should be less than 20 cm H2O to avoid insufflation of the stomach.

Managing Inadequate Ventilation Via a Mask

Signs of inadequate mask ventilation include absent or minimal chest rise, absent or inadequate breath sounds, cyanosis, gastric air entry, decreasing or inadequate oxygen saturation, absent or inadequate exhaled carbon dioxide, and hemodynamic changes associated with hypoxemia or hypercarbia, or both. (1)

Inadequate face mask ventilation is usually due to decreased compliance and increased resistance. An oral or nasal airway may help to generate sufficient positive pressure for adequate ventilation with the anesthesia breathing circuit. Oral and nasal airways are designed to create an air passage by displacing the tongue from the posterior pharyngeal wall. Aligning the airway device with the patient’s profile and approximating the anatomic path that it will take can be used to estimate the appropriate size. The distal tip of the oral and nasal airway should be at the angle of the mandible when the proximal end is aligned with the mouth or the nose, respectively. An oral airway may generate a gag reflex or cause laryngospasm in an awake or lightly anesthetized patient. Nasal airways are better tolerated during lighter levels of anesthesia, but are relatively contraindicated in patients who have coagulation or platelet abnormalities, are pregnant, or have basilar skull fractures.

Presence of a beard or lack of teeth may result in inadequate seal between the patient’s face and the mask making it difficult to deliver positive pressure. If the patient is amenable, shaving or trimming a beard can improve face mask seal. If a patient’s dentures are well adhered, allowing them to be left in place or use of an oral airway can improve face mask seal in edentulous patients.

If oral and nasal airways do not optimize ventilation with a face mask, a two-handed face mask technique should be utilized. The anesthesia provider uses the right hand to mirror the hand position of the left to improve face mask seal and jaw thrust. A second person can assist by ventilating the patient with the reservoir bag. In spite of corrective measures, if difficult or impossible face mask ventilation continues, intubation or placement of a supraglottic airway should be attempted. (1)

Supraglottic airway devices have become invaluable for routine and difficult airway management. For elective airway management, advantages over endotracheal intubation include the following: placement quickly and without the use of laryngoscope, less hemodynamic changes with insertion and removal, less coughing and bucking with removal, no need for muscle relaxants, preserved laryngeal competence and mucociliary function, and less laryngeal trauma. (25) In the difficult airway scenario, they can be a lifesaving tool for oxygenation and ventilation as well as a conduit for intubation. Many of the factors that result in difficult mask ventilation and intubation do not overlap with those that influence supraglottic airway success. Therefore, when other oxygenation or ventilation techniques have failed, a supraglottic airway device may still succeed. (26) Difficult supraglottic airway placement or failure has been associated with small mouth opening, supra- or extraglottic disease, fixed cervical spine deformity, use of cricoid pressure, poor dentition or large incisors, male sex, surgical table rotation, and increased BMI. (18,27) The incidence of difficult supraglottic airway placement, indicated by inability of an anesthesiologist to provide adequate ventilation is 1.1%. (27)

Some contraindications for using supraglottic airway devices are as follows: patients at risk for regurgitation of gastric contents, nonsupine position, obesity, pregnant patients, long surgical time, and intra-abdominal or airway procedures. (25) Although there have been numerous studies of patients in these categories in which supraglottic airways have been successfully used, one must consider the risk versus benefit of use in these situations. After placement of a supraglottic airway device, it is important to confirm correct positioning by observing endtidal CO2 and auscultation of breath sounds.

Reported complications of laryngeal mask airway (LMA) use in difficult airway patients include broncho-spasm, postoperative swallowing difficulties, respiratory obstruction, laryngeal nerve injury, edema, and hypoglossal nerve paralysis.(1) Aspiration remains a concern with supraglottic airway placement and its risk increases with gastric inflation, high airway pressures, and poor supraglottic airway positioning over the glottis. (8) There are many different types of supraglottic airway devices in single-use and reusable forms, including intubating supraglottic airways and supraglottic airways allowing gastric decompression. Supraglottic airway devices are sized according to the patient’s weight, and sizes vary by manufacturer. Selected devices are detailed next.

Laryngeal Mask Airway

LMA Classic and Unique

The original LMA, the LMA Classic, is reusable, and the LMA Unique is the comparable single-use device. These LMAs consist of a flexible shaft connected to a silicone rubber mask (Classic) or polyvinylchloride (Unique) that seals with the airway in the hypopharynx (Fig.9). The distal tip of the cuff should be against the upper esophageal sphincter (cricopharyngeus muscle), the lateral edges rest in the piriform sinuses, and the proximal end seats under the base of the tongue. Before placement, the cuff should be deflated, the device should be lubricated, and the head should be positioned in the sniffing position. These LMAs are designed to be inserted by holding the shaft between the index finger and thumb with the tip of the index finger at the junction of the mask and the tube. Upward pressure against the hard palate is applied as they are advanced toward the larynx until resistance is felt. Intubation through these devices can be facilitated by use of an intubation catheter and a fiberoptic bronchoscope (see later section regarding Aintree Intubation Catheter [AIC]). The LMA Classic and LMA Unique are available in sizes for infant, pediatric, and adult patients.

LMA Fastrach

The LMA Fastrach (intubating LMA, ILMA) was designed to obviate the problems encountered when attempting to blindly intubate the trachea through the LMA Classic. The ILMA is used with a specialized endotracheal tube that exits the laryngeal mask at a different angle than a standard endotracheal tube and results in better alignment with the airway. It is also available in a single-use version.

LMA ProSeal/LMA Supreme

The reusable LMA ProSeal and single-use LMA Supreme are modifications of the LMA Classic (Fig.10). Their cuffs are modified to extend onto the posterior surface of the mask, which results in an improved airway seal without increasing mucosal pressure. This allows for ventilation with higher airway pressures. They both contain a second lumen that opens at the distal tip of the mask to act as an esophageal vent to keep gases and fluid separate from the airway and facilitate placement of an orogastric tube. This is designed to decrease the risk of regurgitation and aspiration of gastric contents. In addition, placement of an orogastric tube can help confirm proper placement of these devices. The LMA ProSeal and Supreme also have built in bite blocks to decrease the chance of obstruction of the airway tube. The LMA Supreme may be more rapid and easier to insert, has lower cuff pressures, and has higher oropharyngeal leakage pressures when compared to the LMA Classic in patients undergoing surgery. (28) However, when there is difficulty with ventilation, the LMA Classic remains the “gold standard” supraglottic airway device. (26) Intubation through these devices can be achieved by using an intubation catheter and a fiberoptic bronchoscope. Both are available in pediatric and adult sizes.

LMA Flexible

The LMA Flexible has a wire-reinforced, flexible airway tube that allows it to be positioned away from the surgical field while minimizing loss of seal. This can be useful for procedures involving the head and neck. Insertion of the LMA Flexible is more difficult than the LMA Classic.(25) Using a stylet or introducer may help with insertion of this device. It is available as a reusable or single-use device in adult and pediatric sizes.

Air-Q Masked Laryngeal Airways

The Air-Q is a device that can be utilized either as a primary airway or as an intermediary channel for intubation of the trachea. It has an elliptical, inflatable, cuffed mask and a slightly curved airway tube with a detachable connector. Several features serve to aid intubation: a short shaft, no aperture bars within the mask, a detachable connector so that the wide lumen of the shaft can be used for intubation, and a distal airway tube shaped to direct an endotracheal tube toward the larynx.(25) When used as a conduit for intubation, each size of the Air-Q laryngeal mask has a corresponding maximum cuffed endotracheal tube size. After an endotracheal tube is placed, removal of the Air-Q device is aided by a removal stylet. The Air-Q is available in infant, pediatric, and adult sizes as a reusable or single-use airway device. The largest size can be used with up to an 8.5 mm standard endotracheal tube (Fig.11).

I-Gel

The I-Gel is a single-use supraglottic airway device composed of a soft, gel-like, noninflatable cuff. It has a widened, flattened stem with a rigid bite block that acts as a buccal stabilizer to reduce rotation and malpositioning, and a port for gastric tube insertion. It can be a primary airway, but also has a wide bore airway channel that can be used as a conduit for intubation with fiberoptic guidance. (29,30) This supraglottic airway device comes in infant, pediatric, and adult sizes. Adult sizes can accommodate endotracheal tube sizes 6.0 to 8.0 mm.

Esophageal Tracheal Combitube and King Laryngeal Tube

The esophageal tracheal combitube (Combitube) and the King Laryngeal Tube (King LT) are primarily used for emergent airway control in prehospital settings when endotracheal intubation is not possible or feasible. The Combitube is an esophageal and tracheal double-lumen airway, whereas the King LT has a single lumen with a large proximal pharyngeal cuff and a distal esophageal cuff. The blind insertion techniques for these devices require minimal training and no movement of the head or neck. The Combitube is available in adult sizes, and the King LT is available in both pediatric and adult sizes.

A Combitube should be replaced after 8 hours of use owing to pressure the tube exerts on the pharyngeal mucosa. It can be replaced by deflating the oropharyngeal balloon and placing an endotracheal tube anterior or lateral to the Combitube. (31)

Endotracheal intubation may be considered in every patient receiving general anesthesia (Box 1). Orotracheal intubation by direct laryngoscopy in anesthetized patients is routinely chosen unless specific circumstances or the patient’s history and physical examination dictate a different approach. Equipment and drugs used for endotracheal intubation include a properly sized endotracheal tube, laryngoscope, functioning suction catheter, appropriate anesthetic drugs, and equipment for providing positive-pressure ventilation of the lungs with oxygen.

Proper positioning is crucial to successful direct laryngoscopy when alignment of the oral, pharyngeal, and laryngeal axes is necessary for creating a line of vision from the lips to the glottic opening. Elevation of the patient’s head 8 to 10 cm with pads under the occiput (shoulders remaining on the table) and extension of the head at the atlanto-occipital joint serve to align these axes. The height of the operating table should be adjusted so that the patient’s face is near the level of the standing anesthesia provider’s xiphoid cartilage.

The laryngoscopic view obtained is classified according to the Cormack and Lehane score. Grade III or IV views are associated with difficult intubation (Fig.12). (32)

Grade I: Most of the glottis is visible.
Grade II: Only the posterior portion of the glottis is visible.
Grade III: The epiglottis, but no part of the glottis, can be seen.
Grade IV: No airway structures are visualized.

