1 List several indications for endotracheal intubation

General anesthesia but there are alternatives to endotracheal intubation

Positive-pressure ventilation

Protecting the respiratory tract from aspiration of gastric contents

Surgical procedures in which the anesthesiologist cannot easily control the airway (e.g., prone, sitting, or lateral decubitus procedures)

Situations in which neuromuscular paralysis has been instituted

Surgical procedures within the chest, abdomen, or cranium

When intracranial hypertension must be treated

Protecting a healthy lung from a diseased lung to ensure its continued performance (e.g., hemoptysis, empyema, pulmonary abscess)

Severe pulmonary and multisystem injury associated with respiratory failure (e.g., severe sepsis, airway obstruction, hypoxemia, and hypercarbia of various etiologies)

2 Review objective measures suggesting the need to perform endotracheal intubation

These objective measures are often used for patients in critical-care settings, not necessarily perioperatively. But they also are useful in determining which patients should not be extubated after surgery.

Respiratory rate >35 breaths/min

Vital capacity <5 ml/kg in adults and 10 ml/kg in children

Inability to generate a negative inspiratory force of 20 mm Hg

Arterial partial pressure of oxygen (PaO₂) <70 mm Hg on 40% oxygen

Alveolar-arterial (A-a) gradient >350 mm Hg on 100% O₂

Arterial partial pressure of carbon dioxide (PaCO₂) >55 mm Hg (except in chronic retainers)

Dead space (Vd/Vt) >0.6

3 What historical information might be useful in assessing a patient’s airway?

Patients should be questioned about adverse events related to previous airway management episodes. For instance, have they ever been informed by an anesthesiologist that they had an airway management problem (e.g., “difficult to ventilate, difficult to intubate”)? Have they had a tracheostomy or other surgery or radiation about the face and neck? Have they sustained significant burns to these areas? Do they have obstructive sleep apnea, snoring, or temporomandibular joint (TMJ) dysfunction? Review of prior anesthetic records is always helpful.

4 Describe the physical examination of the oral cavity

Examine the mouth and oral cavity, noting the extent and symmetry of opening (three fingerbreadths is optimal), the health of the teeth (loose, missing, or cracked teeth should be documented), and the presence of dental appliances. Prominent buck teeth may interfere with the use of a laryngoscope. The size of the tongue should be noted (large tongues rarely make airway management impossible, only more difficult), as should the arch of the palate (high-arched palates have been associated with difficulty in visualizing the larynx).

5 Review the Mallampati classification

The appearance of the posterior pharynx may predict difficulty in laryngoscopy and visualization of the larynx. It has been noted through meta-analysis that, when used alone, the Mallampati test has limited accuracy for predicting the difficult airway and thus it is clear that a comprehensive airway examination, not just a Mallampati classification, is necessary to identify patients who may be difficult to intubate. This classification also does not address the issue of ease of mask ventilation.

Mallampati has organized patients into classes I to IV based on the visualized structures (Figure 8-1). Visualization of fewer anatomic structures (particularly classes III and IV) is associated with difficult laryngeal exposure. With the patient sitting upright, mouth fully open, and tongue protruding, classification is based on visualization of the following structures:

Class I: Pharyngeal pillars, entire palate, and uvula are visible.

Class II: Pharyngeal pillars and soft palate are visible, with visualization of the uvula obstructed by the tongue.

Class III: Soft palate is visible, but pharyngeal pillars and uvula are not visualized.

Class IV: Only the hard palate is visible; the soft palate, pillars, and uvula are not visualized.

Figure 8-1 Mallampati classification of the oropharynx.

6 What is the next step after examination of the oral cavity?

After examination of the oral cavity is completed, attention is directed at the size of the mandible and quality of TMJ function. A short mandible (shorter than three fingerbreadths) as measured from the mental process to the prominence of the thyroid cartilage (thyromental distance) suggests difficulty in visualizing the larynx. Patients with TMJ dysfunction may have asymmetry or limitations in opening the mouth and popping or clicking. Manipulation of the jaw in preparation for laryngoscopy may worsen symptoms after surgery. Curiously some patients with TMJ dysfunction have greater difficulty opening the mouth after anesthetic induction and neuromuscular paralysis than when they are awake and cooperative.

7 Describe the examination of the neck

Evidence of prior surgeries (especially tracheostomy) or significant burns is noted. Does the patient have abnormal masses (e.g., hematoma, abscess, cellulitis or edema, lymphadenopathy, goiter, tumor, soft-tissue swelling) or tracheal deviation? A short or thick neck may prove problematic. A neck circumference of greater than 18 inches has been reported to be associated with difficult airways. Large breasts (e.g., a parturient) may make using the laryngoscope itself difficult, and short-handled laryngoscope handles have been developed with this in mind.

It is also important to have the patient demonstrate the range of motion of the head and neck. Preparation for laryngoscopy requires extension of the neck to facilitate visualization. Elderly patients and patients with cervical fusions may have limited motion. Furthermore, patients with cervical spine disease (disk disease or cervical instability, as in rheumatoid arthritis) may develop neurologic symptoms with motion of the neck. Radiologic views of the neck in flexion and extension may reveal cervical instability in such patients.

It is my experience that the preoperarative assessment of range of motion in patients with prior cervical spine surgery does not equate well with their mobility after anesthetized and paralyzed, suggesting that in this patient group wariness is the best policy and advanced airway techniques, as will be described, should be considered.

Particularly in patients with pathology of the head and neck such as laryngeal cancer, it is valuable to know the results of nasolaryngoscopy performed by otolaryngologists. (This is always the case in ear, nose, and throat surgery—never assume anything. Always work closely and preemptively with the surgeon to determine how the airway should be managed.) Finally, if history suggests dynamic airway obstruction (as in intrathoracic or extrathoracic masses), pulmonary function tests, including flow-volume loops, may alert the clinician to the potential for loss of airway once paralytic agents are administered.

8 Discuss the anatomy of the larynx

The larynx, located in adults at cervical levels 4 to 6, protects the entrance of the respiratory tract and allows phonation. It is composed of three unpaired cartilages (thyroid, cricoid, and epiglottis) and three paired cartilages (arytenoid, corniculate, and cuneiform). The thyroid cartilage is the largest and most prominent, forming the anterior and lateral walls. The cricoid cartilage is shaped like a signet ring, faces posteriorly, and is the only complete cartilaginous ring of the laryngotracheal tree. The cricothyroid membrane connects these structures anteriorly. The epiglottis extends superiorly into the hypopharynx and covers the entrance of the larynx during swallowing. The corniculate and cuneiform pairs of cartilages are relatively small and do not figure prominently in the laryngoscopic appearance of the larynx or in its function. The arytenoid cartilages articulate on the posterior aspect of the larynx and are the posterior attachments of the vocal ligaments (or vocal cords). Identification of the arytenoid cartilages may be important during laryngoscopy. In a patient with an anterior airway the arytenoids may be the only visible structures. Finally the vocal cords attach anteriorly to the thyroid cartilage.

9 Describe the innervation and blood supply to the larynx

The superior and recurrent laryngeal nerves, both branches of the vagus nerve, innervate the larynx. The superior laryngeal nerves decussate into internal and external branches. The internal branches provide sensory innervation of the larynx above the vocal cords, whereas the external branches provide motor innervation to the