Difficult Airway Management

Difficult laryngoscopy is defined as the inability to visualize any portion of the vocal cords after multiple attempts at direct laryngoscopy. Difficult endotracheal intubation is defined as endotracheal intubation requiring multiple attempts. These occur in about 0.8% to 7.0% of patients in the operating room setting. (9,19) Failed intubation of the trachea occurs in about 1 in 2000 patients in an elective setting. (2,33)

The information obtained through a comprehensive airway assessment should allow development of a plan to manage the patient’s airway. Airway devices have different advantages that make them beneficial in specific situations. Options include direct laryngoscopy, use of alternative airway devices such as video laryngoscopes and endotracheal tube guides, special techniques like awake or asleep fiberoptic endotracheal intubation, or rescue invasive techniques. In patients with anticipated or history of a difficult airway, the following management principles should be considered: (1) awake endotracheal intubation versus intubation after induction of general anesthesia, (2) initial intubation method via noninvasive versus invasive techniques, (3) video laryngoscopy as an initial approach to intubation, and (4) maintaining versus ablating spontaneous ventilation.(1) A patient’s ability to cooperate with airway management should be considered when making an initial plan and a difficult airway cart should be immediately available for management of back-up plans. Intubation attempts should be minimized, and repeat laryngoscopy should only occur when a different tactic is used.(19) The ASA difficult airway algorithm details approaches to alternative strategies of airway management once there is failure of a primary plan (see Fig.1). (1)

Direct Laryngoscopy

The laryngoscope is traditionally held in the anesthesia provider’s left hand near the junction between the handle and blade of the laryngoscope. If not opened by extension of the head, the patient’s mouth may be manually opened by counterpressure of the right thumb on the mandibular teeth and right index finger on the maxillary teeth (“scissoring”). Simultaneously with insertion of the laryngoscope blade, the patient’s lower lip can be rolled away with the anesthesia provider’s left index finger to prevent bruising by the laryngoscope blade. The blade is then inserted on the right side of the patient’s mouth so that the incisor teeth are avoided and the tongue is deflected to the left. Pressure on the teeth or gums must be avoided as the blade is advanced forward and centrally toward the epiglottis. The anesthesia provider’s wrist is held rigid as the laryngoscope is lifted along the axis of the handle to cause anterior displacement of the soft tissues and bring the laryngeal structures into view. The handle should not be rotated as it is lifted to prevent damaging the patient’s upper teeth or gums. Manipulation of the patient’s thyroid cartilage externally on the neck, commonly using backward upward rightward pressure (BURP), may facilitate exposure of the glottic opening. (19)

The endotracheal tube is held in the anesthesia provider’s right hand like a pencil and introduced into the right side of the patient’s mouth with the natural curve directed anteriorly. The endotracheal tube should be advanced toward the glottis from the right side of the mouth as mid-line insertion usually obscures visualization of the glottic opening. The tube is advanced until the proximal end of the cuff is 1 to 2 cm past the vocal cords, which should place the distal end of the tube midway between the vocal cords and carina. At this point, the laryngoscope blade is removed from the patient’s mouth. The cuff of the endotracheal tube is inflated with air to create a seal against the tracheal mucosa. This seal facilitates positive-pressure ventilation of the lungs and decreases the likelihood of aspiration of pharyngeal or gastric contents. Use of the minimum volume of air in a low-pressure, high-volume cuff that prevents leaks during positive ventilation pressure (20 to 30 cm H2O) minimizes the likelihood of mucosal ischemia resulting from prolonged pressure on the tracheal wall. After confirmation of correct placement (end-tidal CO2, auscultation for bilateral breath sounds, ballottement of cuff in the suprasternal notch), the endotracheal tube is secured in position with tape. The success rate of endotracheal intubation using direct laryngoscopy in patients without a predicted difficult intubation is more frequent than 90%, and in patients with predicted difficult intubation is 84%. (34,35)

Choice of Direct Laryngoscope Blade

The advantages of the curved blade, such as a Macintosh blade, include less trauma to teeth, more room for passage of the endotracheal tube, larger flange size that improves the ability to sweep the tongue, and less bruising of the epiglottis because the tip of the blade does not directly lift this structure. The advantages of the straight blade such as a Miller blade, are better exposure of the glottic opening and a smaller profile, which can be beneficial in patients with a smaller mouth opening.

The tip of the curved blade is advanced into the space between the base of the tongue and the pharyngeal surface of the epiglottis into the vallecula, which elevates the epiglottis and exposes the glottic opening (Fig.13A). The tip of the straight blade is passed beneath the laryngeal surface of the epiglottis (see Fig.13B). Forward and upward movement of the blade exerted along the axis of the laryngoscope handle directly elevates the epiglottis to expose the glottic opening.

Laryngoscope blades are numbered according to their length. A Macintosh 3 and Miller 2 are the standard intubating blades for adult patients. The Macintosh 4 and Miller 3 blades can be used for larger adult patients (Fig.14).

Video Laryngoscopes

Video laryngoscopes can help obtain a view of the larynx by providing indirect visualization of the glottic opening without alignment of the oral, pharyngeal, and tracheal axes and enable endotracheal intubation in patients who have conditions (limited mouth opening, inability to flex the neck) that can make traditional laryngoscopy difficult or impossible. Their ease of use is an advantage over fiberoptic bronchoscopy in these patients. They consist of a handle, light source, and a blade with a video camera at the distal end to enable the glottis to be visualized indirectly on a video monitor. Video laryngoscopes are classified as nonchanneled or channeled.

Nonchanneled blades are Macintosh-style curved blades, Miller-style straight blades, and angulated blades. (18) Types of nonchanneled blades include Glide-Scope, C-MAC, and McGrath.

The Macintosh-style or Miller-style blades can be used for direct laryngoscopy or by viewing the monitor. These blades are inserted using the standard direct laryngoscopy techniques with or without a stylet in the endotracheal tube. The view obtained by looking at the monitor usually offers a slightly improved view compared to looking directly in the patient’s mouth because the camera is more distally located and provides a wider visual field.(36) The advantage of these blades is user familiarity with the blade type and a display that can be used for instructional purposes. (36)

The angulated blades allow for a more anteriorly oriented view that can be obtained with minimal flexion or extension of the patient’s head and neck. (37) The tip of the laryngoscope blade may be placed in the val-lecula or be used to lift the epiglottis directly. These blades usually require a preshaped stylet that matches the curvature of the blade and are usually inserted midline in the mouth, unlike the Macintosh-style blades. An endotracheal tube with the preshaped stylet is advanced using direct visualization in the pharynx until it can be seen on the monitor, after which the tube is advanced into the trachea close to the blade, based on the image on the monitoring screen. Tonsillar and pharyngeal injuries can occur when using video laryngoscopy, especially with rigid stylets when the stylet is advanced through the oropharynx looking at the video screen and not under direct visualization.(38) A limitation of these devices is difficulty directing the endotracheal tube into the glottis despite good glottic visualization. This usually occurs when the laryngoscope is inserted too deeply.(36) Withdrawing the blade slightly, although often giving a poorer laryngoscopic view, can improve the ability to direct the endotracheal tube through the glottic opening.

Channeled devices include the Airtraq and the King Vision Video Laryngoscope. These video laryngoscopes have a guide channel that directs an endotracheal tube toward the glottic opening via blades that are more angulated than traditional Macintosh blades.(36) The endotracheal tube is preloaded into the guide channel and the video laryngoscope is inserted midline in the mouth until the epiglottis is visualized. The blade is advanced into the vallecula or the epiglottis may be directly elevated by the tip of the blade until the cords are visualized. The glottis needs to optimally align on the screen for successful intubation via the channel. Channeled blades tend to have thicker blades than nonchanneled blades requiring a greater interincisor distance.

These techniques can be hindered if upper airway secretions obscure the optics. Video laryngoscopes can also be used on awake patients with topical application of local anesthetic to the airway and are as easy to perform with comparable patient discomfort as fiberoptic intubation.(39) Selected video laryngoscopes are detailed as follows.

GlideScope

The GlideScope has two main blade types: an angulated style blade and a Macintosh-style blade. The reusable blades are made of either titanium or medical-grade plastic (AVL, GVL, and Ranger). The titanium blade offers the advantage of being thinner and hence a lower profile (allowing for insertion with a smaller interincisor distance). The angulated blade is anatomically shaped with a fixed (60-degree) angle and should be used with the GlideRite rigid stylet as this stylet matches the shape of the blade. The blades have a fog-resistant video camera embedded in the undersurface that transmits the digital image to a high-resolution color monitor that can be mounted on a pole. A portable (Ranger) device is also available. There are a variety of different pediatric and adult sizes in reusable and single-use blades (Fig.15).

The GlideScope is associated with improved glottic visualization, especially in patients with potential difficult airways.(34) One study showed the overall success rate with the GlideScope to be 96% in patients with predicted difficult airways and 94% when used as a rescue device for failed direct laryngoscopy.(38) The high success rate of both direct laryngoscopy and video laryngoscopy in patients without a difficult airway emphasizes the advantage of the GlideScope for use in patients with clinical features suggestive of difficult intubation or as a rescue method after failed direct laryngoscopy.(34) Predictors that have been associated with difficult GlideScope use include abnormal neck anatomy, Cormack and Lehane grade 3 or 4 view on direct laryngoscopy, limited mandibular protrusion, and limited cervical spine mobility. (18,38)

C-MAC

The C-MAC (KARL STORZ Endoscopy) has a stainless steel blade with a camera located on the distal end of the blade that displays on a high definition monitor. The interface between the laryngoscope blade and the monitor allows for easy interchange of different blades. The reusable blades come in several sizes and styles including Miller (sizes 0 and 1), Macintosh (sizes 2, 3, and 4), and an angulated D-blade (in pediatric and adult) for difficult airways (Fig.16). The D-blade and the Macintosh size 3 and 4 blades have a lateral guide for an oxygen or suction catheter. The C-MAC is also available in a single-use D-blade and Mac 3 or 4 blade. In difficult airway situations, using the D-Blade improves glottic view and has intubation success rates similar to the GlideScope when compared with direct laryngoscopy. (30,40)

McGrath Scope

The McGrath video laryngoscope is a portable device that consists of an adjustable Macintosh style or angulated (McGrath series 5 or X-blade) single-use polycarbonate blade. The blades are attached to a battery-containing handle mounted with a color display monitor that can rotate and swivel to optimize the angle of visualization. The McGrath video laryngoscope comes in pediatric and adult sizes.

Channeled Scopes: Airtraq and King Vision Scope

The Airtraq is a single-use optical device that creates an image through prisms and mirrors to give a magnified angular view of the glottis. The device has two channels, one for viewing and the other for guiding, supporting, and directing the endotracheal tube toward the glottic opening. (30) Images are displayed on an adjusted screen by a camera. It comes in two models, the Avant with reusable optics and the entirely single-use SP model. The SP model comes in many sizes for infants, pediatric patients, nasotracheal intubations, and double-lumen tubes.

The King Vision Video Laryngoscope is fully portable with a reusable digital display and single-use channeled or nonchanneled blades.

Endotracheal Tube Stylets, Introducers, and Airway Exchange Catheters

A variety of endotracheal tube stylets, introducers, and airway exchange catheters (AECs) may be used in selected patients to facilitate difficult endotracheal intubation, endotracheal tube exchange, and supraglottic airway exchange for an endotracheal tube. In addition, AECs can provide an airway conduit to assist with reintubation. Some of the devices have a hollow lumen and connectors to allow jet ventilation. Ventilation through the lumen should be used only in emergency situations because of the high risk of complications. When using intubating stylets in a patient with a difficult airway, intubation is successful in 78% to 100% of patients. (1) Complications of intubating stylets include bleeding, oropharyngeal trauma, tracheal trauma, and sore throat. Complications of endotracheal tube exchangers include tracheal/bronchial laceration and gastric perforation. (1)

Stylet

Stylets are made from plastic coated, malleable metal that is used to stiffen and provide curvature to an endotracheal tube. After stylet placement through the lumen of an endotracheal tube, the tube can be bent into the desired shape, such as a curve matching a Macintosh blade or a “hockey stick” shape. Although stylets are not necessary with direct laryngoscopy, they can often help facilitate manipulation of the endotracheal tube in the airway. The tip of the stylet should not protrude past the end of the endotracheal tube. When an endotracheal tube is passed through the vocal cords, the stylet should be removed as the tube is advanced into the trachea to avoid trauma.

Gum Elastic Bougie

A gum elastic bougie is a solid 60-cm long, 15-F stylet with a 40-degree curve approximately 3.5 cm from the distal tip. It is used to facilitate intubation in patients with a poor laryngoscopic view. It is passed under the epiglottis and into the airway. A characteristic bumping or clicking is felt in most tracheal placements as the bougie is advanced down the tracheal cartilages, but not felt in all esophageal placements. An endotracheal tube is then advanced over the bougie and into the airway.

Frova Intubating Introducer

The Frova Intubating Introducer is available in a pediatric 35-cm long, 8-F, or an adult 65-cm long, 14-F stylet with a distal angulated tip and an internal channel to accommodate a stiffening rod or allow jet ventilation. The pediatric introducer can be used with endotracheal tubes 3.0 mm and wider and the adult introducer with endotracheal tubes 6.0 mm and wider. The Frova Intubating Introducer is inserted in a similar manner to the gum elastic bougie for patients with poor laryngoscopic views (Fig.17A).

Aintree Intubation Catheter

The AIC (Cook Medical) is 56-cm long, 19-F diameter and has a large, 4.7-mm lumen. It comes with two Rapi-Fit adapters. One is for jet ventilation, and the other for connection to an anesthesia circuit or Ambu bag. It can also be used to exchange supraglottic airways for endotracheal tubes size 7.0 mm or wider. (30)

For exchange of a supraglottic airway, the AIC is threaded onto a fiberoptic bronchoscope. The distal end of the fiberoptic bronchoscope is not covered by the AIC to allow for manipulation. The AIC and fiberoptic bronchoscope are then placed in the lumen of the supraglottic airway and advanced as a unit through the vocal cords into the trachea. The fiberoptic bronchoscope is then removed while the AIC remains in the trachea. The supraglottic airway is removed over the AIC and an endotracheal tube is then placed over the AIC into the trachea. Finally, the AIC is removed (Fig.17B).

Cook Airway Exchange Catheter

Cook AECs are available in pediatric and adult sizes (45- and 83-cm length and 8-, 11-, 14-, or 19-F) as well as an extra-firm soft tip version that is 100-cm long and 11- or 14 -F, for double-lumen tube exchange. They are designed for exchange of endotracheal tubes. They can also be used in the trachea after endotracheal tube removal to help with reintubation if necessary in patients with difficult airways. These catheters are hollow and can allow for jet ventilation or oxygenation through an anesthesia circuit or Ambu bag using Rapi-Fit adapters in emergency situations.(41) For orotracheal intubation, AEC insertion of 20 to 22 cm depth, and for nasotracheal intubation of 27 to 30 cm depth is sufficient for tube exchange and can help avoid complications. If placed deeper, there is risk of bronchial perforation or pneumothorax. To help with placement of an endotracheal tube over an AEC, laryn-goscopy can displace tissues. Using a smaller endotracheal tube may also facilitate the use of AECs.

Flexible Fiberoptic Endotracheal Intubation

Fiberoptic intubation was one of the first techniques introduced for difficult airway management and revolutionized the anesthesia provider’s ability to safely care for these patients. Fiberoptic intubation can be performed through the nose and mouth in awake, sedated, or anesthetized patients. The decision to perform fiberoptic endotracheal intubation in an awake versus an anesthetized patient is dependent on the risk of a difficult airway and the cooperation of a patient. Fiberoptic endotracheal intubation may be advantageous in patients with unstable cervical spines. The technique does not require movement of the patient’s neck and can be performed before induction of general anesthesia, thereby allowing for evaluation of the patient’s neurologic function after endotracheal intubation and surgical positioning.

Patients who have sustained an injury to the upper airway from either blunt or penetrating trauma are at risk for the endotracheal tube creating a false passage by exiting the airway through the disrupted tissue during direct laryngoscopy. By performing a fiberoptic intubation, not only can the injury be assessed, but the endotracheal tube can also be placed beyond the level of the injury, thus minimizing the risk of subcutaneous emphysema.

A disadvantage of fiberoptic endotracheal intubation is that it requires time to set up and prepare the patient’s airway. Another disadvantage is the fiberoptic bronchoscope needs space to pass through. Anything that impinges on upper airway size (edema of the pharynx or tongue, infection, hematoma, infiltrating masses) will make fiberoptic intubation more difficult. Inflating the cuff of the endotracheal tube to hold the pharyngeal walls open may be helpful. Blood and secretions can easily obscure the optics of a fiberoptic bronchoscope making it more challenging. Administering an antisialagogue before initiating fiberoptic intubation and suctioning can minimize view obstruction. A relative contraindication to fiberoptic intubation is the presence of a pharyngeal abscess, which could be disrupted as the endotracheal tube is advanced and result in aspiration of purulent material.

Awake Fiberoptic Endotracheal Intubation

Awake fiberoptic intubation is commonly performed because of examination findings consistent with, or history of, a difficult airway, unstable cervical spine, or airway injury. Performing intubation before induction of anesthesia allows for continuation of spontaneous breathing, preservation of muscle tone, preservation of airway reflexes, and assessment of neurologic function after intu-bation. This is especially important in patients who are at risk for difficult mask ventilation or high aspiration risk. Patient cooperation is critical to this technique.

Awake fiberoptic intubation can be performed through the nose or mouth. In general, the nasal route is easier because the angle of curvature of the endotracheal tube naturally approximates that of the patient’s upper airway. The risk of inducing bleeding is more frequent when the nasal route is used and therefore relatively contraindicated in patients at risk for bleeding, such as those with platelet abnormalities or coagulation disorders.

Patient Preparation

The procedure should be fully explained to the patient. An antisialagogue (glycopyrrolate 0.2-0.4 mg intravenous [IV]) is recommended to inhibit the formation of secretions. The patient should be carefully sedated and monitored throughout the intubation of the trachea. There are many options for sedation, but the more difficult the airway, the less sedation should be used.

Airway Anesthesia

Airway anesthesia is then completed by topical application of local anesthetic, or by specific nerve blocks. Topical application is effective and less invasive than nerve blocks and is usually the preferred method. It can be achieved by spraying (atomizing or nebulizing) or direct application (ointment, gels, or gargling solutions). Several commercial devices are available to assist with topical application of local anesthetic. The larger particle size of a spray tends to cause it to be deposited in the pharynx, with only a small proportion reaching the trachea. Conversely, the small particle size of a nebulized spray is carried more effectively into the trachea, but also into the smaller airways, where the anesthetic is not needed and undergoes more rapid systemic absorption. Lidocaine is the preferred topical local anesthetic because of its broad therapeutic window. Usually 1% and 2% solutions are used for nerve blocks and infiltration whereas 4% solutions are used topically. (42) Benzocaine is less preferred as it can cause methemoglobinemia even in therapeutic doses. Tetracaine has a very narrow therapeutic window, and the maximum allowable dose (1.2 mg/kg) can easily be exceeded. Cetacaine is a mixture of benzocaine and tetracaine and has the disadvantages of each local anesthetic.

Nose and Nasopharynx

The nasal mucosa must be anesthetized and vasoconstriction with 0.05% oxymetazoline hydrochloride (HCL) spray is recommended. In addition to spraying, local anesthetic solutions can be applied directly in the nares on soaked cotton-tipped swabs or pledgets or by nasal airways covered in lidocaine ointment.

Tongue and Oropharynx

Topical anesthesia may be achieved by spraying, direct application, or bilateral blocks of the glossopharyngeal nerve at the base of each anterior tonsillar pillar. Approximately 2 mL of 2% lidocaine injected at a depth of 0.5 cm is sufficient to block the glossopharyngeal nerves on each side. Aspiration with the syringe before injecting the local anesthetic solution is necessary to ensure that the needle is not intravascular or through the tonsillar pillar.

Larynx and Trachea

Anesthesia of the larynx and trachea may be achieved by using the methods described earlier or by superior laryngeal nerve blocks and transtracheal block.

Superior Laryngeal Nerve Block

Injecting local anesthetic solution bilaterally, in the vicinity of the superior laryngeal nerves where they lie between the greater cornu of the hyoid bone and the superior cornu of the thyroid cartilage as they traverse the thyro-hyoid membrane to the submucosa of the piriform sinus, blocks the internal branch of the superior laryngeal nerve. The overlying skin is cleaned with antiseptic solution. The cornu of the hyoid bone or the thyroid cartilage may be used as a landmark. A 22- to 25-G needle is “walked” off the cephalad edge of the thyroid cartilage or the caudal edge of the hyoid bone, and approximately 2 to 3 mL of local anesthetic solution is injected on each side.

Transtracheal Block

For a transtracheal block, the skin is prepared with antiseptic solution and a 20-G IV catheter is advanced through the cricothyroid membrane while simultaneously aspirating with an attached syringe filled with 4 mL of local anesthetic solution. When air is aspirated, the catheter is advanced into the trachea and the needle is withdrawn. The syringe is reattached to the catheter, aspiration of air is reconfirmed, and the local anesthetic solution is rapidly injected. This block is designed to block the sensory distribution of the recurrent laryngeal nerve and prevent coughing with placement of the endotracheal tube in the trachea.

Technique

Nasal fiberoptic intubation of the trachea involves the use of a lubricated endotracheal tube that is at least 1.5 mm larger than the diameter of the fiberoptic bronchoscope. Softening the endotracheal tube in warm water before use makes it less likely to cause mucosal trauma or submucosal tunneling. The endotracheal tube is advanced through the nose into the pharynx by aiming perpendicular to the plane of the patient’s face just above the inferior border of the nasal alar rim. If resistance is met at the back of the nasopharynx, 90 degrees of counterclockwise rotation allows the endotracheal tube to pass less traumatically because the bevel then faces the posterior pharyngeal wall. Secretions should be suctioned before inserting the fiberoptic bronchoscope through the endotracheal tube.

For oral fiberoptic intubation, using a channeled oral airway that fits an endotracheal tube can help keep the fiberoptic scope midline and create space in the oropharynx. Having an assistant gently extend the tongue out of the patient’s mouth can help by elevating the epiglottis. The endotracheal tube can either be advanced in the mouth with the fiberoptic bronchoscope or can be secured at the top of the scope and advanced after the fiberoptic bronchoscope has entered the trachea. Inflation of the endotracheal tube cuff during advancement of the fiberoptic bronchoscope in the pharynx can create an enlarged pharyngeal space and help keep the optics of the fiberoptic bronchoscope from being obscured. The inflated cuff also further aims the tip of the endotracheal tube anteriorly. If the technique of cuff inflation is used to facilitate entry of the bronchoscope into the trachea, the provider should remember to deflate the cuff prior to advancement of the endotracheal tube into the trachea.

The fiberoptic bronchoscope is manipulated to bring the larynx into view, and the bronchoscope is advanced toward the glottic opening. The target should always be kept in the center of the anesthesia provider’s field of vision by flexion/extension and rotation as the fiberoptic bronchoscope is slowly advanced. As the fiberoptic bronchoscope passes through the vocal cords, the tracheal rings will become visible. The scope should be placed just above the carina as the endotracheal tube is threaded over the scope. If resistance is encountered when advancing the endotracheal tube, force should not be exerted as the fiberoptic bronchoscope can become kinked and the endotracheal tube can pass into the esophagus and damage the fiberoptic bronchoscope. Resistance to advancement often means that the endotracheal tube is impacted on an arytenoid. Rotating the endo-tracheal tube as it is gently advanced can relieve this. The appropriate depth of endotracheal tube placement can be verified by observing the distance between the carina and the tip of the endotracheal tube as the fiberoptic bronchoscope is withdrawn. It is essential that the fiberoptic bronchoscope exit the tip of the endotracheal tube and not the Murphy eye. If there is any resistance when removing the fiberoptic bronchoscope, it is probably either through the Murphy eye or kinked in the pharynx. In both instances, the endotracheal tube and the scope must be withdrawn together to avoid damaging the fiberoptic bronchoscope.

Fiberoptic Endotracheal Intubation After Induction of General Anesthesia

Alseep fiberoptic intubation is commonly performed because of examination findings consistent with or history of a difficult airway or unstable cervical spine when mask ventilation is not anticipated to be difficult. It is also an option when patients are not cooperative with awake fiberoptic intubation.

Fiberoptic intubation during general anesthesia can be done either through the nose or the mouth, with the patient breathing spontaneously or under controlled ventilation. To provide supplemental oxygenation during the procedure, a nasal airway can be placed and connected to the anesthesia breathing circuit with a 15-mm connector.

An important difference in performing fiberoptic laryngoscopy in an anesthetized patient is that the soft tissues of the pharynx, in contrast to the awake state, tend to relax and limit space for visualization with the fiberoptic bronchoscope. Using jaw thrust, specialized oral air-ways, inflating the endotracheal tube cuff in the pharynx, or applying traction on the tongue may overcome this problem. It is advisable to have a second person trained in anesthesia delivery assisting when a fiberoptic intubation is performed during general anesthesia because it is difficult to maintain the patient’s airway, be attentive to the monitors, and perform the fiberoptic intubation alone.

When using the nasal approach, it is important to apply a vasoconstrictor to the nasal mucosa to decrease the risk of bleeding, which may obscure the optics of a fiberoptic bronchoscope.

The curvature of the endotracheal tube is not optimal for oral endotracheal intubation, and an appropriately sized channeled oral airway can help. Care must be taken to maintain the intubating airway in a midline position. Alternatively, a supraglottic airway provides an excellent channel for oral fiberoptic intubation.

Endoscopy Mask

The single-use endoscopy mask is designed with a port that will accommodate an endotracheal tube and a fiberoptic bronchoscope through a diaphragm. This device allows for spontaneous or controlled ventilation while fiberoptic nasal or oral intubation is being performed. It is available in newborn, infant, pediatric, and adult sizes.

Blind Nasotracheal Intubation

The use of blind nasotracheal intubation has decreased in frequency over the years with the introduction of other devices for difficult airway management. However, there are still clinical situations in which such a technique can be lifesaving.

A 6.0- to 7.0-mm internal diameter (ID) endotracheal tube is generally chosen for an adult. The endotracheal tube is advanced through the nose and into the pharynx while listening to breath sounds at the distal end of the endotracheal tube. Alternatively, the endotracheal tube can be attached to an anesthesia breathing circuit, and reservoir bag movement and carbon dioxide can be monitored to verify that the endotracheal tube is advancing into the trachea.

Endotracheal Tube Sizes

Endotracheal tube sizes are specified according to their ID, which is marked on each tube. Endotracheal tubes are available in 0.5-mm ID increments. The endotracheal tube also has lengthwise centimeter markings starting at the distal tracheal end to permit accurate determination of the length inserted past the patient’s lips. Endotracheal tubes are most often made of clear, inert polyvinyl chloride plastic that molds to the contour of the airway after softening on exposure to body temperature. Endotracheal tube material should also be radiopaque to ascertain the position of the distal tip relative to the carina and be transparent to permit visualization of secretions or air-flow as evidenced by condensation of water vapor in the lumen of the tube (“breath fogging”) during exhalation.

As noted previously, use the minimum volume of air in a low-pressure high-volume cuff that prevents leaks during positive-pressure ventilation (20 to 30 cm H2O) to minimize risk of mucosal ischemia. Other serious complications attributable to endotracheal cuff pressures include tracheal stenosis, tracheal rupture, tracheoesophageal fistula, tracheocarotid fistula, and tracheoinnominate artery fistula. (43)

Confirmation of Endotracheal Intubation

Confirmation of placement of the endotracheal tube in the trachea is verified by identification of carbon dioxide in the patient’s exhaled tidal volume and clinical assessment. The presence of carbon dioxide in the exhaled gases from the endotracheal tube as detected by capnography (end-tidal PCO2 > 30 mm Hg for three to five consecutive breaths) should be immediate and sustained. Carbon dioxide may initially be present in low concentrations, but will not persist in exhaled gases from a tube accidentally placed in the esophagus.

Symmetric chest rise with manual ventilation, bilateral breath sounds, and absence of breath sounds over the epigastrium is confirmed after endotracheal intubation. Palpation or balloting of the endotracheal tube cuff in the suprasternal notch can help determine endotracheal versus endobronchial intubation. Progressive decreases in oxygen saturation on a pulse oximeter may alert the anesthesia provider to a previously unrecognized esophageal intubation.

In adults, taping the endotracheal tube at the patient’s lips corresponding to the 21- to 23-cm markings on the endotracheal tube usually places the distal end of the endotracheal tube in the midtrachea. Of note, flexion of the patient’s head may advance and convert a tracheal placement into an endobronchial intubation, especially in children. Conversely, extension of the head can withdraw the tube and result in inadvertent extubation.

Rapid Sequence Induction of Anesthesia With Cricoid Pressure

Cricoid pressure (Sellick maneuver) may prevent spillage of gastric contents into the pharynx during the period from induction of anesthesia (unconsciousness) to successful placement of a cuffed endotracheal tube. It can be applied by an assistant exerting downward external pressure with the thumb and index finger on the cricoid cartilage to displace the cartilaginous cricothyroid ring posteriorly and thus compress the underlying upper esophagus against the cervical vertebrae (Fig.18). The magnitude of downward external pressure (30 newtons is recommended) that needs to be exerted on the cricoid cartilage to reliably occlude the esophagus is difficult to judge. The use of cricoid pressure has been questioned for several reasons including the following: (1) there is lack of validation in models other than cadavers, (2) there have been reports of aspiration despite its use, (3) it can cause relaxation of the lower esophageal sphincter, which can favor regurgitation, (4) it may cause complications such as increasing the difficulty of mask ventilation or worsening laryngoscopic view or nausea, vomiting, and esophageal rupture, and (5) magnetic resonance imaging has shown that the esophagus may be lateral and not directly posterior to the cricoid cartilage in patients with or without application of cricoid pressure resulting in inadequate esophageal compression. (44,45) Other magnetic resonance imaging studies have suggested that although the esophagus is laterally displaced in some patients, the hypopharynx is the structure that is being compressed by cricoid pressure, and the cricoid and hypopharynx move together as a unit. Even if lateral movement occurs, there is compression of this structure. (46) The use of cricoid pressure remains controversial. It should probably be considered in selected patients with increased risk for regurgitation of gastric contents during induction of anesthesia, but can be released if it impedes oxygenation, ventilation, or view of glottic structures.

In situations when ventilation and intubation are unsuccessful despite use of a supraglottic airway, emergency invasive access should be used.  (1) Invasive emergency access consists of percutaneous or surgical airway, jet ventilation, and retrograde intubation. Predictors of difficult access through the cricothyroid membrane include increased neck circumference, overlying neck malformation, and a fixed cervical spine flexion deformity. (18,47)

Cricothyrotomy

A cricothyrotomy can be a lifesaving procedure in a “can-not intubate, cannot ventilate” situation or can be used as a first-line technique to secure an airway when using a less invasive technique is not possible owing to factors such as facial trauma, upper airway bleeding, or upper airway obstruction. A cricothyrotomy is best performed with the patient in the sniffing position to optimize the ability to identify the cricothyroid membrane. A percutaneous cricothyrotomy uses the Seldinger technique. A needle is advanced at a 90-degree angle through the cricothyroid membrane while aspirating with an attached syringe. A change in resistance is felt as a pop when the needle enters the trachea and air is aspirated. The needle should be directed caudally at a 30- to 45-degree angle. A guidewire is then advanced through the needle, followed by removal of the needle, a small incision adjacent to the wire, and placement of a combined dilator and airway of adequate caliber (>4 mm). Finally, the wire and dilator are removed leaving the airway in place. (47)

The surgical technique involves a vertical or horizontal skin incision, followed by a horizontal incision through the cricothyroid membrane through which a standard endotracheal tube or tracheostomy tube is placed. A tracheal hook, dilator, AEC, or bougie can assist in placement of the airway. (48,49) A surgical cricothyrotomy can also be valuable as a rescue technique if a percutaneous cricothyrotomy is unsuccessful. There are commercial percutaneous and surgical cricothyrotomy kits available that require minimal assembly for use in emergency circumstances.

Both techniques can provide a cuffed endotracheal tube to bypass upper airway obstruction, provide ventilation, and protect against aspiration. There is no consensus on which technique is superior. (48,49) Success of either technique relies on knowledge, practice, proficiency, and performing the cricothyrotomy early when in a “cannot intubate, cannot ventilate” situation. Some relative contraindications to either technique are laryngeal or tracheal disruption and coagulopathy. Complications include bleeding, laryngeal, tracheal or esophageal injury, infection, and subglottic stenosis. (18,49)

Transtracheal Jet Ventilation

Transtracheal jet ventilation is achieved by placement of an over-the-needle catheter in the trachea through the cricothyroid membrane. The cricothyroid membrane should be identified and a catheter over a needle connected to a syringe should puncture the membrane at a 90-degree angle until air is aspirated. The catheter should be advanced off the needle into the trachea at a 30- to 45-degree angle caudally. After reconfirming correct placement by aspiration of air, the catheter should be connected to a high-pressure oxygen source. Commercially available products contain kink-resistant catheters and specialized tubing for high-pressure (50 psi) ventilation. The risk for transtracheal jet ventilation includes pneumothorax, pneumomediastinum, bleeding, infection, and subcutaneous emphysema. (49) Contraindications to transtracheal jet ventilation are upper airway obstruction or any disruption of the airway. (50)

Retrograde Endotracheal Intubation

Retrograde endotracheal intubation can be performed without identification of the glottic inlet. It has been used in cases of anticipated and unanticipated difficult airway management, particularly when there is bleeding, airway trauma, decreased mouth opening, or limited neck movement.

The cricothyroid membrane is punctured with a needle in the method previously described. Once in the trachea, the syringe is detached and a guide (usually a wire or catheter) is threaded through the needle in a cephalad direction. It is then retrieved from the mouth or nose. An endotracheal tube, with or without a fiberoptic bronchoscope, is threaded over the wire until it stops on impact with the anterior wall of the trachea. Tension on the guide can be relaxed to allow the endotracheal tube to pass further into the trachea before removing the wire. Commercially available kits have improved this technique by adding a guiding catheter that fits over the wire and inside the endotracheal tube. Contraindications include disease of the anterior aspect of the neck (tumors, infection, stenosis) or coagulopathy. (51)

Endotracheal Extubation

Endotracheal extubation after general anesthesia requires skill and judgment. The patient must be either deeply anesthetized or fully awake at the time of endotracheal extubation. The risk and benefits of either technique should be taken into account when planning for extubation. As with intubation, 100% O2 should be administered prior to extubation. Any residual neuromuscular blockade should be reversed. The oropharynx is suctioned and a bite block should be placed to prevent occlusion of the endotracheal tube. Once the patient has met routine endotracheal extubation criteria, such as spontaneous respirations with adequate minute ventilation, satisfactory oxygenation and acid base status, and hemodynamic stability, the endotracheal tube can be removed. Patients who are obese or have a history of obstructive sleep apnea may benefit from positioning with the head up for extubation.(52) For deep extubation, adequate anesthesia should be confirmed and for awake patients, they should be able to follow commands. Endotracheal extubation during a light level of anesthesia (disconjugate gaze, breath-holding or coughing, and not responsive to commands) increases the risk of laryngospasm. Laryngospasm is unlikely if the depth of anesthesia is sufficient so laryngeal reflexes are suppressed or the patient is allowed to awaken before endotracheal extubation so laryngeal reflexes are intact. A patient reaching for the endotracheal tube might indicate a localizing response to noxious stimulation despite not being awake enough from anesthesia to follow commands. The endotracheal tube cuff is then deflated and the endotracheal tube rapidly removed from the patient’s trachea and upper airway while a positive-pressure breath is delivered to help expel any secretions. After endotracheal extubation, 100% O2 is delivered by face mask and airway patency and adequate ventilation and oxygenation are confirmed.

Tracheal extubation before the return of protective airway reflexes (deep endotracheal extubation) is generally associated with less coughing and attenuated hemodynamic effects on emergence. This may be preferred in patients at risk from adverse effects of increased intracranial or intraocular pressure, bleeding into the surgical wound, or wound dehiscence. Previous difficult face mask ventilation or endotracheal intubation, high risk of aspiration, restricted access to the airway, obstructive sleep apnea or obesity, and a surgical procedure that may have resulted in airway edema, bleeding or increased irritability are relative contraindications to deep endotracheal extubation. Deep extubation may also predispose to airway obstruction owing to the remaining anesthetic drug present.

If a patient is at risk for failure of extubation and may be a difficult reintubation, a plan for reintubation must be made (Fig.19). High-risk patients include those with airway edema, inadequate ventilation, and history of a difficult intubation.(18) Checking for a cuff leak can help determine if significant airway edema is present. This can be done easily in a spontaneously breathing patient by removing him or her from the ventilation circuit, deflating the endotracheal tube cuff, and obstructing the end of the endotracheal tube. Breath sounds are evidence of air movement around the endotracheal tube. Extubation over an AEC or insertion of supraglottic airway prior to extubation provides a conduit to reintubation and allows for oxygenation and/or ventilation if necessary.(1,53) Extubation of the trachea is always elective, and postponing extubation may be appropriate in some cases when the patient has increased risk for requiring reintubation.

Complications of endotracheal intubation are rare and should not influence the decision to place an endotracheal tube. Complications of endotracheal intubation may be categorized as those occurring (1) during direct laryngoscopy and endotracheal intubation, (2) while the endotracheal tube is in place, and (3) after endotracheal extubation (Box 2)

Complications During Laryngoscopy and Endotracheal Intubation

Direct upper airway trauma is more likely to occur with difficult endotracheal intubation because often there is increased physical force applied to the patient’s airway than normal, as well as the need for multiple attempts at intubation. One of the most common consequences of using increased physical force with a laryngoscope is dental damage (occurs in 1 in 4500 patients). (54) Other patients at risk for dental injury include those with preexisting poor dentition or fixed dental work. Use of a plastic shield placed over the upper teeth may help in selected patients but also decreases the interincisor distance, which may make laryngoscopy more difficult. Other risks include oral or pharyngeal injury, lip lacerations and bruises, and laryngeal, arytenoid, esophageal, or tracheal damage.

Laryngoscopy and intubation are associated with systemic hypertension, tachycardia, and increased intracranial pressure. These responses are generally short lived and of little consequence in most patients. In patients with preexisting hypertension, ischemic heart disease, or certain neurologic conditions, these responses can cause harm. Aspiration poses another potential risk, especially in patients who are not fasted, have symptomatic gastroesophageal reflux, have delayed gastric emptying, or are morbidly obese. Aspiration is the most common cause of death among major anesthesia airway complications. (8) If inadequate oxygenation or ventilation is prolonged after induction of anesthesia, patients may develop cardiac dysrhythmias and in rare cases cardiac arrest and brain damage.

Complications While the Endotracheal Tube Is in Place

These complications include obstruction or accidental esophageal or endobronchial endotracheal tube placement. Obstruction of the endotracheal tube may occur as a result of secretions or kinking. The chance of endobronchial intubation or accidental extubation can be minimized by calculating the proper endotracheal tube length for the patient and then noting the centimeter marking on the tube at the point of fixation at the patient’s lips. Care should be taken if the neck position changes to confirm the endotracheal tube is correctly positioned.

Complications After Endotracheal Extubation

One third of adverse airway events occur during emer-gence or recovery from anesthesia. (8) Most of them are due to airway obstruction from factors such as laryngeal edema, laryngospasm, or bronchospasm. A patient who is lightly anesthetized at the time of endotracheal extubation is most at risk for laryngospasm. If laryngospasm occurs, oxygen delivered with positive pressure through a face mask and jaw thrust may be sufficient treatment. Administration of succinylcholine or an anesthetic drug, such as propofol, is indicated if laryngospasm persists. 

Sore throat is present in about 40% of patients after laryngoscopy and endotracheal intubation and in 20% to 42% of patients after LMA placement.(55) Sore throat after laryngoscopy and intubation is more frequent in females and there is evidence of previous airway trauma in all genders. Use of larger endotracheal tubes and overinflating endotracheal tube cuffs may also increase the likelihood of sore throat. Sore throat is usually self-limiting and resolves in 24 to 72 hours.

The major complication of prolonged endotracheal intubation (>48 hours) is damage to the tracheal mucosa, which may progress to destruction of cartilaginous rings and subsequent fibrous scar formation and tracheal stenosis. Using high-volume, low-pressure cuffs and keeping cuff pressures less than 25 cm H2O can help prevent this complication.

Airway Management Differences Between Infants and Adults

Understanding the differences between the infant and adult airway is critical to proper airway management in pediatric anesthesia (Box 3). The anatomic and physiologic differences between the infant airway and the adult airway decrease as the child grows; they resolve by about 10 to 12 years of age.

The epiglottis in an infant’s airway is often described as relatively larger, stiffer, and more omega-shaped than an adult epiglottis. More importantly, an infant’s epiglottis is typically angled in a more posterior position, thereby blocking the view of the vocal cords during direct laryngoscopy. In infants and small children, it is often necessary to lift the epiglottis with the tip of the blade of the laryngoscope to visualize the vocal cords and successfully intubate the trachea.The larynx in infants is located higher in the neck than in adults. In infants, the larynx is typically at the level of C3-C4 and in adults, the larynx is usually at the level of C4-C5. The higher larynx in infants causes the tongue to shift more superiorly, closer to the palate. As a result, the tongue more easily apposes the palate, which can cause airway obstruction in situations such as inhalation induction of anesthesia. An infant’s tongue is also larger in proportion to the size of the mouth than in adults. The relatively large size of the tongue makes direct laryngoscopy more difficult and can contribute to obstruction of the upper airway during sedation, inhalation induction of anesthesia, and emergence from anesthesia. Anterior pressure on the angle of the mandible, commonly referred to as jaw thrust, will often shift the tongue to a more anterior position and resolve an upper airway obstruction. An oral or nasal airway can also be beneficial in these situations.

An infant’s airway is often described as funnel-shaped, with a relatively large thyroid cartilage above and a relatively narrow cricoid cartilage below. The cricoid cartilage is the narrowest portion of an infant’s airway; the vocal cords are the narrowest portion of an adult’s airway. The cricoid cartilage is circular, allowing cuffed or uncuffed endotracheal tubes to successfully seal and protect the airway from aspiration.

An infant’s head and occiput are relatively larger than an adult’s. The proper position for direct laryngoscopy and endotracheal intubation in an adult is often described as the sniffing position with the head elevated and the neck flexed at C6-C7 and extended at C1-C2. An infant, on the other hand, requires a shoulder roll or neck roll to establish an optimal position for face mask ventilation and direct laryngoscopy. An infant’s nares are relatively smaller than an adult’s and can offer significant resistance to airflow and increase the work of breathing, especially when secretions, edema, or bleeding narrow them.

Oxygen consumption per kilogram is much higher in infants than in adults. This results in a much shorter allowable time for intubation before the infant desaturates, even after adequate preoxygenation (see Fig.8). This can be a significant issue, especially in difficult intubations.

Managing the Normal Airway in Infants and Children

A complete history and a focused physical examination are the first steps in managing the pediatric airway.

History

The history should include whether there were any problems with previous anesthetics; prior anesthetic records should be reviewed if they are available. A history of snoring should prompt additional questioning about whether the infant or child has obstructive sleep apnea. If present, respiratory obstruction may develop during the induction and emergence phases of anesthesia, as well as in the postoperative period, especially if opioids are used for pain management. There are numerous syndromes associated with difficult airway management, most of which involve mandibular hypoplasia or cervical spine abnormalities that limit flexion and extension (see Table 2).

Physical Examination

It is often difficult to perform a complete physical examination on infants and children. Asking a child to look up at the sky and then down at the floor is one way of assessing neck extension and flexion, respectively. If there are any masses, tumors, or abscesses in the neck or upper airway that compromise neck flexion, extension, or breathing function, further evaluation is important and should include computed tomography to evaluate the location and degree of any airway compromise. Children will often voluntarily open their mouths to enable determination of a Mallampati classification. If an infant or child is uncooperative, external examination of the airway often reveals enough information to determine whether it is a normal or potentially difficult airway. Examining the profile of an infant or child can indicate whether the thyromental distance is short and whether the patient has micrognathia or a hypoplastic mandible.

The parent(s) and the child should be directly asked whether there are any loose teeth. If loose teeth are identified, care should be taken to avoid traumatizing these teeth during airway management. Very loose teeth should be removed before proceeding with airway management to prevent the possibility of dislodgement and aspiration.

Preanesthetic Medication and Parental Pres-ence During Induction of Anesthesia

Parental presence during induction of anesthesia is increasingly becoming the standard approach for pedi-atric patients. Parental presence can minimize the need for preanesthetic medication in infants and children. Anxious parents can transfer their anxiety to their children. Therefore, it is important to spend adequate time preoperatively addressing any questions or concerns of both the child and the parents. Child-life services should be available preoperatively to use age-appropriate play therapy, preoperative instruction, and coping skills for both the child and the parents. The goal is to decrease anxiety and prepare them for the experience of the induction of anesthesia in the operating room. It is important to designate a member of the operating team to escort the parents from the operating room to the waiting area after the induction of anesthesia is completed and to address any worries parents may have after witnessing the procedure.

Preanesthetic medication can facilitate the induction of anesthesia in very anxious children. Preanesthetic medication is often not necessary in infants younger than 6 months because stranger anxiety does not usually develop until 6 to 9 months of age. If the child has an IV catheter in place, midazolam can be administered in small doses and titrated to effect. It is important to recog-nize that a higher per kilogram dose of IV midazolam is required in young children than in adults. Although the goal for premedication with midazolam in adults is often anxiolysis, the goal for premedication in young children is often sedation, thus, the higher per kilogram dosing.

If the child does not have an IV catheter in place, midazolam syrup can be given orally in a dose of about 0.5 mg/kg up to a maximum dose of about 20 mg. If the child is uncooperative with taking oral midazolam and preanesthetic medication is essential, midazolam can also be given intranasally, intramuscularly, or rectally. In rare cases in which older children are uncooperative, agitated, or violent, it may be necessary to administer intramuscular ketamine in a dose of about 3 mg/kg to facilitate IV placement and the induction of anesthesia.

Induction of Anesthesia

If the infant or child has an IV catheter, induction of anesthesia with propofol is usually safer and quicker than an inhaled induction of anesthesia. After the infant or child loses consciousness and the ability to ventilate with a face mask is verified, either a supraglottic airway device can be inserted or a neuromuscular blocking drug can be given to facilitate direct laryngoscopy and endotracheal intubation. Although it is possible to perform laryngoscopy on infants and children without a neuromuscular blocking drug, using a neuromuscular blocking drug, such as rocuronium, facilitates laryngoscopy and intubation, decreases the incidence of laryngospasm, and decreases the amount of pro-pofol required for the induction of anesthesia. For routine situations, a dose of 0.3 to 0.6 mg/kg of rocuronium is recommended.

When the infant or child does not have an IV catheter in place, inhaled induction of anesthesia can be performed. Beginning the induction of anesthesia with the odorless mixture of nitrous oxide and oxygen through a face mask, then slowly increasing the concentration of sevoflurane is the best approach in a cooperative child. If the child is uncooperative, it is better to induce with 8% sevoflurane. When the infant or child becomes unconscious, the nitrous oxide should be turned off to administer 100% oxygen to adequately preoxygenate prior to laryngoscopy. The increasing level of anesthesia will decrease skeletal muscle tone and can cause upper airway obstruction in infants and children. If upper airway obstruction occurs, it can usually be relieved by a jaw thrust, or by inserting an oral or nasal airway. An IV catheter should then be placed. Once the ability to ventilate the patient has been confirmed, either a supraglottic airway device can be inserted, or a neuromuscular blocking drug can be given to facilitate laryngoscopy and endotracheal intubation.

Direct Laryngoscopy and Endotracheal Intubation

When performing direct laryngoscopy and endotracheal intubation in infants and children, it is important to appropriately position the infant or child with a roll under the neck or shoulders. The oropharynx should be visualized as divided into three compartments: (1) the tongue swept to the left by the laryngoscope blade, (2) the laryngoscope blade in the middle of the mouth, and (3) the endotracheal tube entering from the right side of the mouth. Gentle, external posterior pressure applied with the fingers of the anesthesia provider’s right hand at the level of the thyroid or cricoid cartilage is sometimes necessary to bring the vocal cords into view.

Once the trachea is intubated, correct positioning of the endotracheal tube should be confirmed by endtidal CO2, by watching the chest rise and fall, and by auscultation of both right and left lungs. Because the trachea in infants and children is short, it is easy to accidentally intubate a main bronchus. The correct depth of a cuffed endotracheal tube can be estimated by palpating the endotracheal tube cuff in the suprasternal notch. The correct tracheal depth of an uncuffed endotracheal tube can be estimated by placing the double line at the distal end of the endotracheal tube at the vocal cords while performing direct laryngoscopy. In infants and children, it is important to reconfirm that the endotracheal tube is correctly positioned by listening for equal bilateral breath sounds after securing the endotracheal tube, and whenever there is a change in the patient’s position.

Airway Equipment

Nasal and Oral Airways

Nasal and oral airways can sometimes be useful in pediatric patients to relieve airway obstruction, especially during face mask ventilation at the beginning or end of anesthesia. The nasal airway should be carefully placed through one of the nares after lubricating its exterior. The nasal airway must be long enough to pass through the nasopharynx, but short enough that it still remains above the glottis.

Oral airways relieve airway obstruction by displacing the tongue anteriorly. Too large an oral airway will either obstruct the glottis or may cause coughing, gagging, or laryngospasm in a patient who is not deeply anesthetized. Too small an oral airway will push the tongue posteriorly and make the airway obstruction worse. Oral airways should be placed with care to prevent trauma to the teeth and oropharynx.

Supraglottic Airway Devices

Supraglottic airway devices are placed in the patient’s oropharynx to facilitate oxygenation and ventilation; they can also deliver inhalational anesthetics. They can be used for both routine airway management and dif-ficult airway situations. Although supraglottic airway devices are ideally suited for situations in which the patient is breathing spontaneously, they can also be used to deliver positive-pressure ventilation. Care must be taken when using positive-pressure ventilation with a supraglottic airway device to minimize peak inspiratory pressure. Patients who have lung disease or whose peak inspiratory pressures are higher than normal are poor candidates for a supraglottic airway device. In these patients, air may leak into the esophagus resulting in distention of the stomach and increase the risk for emesis and aspiration. Supraglottic airway devices do not protect the airway from aspiration. They should not be routinely used in patients with full stomachs or those at increased risk for aspiration. Many supraglottic airway devices are available in both single-use and reusable versions.

Laryngeal Mask Airways

LMAs are supraglottic airway devices that have proved to be very useful in managing the pediatric airway. The LMA Classic and the LMA Unique, which is the single-use version of the LMA Classic, are both available in seven sizes appropriate for a range of pediatric patients. The LMA ProSeal and the LMA Supreme, which is the single-use version of the LMA ProSeal, are also available in the same seven sizes. The LMA ProSeal and Supreme have an additional lumen that is designed to vent the esophagus. The LMA Flexible is essentially the LMA Classic with a wire-reinforced airway tube that resists kinking. It can minimize interference with surgical procedures involving the head and neck. The LMA Flexible is not available in sizes 1 and 1½. It is the most difficult LMA to insert; a stylet may be required to facilitate insertion.

The appropriate size LMA is most easily determined by using the weight of the infant or child (Table 5). An LMA that is too large will be more difficult to place. An LMA that is too small will not form a good seal, making positive-pressure ventilation more challenging.

After the LMA has been inserted and its cuff has been inflated, correct positioning should be confirmed by auscultation of breath sounds and by end-tidal CO2. Ideally, the cuff of the LMA should be inflated with just enough air to allow positive-pressure ventilation. Overinflation of the LMA cuff has been associated with mucosal damage and postoperative sore throat and may not decrease the leak pressure. (56,57) It is important to realize that the cuff pressure can be much higher than the leak pressure. Ideally, the pressure in the cuff of the LMA should be measured with a manometer (Fig. 20) and should be less than 30 to 40 cm H2O.

Air-Q Masked Laryngeal Airways

Air-Q intubating laryngeal airways (ILAs) are another type of supraglottic airway device used with infants and children. They are available in single-use and reusable versions. Their major advantage over LMAs is a design that facilitates endotracheal intubation with standard oral endotracheal tubes. The Air-Q’s airway tube has a larger diameter than the LMA, allowing for intubation with a larger endotracheal tube than the correspondingly sized LMA. The Air-Q ILA can be used with a specially designed ILA removal stylet that stabilizes the endotracheal tube and allows controlled removal of the ILA, without dislodging the endotracheal tube from the trachea. The Air-Q ILA is available in seven sizes appropriate for a range of pediatric patients. As with the LMA, determining the appropriate size is most easily estimated by using the weight of the infant or child (Table 6). The 0.5 size Air-Q ILA is currently available only in the reusable version.

Endotracheal Tubes

The appropriately sized endotracheal tube for infants and children can be estimated by using the following formula for uncuffed endotracheal tubes only: (Age + 16)/4 = endotracheal tube (ID) size

To adapt this formula to cuffed endotracheal tubes it is necessary to subtract half a size from the calculated size, because the cuff is located on the outside of the endotracheal tube. Endotracheal tubes a half size larger and a half size smaller than calculated should always be available. Endotracheal tube size can also be based on patient age and body weight. An appropriately sized suction catheter should also always be available to suction secretions, blood, or fluid from the endotracheal tube (Table 7).

Cuffed Versus Uncuffed Endotracheal Tubes

Historically, uncuffed endotracheal tubes were used in infants and smaller children, but more recently cuffed endotracheal tubes have been used increasingly in pediatric anesthesia. With cuffed endotracheal tubes, the cuff is on the outside of the endotracheal tube and adds to the external diameter. Using a cuffed tube often necessitates using a 0.5 mm ID smaller endotracheal tube than using an uncuffed tube. The smaller ID cuffed tube has more resistance to airflow and creates more work of breathing. The increased work of breathing in the slightly narrower cuffed tube is insignificant now that ventilators are available to decrease the work of breathing. Using cuffed endotracheal tubes minimizes the need for repeated laryngoscopy, allows for lower fresh gas flows, decreases the amount of inhalational anesthetic used, and decreases the concentrations of anesthetic gases detectable in operating rooms. (58) Using cuffed endotracheal tubes does not increase the incidence of postextubation croup when compared to the use of uncuffed endotracheal tubes.(59,60)

When cuffed endotracheal tubes are used in infants and children, the cuff pressure should be measured and adjusted to maintain a cuff pressure of approximately 20 to 25 cm H2O. A leak pressure may be used to approximate a cuff pressure, but ideally the cuff pressure should be measured directly with a manometer (see Fig. 20) as this will most closely correlate with the pressure of the cuff on the tracheal mucosa. If the cuff pressure is too low, it will be difficult to ventilate the patient with positive pressure. If the cuff pressure is too high, this can cause tracheal mucosal injury, postoperative sore throat, and postextubation croup. (61) In rare cases, often involving prolonged intubation, cuff pressures that are too high can result in tracheal stenosis. If nitrous oxide is used during the case, or in cases in which there is the potential for significant airway edema, the cuff pressure should be monitored periodically during the case. The cuff pressure should be measured and recorded in the anesthesia record.

When uncuffed endotracheal tubes are used in infants and children, the leak pressure should be checked. The correct size uncuffed endotracheal tube is one that results in a leak pressure of approximately 20 to 25 cm H2O. If the uncuffed tube is too large, the leak pressure will be too high. In this situation, the endotracheal tube should be replaced with a smaller one to prevent tracheal mucosal injury, postextubation croup, and the possibility of subsequent tracheal stenosis. If the uncuffed tube is too small, the leak pressure will be too low. In this situation it will be difficult to ventilate the patient with positive pressure and the endotracheal tube should be replaced with a larger one. The leak pressure should be measured and documented in the anesthesia record.

Microcuff Endotracheal Tubes

Microcuff pediatric endotracheal tubes offer several distinct advantages over conventional pediatric cuffed endotracheal tubes. Microcuff endotracheal tubes have a cuff made from a microthin polyurethane membrane that is 10 μm thick. The cuff is also cylindrical, rather than round or oval. These tubes seal the airway at lower cuff pressures than conventional endotracheal tubes, reducing the potential for tracheal mucosal edema and postextubation croup; however, using Microcuff endotracheal tubes does not eliminate the incidence of postextubation croup. The appropriately sized endotracheal tube must be used and the inflation pressure should be measured.(62) The cuff on the Microcuff endotracheal tube is also shorter and placed closer to the tip of the endotracheal tube, which increases the likelihood that the tube is correctly placed. In addition, the Microcuff endotracheal tube has an intubation depth mark indicating the correct depth for insertion, increasing the probability of correct placement. Microcuff endotracheal tubes are available in sizes ranging from 3.0 to 7.0 mm, in 0.5-mm increments, in both straight and curved versions.

Stylet

Using a stylet stiffens the endotracheal tube and makes it easier to manipulate during direct laryngoscopy and endotracheal intubation. The appropriately sized stylet should always be immediately available (see Table 7).

Laryngoscopes

In general, a straight-blade laryngoscope is easier to use in infants and small children than a curved blade. The smaller profile of the straight blade than the curved blade is easier to use in smaller mouths. The smaller tip of the straight blade more effectively lifts the epiglottis than the curved blade. However, curved blades have a larger flange that retracts the tongue to the left more effectively and may be useful in patients with larger than normal tongues (e.g., Beckwith-Wiedemann syndrome, trisomy 21).

In infants younger than 1 year, a Miller 1 straight laryngoscope blade is most useful. In children between 1 and 3 years of age, a 1½ straight laryngoscope blade, such as a Wis-Hipple, is recommended. A longer straight laryngoscope blade such as a Miller 2 is appropriate for most children between 3 and 10 years of age. The tracheas of children older than 11 years are often more easily intubated with a curved laryngoscope blade, such as a Macintosh 3. Both straight and curved laryngoscope blades of various sizes should always be immediately available.

Video Laryngoscopes

Video laryngoscopes are very useful tools for managing both the unexpected and expected difficult pediatric intubation. Video laryngoscopes have a camera and a light source near the tip of the blade and a separate video display. Although direct laryngoscopy requires a direct line of sight to the glottic opening and vocal cords, video laryngoscopy allows the anesthesia provider to view the glottic opening indirectly, without the need for aligning the oral, pharyngeal, and laryngeal axes (see Fig.7). Thus, the major advantage of video laryngoscopy over direct laryngoscopy is the ability to see “around the corner” to view the glottic opening and vocal cords, even in patients with limited neck extension, hypoplastic mandibles, or “anterior”  airways.

Video laryngoscopy is easier to learn than fiberoptic bronchoscopy because it mimics the skills of direct laryngoscopy. Video laryngoscopy is a better tool than direct laryngoscopy for teaching both the routine and difficult airway because both the student and teacher can view the monitor at the same time.

Video laryngoscopy requires adequate mouth opening to allow space both for placing the video laryngoscope for an optimal view and for manipulating the endotracheal tube so that it is able to pass through the vocal cords. Video laryngoscopy has been shown in studies to improve the ability to see the glottic opening and vocal cords in pediatric patients with both normal and difficult airways. However, these studies have also demonstrated the need for increased time to intubate, as well as higher failed intubation rates compared to direct laryngoscopy. (34,63,64)

GlideScope Video Laryngoscopes

The GlideScope video laryngoscope consists of different types of both single-use and reusable video laryngoscopes. Digital cameras are mounted at the tips of the blades or the video batons. The video image is viewed on a standalone, high-resolution monitor. The newest GlideScopes are the titanium models that are available in both single-use and reusable models (see Fig. 15). The T3 is a curved bladed style suitable for children weighing more than 10 kg and the T4 is suitable for children more than 40 kg. Titanium models are not currently available in sizes suitable for neonates, infants, and children less than 10 kg. The GlideScope AVL models consist of a video baton inserted into a single-use plastic blade. The GVL 0 is designed for infants weighing less than 1.5 kg, the GVL 1 for infants from 1.5 to 3.0 kg, the GVL 2 for infants from 1.8 to 10 kg, and the GVL 2.5 for children from 10 to 28 kg  (Table 8).

C-MAC Video Laryngoscopes

The C-MAC video laryngoscope consists of a camera with a wide-angle lens mounted at the tip of a reusable stainless steel blade, with a video display on a standalone, high-resolution monitor. The blades are available in curved Macintosh shape in sizes 2, 3, and 4, as well as straight Miller shape in sizes 0 and 1 for neonates and infants, respectively. There is also a D blade that is more curved than the Macintosh blade and is designed for difficult airways (see Fig.6). The D blade is available in two sizes, pediatric and adult, but is too large for infants and small children (see Table 8).

McGrath MAC Video Laryngoscopes

The McGrath MAC video laryngoscope consists of a reusable video laryngoscope that is inserted into a single-use plastic curved blade, with a video display mounted on the handle of the laryngoscope. It is available in sizes 2, 3, and 4 corresponding to regular Macintosh blade sizes 2, 3, and 4, respectively. The McGrath MAC video laryngoscopes are most suitable for children 4 years of age or older (see Table 8).

Fiberoptic Bronchoscopes

A flexible fiberoptic bronchoscope is another tool for managing a difficult pediatric airway. It is particularly valuable when the patient’s mouth opening or neck mobility is limited. Disadvantages of a fiberoptic bronchoscope include a limited field of vision and interference from bleeding and secretions. The smallest fiberoptic bronchoscopes are 2.2 mm in diameter and can be used for endotracheal tubes as small as 3.0 mm ID. These small bronchoscopes, however, do not have a suction channel; they also have optics inferior to larger scopes. In general, the fiberoptic bronchoscope should be at least 1 mm smaller in outside diameter than the ID of the endotracheal tube.

Infants and children are unlikely to be able to cooper-ate with an awake fiberoptic intubation. Therefore, it is easier to perform an asleep fiberoptic intubation. Some anesthesia providers prefer to maintain spontaneous ventilation during fiberoptic laryngoscopy and endotracheal intubation, especially if there is concern about the ability to ventilate the patient’s lungs with a face mask. Frequently, it is easier to administer neuromuscular blocking drugs to a pediatric patient to provide better viewing conditions, including less movement, less fogging of the bronchoscope, and less chance of laryngospasm. Using an elbow with a port that permits insertion of the fiberoptic bronchoscope allows for either continued spontaneous ventilation or assisted positive-pressure ventilation through the face mask.

For nasal fiberoptic laryngoscopy and endotracheal intubation, a vasoconstrictor, such as oxymetazoline hydrochloride 0.05% nasal spray, should be administered to the nasal mucosa to prevent or minimize nasal bleeding, which makes viewing the glottis and vocal cords more challenging. Phenylephrine should not be administered for vasoconstriction to the nasal mucosa of infants and small children because of the risk of phenylephrine toxicity.

For oral fiberoptic laryngoscopy and endotracheal intubation, a supraglottic airway device can provide an excellent channel directly to the vocal cords by shielding the bronchoscope from secretions and blood. It is recommended to select the largest endotracheal tube that will easily fit through the s upraglottic airway device and the largest bronchoscope that will fit through the endotra-cheal tube. If a supraglottic airway device is used as a conduit for oral fiberoptic laryngoscopy and endotracheal intubation, it is simplest to leave the supraglottic airway device in place until the end of the procedure, while partially deflating the cuff to prevent unnecessary pressure on the mucosa of the oropharynx.

Managing the Difficult Airway in Infants and Children

The same general principles for managing a normal pediatric airway apply to managing both an unexpected and an expected difficult pediatric airway (also see Chapter 34). It is unlikely that infants and children will cooperate with procedures, such as an awake fiberoptic endotracheal intubation. Therefore, it is often necessary to induce anesthesia and manage the airway with the patient asleep. Infants and children desaturate much more rapidly than adults because their oxygen consumption per kilogram is much higher than adults. This time constraint presents an additional challenge when managing both an unexpected and expected difficult airway in infants and children.

Unexpected Difficult Airway

When an unexpected difficult airway occurs in pediatric patients, the most important first step is to call for an additional anesthesia colleague to help (Fig.21), as well as a surgeon adept in surgical airway management if an emergent surgical airway is necessary. A pediatric difficult airway cart should be obtained. The contents should include additional airway equipment including appropriately sized video laryngoscopes, fiberoptic bronchoscopes, and supraglottic, nasal, and oral airways. It is critical that the anesthesia provider not persist with repeated attempts at direct laryngoscopy. This can result in trauma to the upper airway, edema, and bleeding. In most situations, a supraglottic airway device should be inserted to oxygenate and ventilate the patient, and allow time to obtain additional personnel and airway equipment. If blood or significant secretions are in the airway, a video laryngoscope is a better option than a pediatric fiberoptic bronchoscope for viewing the glottis and intubating the trachea. Using a supraglottic airway device as a conduit for fiberoptic intubation can provide a channel that minimizes blood and secretions and allows for successful fiberoptic intubation.

Expected Difficult Airway

An expected difficult airway in pediatric patients should be approached with caution. Only preanesthetic medications that have minimal ventilatory depressant effects, such as midazolam, should be used. These preanesthetic medications should be administered in a location with appropriate airway equipment, including suction and a method of delivering oxygen with positive pressure. Pulse oximetry monitoring should be initiated.

An additional anesthesia colleague should be available for help during the induction of anesthesia, inserting an IV line, and securing the airway. A surgeon capable of establishing a surgical airway and emergency airway equipment should be in the operating room before beginning the induction of anesthesia. The most difficult decision in managing an expected difficult pediatric airway is whether to attempt direct laryngoscopy or to proceed directly to an alternative strategy for managing the airway (i.e., supraglottic airway device, fiberoptic intubation, video laryngoscopy, or surgical airway). The history and physical examination may indicate situations in which direct laryngoscopy will not be successful, such as a patient in halo traction. In these cases, one should avoid direct laryngoscopy and proceed directly to an alternative strategy for managing the airway. As with the unexpected difficult airway, if direct laryngoscopy is not successful, one should not persist with direct laryngoscopy.

Tracheal Extubation in Infants and Children

Postextubation Croup

Infants and small children are at higher risk than adults for croup after endotracheal extubation. Croup occurs most commonly when an uncuffed endotracheal tube that is too large or a cuffed endotracheal tube that is overinflated is used. The resulting pressure on the tracheal mucosa causes venous congestion and edema. In severe cases, the arterial blood supply can be compromised, causing mucosal ischemia. The resulting edema can narrow the tracheal lumen, especially in pediatric patients. Because resistance to flow through the airway is inversely proportional to the radius of the lumen to the fourth power, 1 mm of edema in a pediatric airway is much more significant than 1 mm of edema in an adult airway. Other risk factors for croup include multiple endotracheal intubation attempts, unusual positioning of the head during surgery, increased duration of surgery, and procedures involving the upper airway, such as rigid bronchoscopy.

Manifestations

An infant or child with postextubation croup usually has respiratory distress in the postanesthesia care unit. Nasal flaring, retractions, an increased respiratory rate, audible stridor, and decreased oxygen saturation are common clinical findings.

Treatment

Treatment of postextubation croup depends on the degree of respiratory distress. Mild symptoms can be managed with humidified oxygen and prolonged observation in the postanesthesia care unit. Severe cases may require aerosolized racemic epinephrine and postoperative observation in an intensive care unit. Patients whose respiratory distress is severe and not relieved with these measures may need to be reintubated with a smaller endotracheal tube. To prevent upper airway edema, steroids (e.g., dexamethasone) should be administered intravenously before the airway is instrumented in procedures such as rigid bronchoscopy.

Obstructive Sleep Apnea

Infants and children with obstructive sleep apnea are at significant risk for airway obstruction, respiratory distress, and the potential for apnea in the postoperative period. At baseline, these infants and children hypoventilate, resulting in hypercapnia and often arterial hypoxemia when they sleep. Residual inhaled anesthetics or residual neuromuscular blockade can depress airway reflexes, decrease skeletal muscle tone and strength, and lower respiratory drive. This can result in significant airway compromise. Opioids must be very carefully titrated both intraoperatively and postoperatively, as they can depress the ventilatory drive and contribute to significant hypercapnia and arterial hypoxemia in these patients.

Tracheal extubation in patients with obstructive sleep apnea should occur only when they are fully awake. All infants and children with obstructive sleep apnea should be monitored postoperatively with pulse oximetry. High-risk patients should be monitored postoperatively in an intensive care unit setting.

Laryngospasm

Infants and children are more prone to laryngospasm than older children and adults. Laryngospasm most commonly occurs during either inhalational induction of anesthesia or emergence from anesthesia, often after extubation or removal of a supraglottic airway device. Most of laryngo-spasm episodes in pediatric patients can be treated successfully with continuous positive-pressure ventilation via face mask with 100% O2, while applying a chin lift and jaw thrust. The positive pressure may have to be as high as 50 cm H2O to successfully break the laryngospasm. If positive pressure is not successful and the infant or child is desaturating or bradycardic, further intervention is necessary. If there is IV access, laryngospasm should be treated with approximately 0.6 to 1.0 mg/kg of IV propo-fol and, if necessary, 0.2 to 0.3 mg/kg of IV rocuronium. If there is no IV access, laryngospasm should be treated with 0.6 to 1.0 mg/kg of intramuscular rocuronium or 1.5 to 2.0 mg/kg of intramuscular succinylcholine.(65)

Extubation After a Difficult Intubation

Tracheal extubation of an infant or child after a difficult intubation should be considered carefully because reintubation can be more difficult than the initial intubation. The tracheas of infants and children with difficult airways should be extubated only when the patient is fully awake and there is no residual neuromuscular blockade. They should be extubated only when appropriate equipment and personnel are available for urgent reintubation.

Postoperative factors that can further compromise respiratory function must also be considered when extubating the trachea of an infant or child with a difficult intubation. For example, postoperative pain, especially if there is splinting from an abdominal or thoracic incision, may compromise respiratory function. Postoperative pain requiring significant opioid use will also compromise breathing by decreasing the respiratory drive. The use of regional anesthesia, such as a caudal or an epidural, may allow earlier extubation of these patients.

Edema of the airway from surgical trauma, positioning, or excessive fluid administration can significantly affect the ability to extubate the tracheas of infants and children with difficult intubations and can make emergency reintubation more difficult. Infants and children with postoperative airway edema and difficult airways should remain intubated until the edema has resolved. Fiberoptic bronchoscopy is an excellent tool for examining the supraglottic airway in the intubated infant or child for determining whether there is any significant residual airway edema.

1.  What is the sensory and motor innervation of the larynx? What are the methods to provide topical anesthesia prior to awake fiberoptic intubation?
2. What physical examination findings predict difficult endotracheal intubation or difficult mask ventilation?
3. What are the risks and contraindications of using a supraglottic airway device instead of an endotracheal tube for airway management?
4. What are the advantages and disadvantages of video laryngoscopy versus conventional direct laryngoscopy or flexible fiberoptic laryngoscopy during routine airway management and difficult airway management?
5. What are the most important clinical differences in the following airway devices: plastic-coated metal endotracheal tube stylet, gum elastic bougie, and intubating stylet (e.g., Frova or Aintree)?
6. During a “cannot intubate, cannot ventilate” situation in which supraglottic airway placement has also failed, what are the relative advantages and disadvantages of cricothyrotomy versus transtracheal jet ventilation?
7. What are the most common complications after endotracheal extubation in adults and children? What is the expected time course of the complications?
8. What are the major differences between the airway anatomy of an infant compared to an adult?
9. When an uncuffed endotracheal tube is used in an infant, what steps should be taken to determine the appropriate size?

1. Apfelbaum JL, Hagberg CA, Caplan RA,et al. Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology. 2013;118(2):251–270.
2. Cook TM, MacDougall-Davis SR. Complications and failure of airway management. Br J Anaesth. 2012;109(suppl1):i68–i85.
3. Sahin-Yilmaz A, Naclerio RM. Anatomy and physiology of the upper airway. Proc Am Thorac Soc. 2011;8(1):31–39.
4. Ovassapian A. Fiberoptic Airway Endoscopy in Anesthesia and Critical Care. New York: Raven Press; 1990.
5. Stackhouse RA. Fiberoptic airway management. Anesthesiol Clin North Am. 2002;20(4):933–951.
6. Patil VU, Stehling LC, Zauder HL. Fiberoptic Endoscopy in Anesthesia. St. Louis: Mosby; 1983.
7. Isaacs RS, Sykes JM. Anatomy and physiology of the upper airway. Anesthesiol Clin North Am. 2002;20(4):733–745.
8. Cook TM, Woodall N, Frerk C. Fourth National Audit Project. Major complications of airway management in the UK: results of the fourth national audit
project of the royal college of anaesthetists and the difficult airway society. Part 1: anaesthesia. Br J Anaesth. 2011;106(5):617–631.
9. Shiga T, Wajima Z, Inoue T, Sakamoto A. Predicting difficult intubation in apparently normal patients: a meta-analysis of bedside screening test performance. Anesthesiology. 2005;103(2):429–437.

10. Baker P. Assessment before airway management. Anesthesiol Clin. 2015;33(2):257–278.
11. Khan ZH, Mohammadi M, Rasouli MR, et al. The diagnostic value of the upper lip bite test combined with sternomental distance, thyromental distance, and interincisor distance for prediction of easy laryngoscopy and intubation: a prospective study. Anesth Analg. 2009;109(3):822–824.
12. Mallampati SR, Gatt SP, Gugino LD, et al. A clinical sign to predict difficult tracheal intubation: a prospective study. Can Anaesth Soc J. 1985;32(4):429–434.
13. Samsoon G, Young J. Difficult tracheal intubation: a retrospective study. Anaesthesia. 1987;42(5):487–490.
14. Khan ZH, Kashfi A, Ebrahimkhani E. A comparison of the upper lip bite test (a simple new technique) with modified Mallampati classification in predicting difficulty in endotracheal intubation: a prospective blinded study. Anesth Analg. 2003;96(2):595–599.
15. El-Ganzouri AR, McCarthy RJ, Tuman KJ, et al. Preoperative airway assessment: predictive value of a multivariate risk index. Anesth Analg. 1996;82(6): 1197–1204.
16. Bellhouse CP, Dore C. Criteria for estimating likelihood of difficulty of endotracheal intubation with the Macintosh laryngoscope. Anaesth Intensive
Care. 1988;16(3):329–337.
17. Kheterpal S, Healy D, Aziz MF, et al. Incidence, predictors, and outcome of difficult mask ventilation combined with difficult laryngoscopy: a report from the multicenter perioperative outcomes group. Anesthesiology. 2013; 119(6):1360–1369.
18. Law JA, Broemling N, Cooper RM, et al. The difficult airway with recommendations for management—part 2—the anticipated difficult airway. Can J Anesth. 2013;60(11):1119–1138.
19. Law JA, Broemling N, Cooper RM, et al. The difficult airway with recommendations for management—part 1—difficult tracheal intubation encountered in an unconscious/induced patient. Can J Anesth. 2013;60(11):1089–1118.
20. El-Orbany M, Woehlck HJ. Difficult mask ventilation. Anesth Analg. 2009;109(6):1870–1880.
21. Benumof JL, Dagg R, Benumof R. Critical hemoglobin desaturation will occur before return to an unparalyzed state following 1 mg/kg intravenous succinylcholine. Anesthesiology. 1997;87(4):979–982.
22. Bouroche G, Bourgain JL. Preoxygenation and general anesthesia: a review. Minerva Anestesiol. 2015;81(8):910–920.
23. Dixon BJ, Dixon JB, Carden JR, et al. Preoxygenation is more effective in the 25 degrees head-up position than in the supine position in severely obese patients: a randomized controlled study. Anesthesiology. 2005;(102):1110–1115.
24. Futier E, Constantin JM, Pelosi P, et al. Noninvasive ventilation and alveolar recruitment maneuver improve respiratory function during and after intubation of morbidly obese patients: a randomized controlled study. Anesthesiology. 2011;114(6):1354–1363.

25. Hernandez MR, Klock Jr PA, Ovassapian A. Evolution of the extraglottic airway: a review of its history, applications, and practical tips for success. Anesth Analg. 2012;114(2):349–368.
26. Timmermann A. Supraglottic airways in difficult airway management: successes, failures, use and misuse. Anaesthesia. 2011;66(suppl 2):45–56.
27. Ramachandran SK, Mathis MR, Tremper KK, et al. Predictors and clinical outcomes from failed laryngeal mask airway unique: a study of 15,795 patients. Anesthesiology. 2012;116(6):1217–1226. 

28. Wong DT, Yang JJ, Jagannathan N. Brief review: the LMA supreme supraglottic airway. Can J Anesth J. 2012;59(5):483–493.
29. Cook T, Howes B. Supraglottic airway devices: recent advances. Contin Educ Anaesth Crit Care Pain. 2011;11(2):56–61.
30. Hagberg C. Current concepts in the management of difficult airway. Anesthesiol News. 2014;11(1):1–28.
31. Agro F, Frass M, Benumof JL, Krafft P. Current status of the Combitube: a review of the literature. J Clin Anesth. 2002;14(4):307–314.
32. Cormack R, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia. 1984;39(11):1105–1111.
33. McKeen DM, George RB, O’Connell CM, et al. Difficult and failed intubation: incident rates and maternal, obstetrical, and anesthetic predictors. Can J Anesth. 2011;58(6):514–524.
34. Griesdale DE, Liu D, McKinney J, Choi PT. Glidescope® video-laryngoscopy versus direct laryngoscopy for endotracheal intubation: a systematic review and meta-analysis. Can J Anesth. 2012;59(1):41–52.
35. Aziz MF, Dillman D, Fu R, Brambrink AM. Comparative effectiveness of the C-MAC video laryngoscope versus direct laryngoscopy in the setting of the predicted difficult airway. Anesthesiology. 2012;116(3):629–636.
36. Cooper RM. Strengths and limitations of airway techniques. Anesthesiol Clin. 2015;33(2):241–255.
37. Paolini J, Donati F, Drolet P. Review article: video-laryngoscopy: another tool for difficult intubation or a new paradigm in airway management? Can
J Anesth. 2013;60(2):184–191.
38. Aziz MF, Healy D, Kheterpal S, et al. Routine clinical practice effectiveness of the glidescope in difficult airway management: an analysis of 2,004
glidescope intubations, complications, and failures from two institutions. Anesthesiology. 2011;114(1):34–41.
39. Rosenstock CV, Thogersen B, Afshari A, et al. Awake fiberoptic or awake video laryngoscopic tracheal intubation in patients with anticipated difficult airway management: a randomized clinical trial. Anesthesiology. 2012;116(6):1210–1216.
40. Serocki G, Neumann T, Scharf E, et al. Indirect videolaryngoscopy with C-MAC D-blade and GlideScope: a randomized, controlled comparison in patients with suspected difficult airways. Minerva Anestesiol. 2013;79(2):121–129.
41. Duggan LV, Law JA, Murphy MF. Brief review: supplementing oxygen through an airway exchange catheter: efficacy, complications, and recommendations. Can J Anesth. 2011;58(6):560–568.
42. Simmons ST, Schleich AR. Airway regional anesthesia for awake fiberoptic intubation. Reg Anesth Pain Med. 2002;27(2):180–192.
43. Sengupta P, Sessler DI, Maglinger P, et al. Endotracheal tube cuff pressure in three hospitals, and the volume required to produce an appropriate cuff pressure. BMC Anesthesiol. 2004;4(1):8.
44. Smith KJ, Dobranowski J, Yip G, et al. Cricoid pressure displaces the esophagus: an observational study using magnetic resonance imaging. Anesthesiology. 2003;99(1):60–64.
45. Ovassapian A, Salem MR. Sellick’s maneuver: to do or not do. Anesth Analg. 2009;109(5):1360–1362.
46. Rice MJ, Mancuso AA, Gibbs C, et al. Cricoid pressure results in compression of the postcricoid hypopharynx: the esophageal position is irrelevant. Anesth Analg. 2009;109(5):1546–1552.
47. Schaumann N, Lorenz V, Schellongowski P, et al. Evaluation of Seldinger technique emergency cricothyroidotomy versus standard surgical cricothyroidotomy in 200 cadavers. J Am Soc Anesthesiol. 2005;102(1):7–11.
48. Kristensen MS, Teoh WH, Baker PA. Percutaneous emergency airway access; prevention, preparation, technique and training. Br J Anaesth.
2015;114(3):357–361.
49. Hamaekers A, Henderson J. Equipment and strategies for emergency tracheal access in the adult patient. Anaesthesia. 2011;66(suppl 2):65–80.
50. Ross-Anderson DJ, Ferguson C, Patel A. Transtracheal jet ventilation in 50 patients with severe airway compromise and stridor. Br J Anaesth. 2011;106(1):140–144.
51. Dhara SS. Retrograde tracheal intubation. Anaesthesia. 2009;64(10):1094–1104.
52. Mitchell V, Dravid R, Patel A, et al. Difficult airway society guidelines for the management of tracheal extubation. Anaesthesia. 2012;67(3):318–340.
53. Cavallone LF, Vannucci A. Review article: extubation of the difficult airway and extubation failure. Anesth Analg. 2013;116(2):368–383.

54. Warner ME, Benenfeld SM, Warner MA, et al. Perianesthetic dental injuries: frequency, outcomes, and risk factors. Anesthesiology. 1999;90(5):1302–1305.
55. Hagberg C, Georgi R, Krier C. Complications of managing the airway. Best Pract Res Clin Anaesthesiol. 2005;19(4):641–659.
56. Schloss B, Rice J, Tobias JD. The laryngeal mask in infants and children:what is the cuff pressure? Int J Pediatr Otorhinolaryngol. 2012;76(2):284–286.
57. Jagannathan N, Sohn L, Sommers K, et al. A randomized comparison of the laryngeal mask airway supreme and laryngeal mask airway unique in infants and children: does cuff pressure influence leak pressure? Pediatr Anesth. 2013;23(10):927–933.
58. Tobias JD, Schwartz L, Rice J, et al. Cuffed endotracheal tubes in infants and children: should we routinely measure the cuff pressure? Int J Pediatr
Otorhinolaryngol. 2012;76(1):61–63.
59. Weiss M, Dullenkopf A, Fischer JE, et al. European Paediatric Endotracheal Intubation Study Group. Prospective randomized controlled multi-centre trial of cuffed or uncuffed endotracheal tubes in small children. Br J Anaesth. 2009;103(6):867–873.
60. Litman RS, Maxwell LG. Cuffed versus uncuffed endotracheal tubes in pediatric anesthesia: the debate should finally end. Anesthesiology. 2013;118(3):500–501.
61. Liu J, Zhang X, Gong W, et al. Correlations between controlled endotracheal tube cuff pressure and postprocedural complications: a multicenter study. Anesth Analg. 2010;111(5):1133–1137.
62. Sathyamoorthy M, Lerman J, Lakshminrusimha S, Feldman D. Inspiratory stridor after tracheal intubation with a MicroCuff(R) tracheal tube in
three young infants. Anesthesiology. 2013;118(3):748–750.
63. Sun Y, Lu Y, Huang Y, Jiang H. Pediatric video laryngoscope versus direct laryngoscope: a meta-analysis of randomized controlled trials. Pediatr Anesth. 2014;24(10):1056–1065.
64. Fiadjoe JE, Gurnaney H, Dalesio N, et al. A prospective randomized equivalence trial of the GlideScope cobalt® video laryngoscope to traditional direct laryngoscopy in neonates and infants. Anesthesiology. 2012;116(3):622–628.
65. Orliaguet GA, Gall O, Savoldelli GL, Couloigner V. Case scenario: perianesthetic management of laryngospasm in children. Anesthesiology. 2012;116(2):458–471.

Authors: Kerry Klinger and Andrew Infosino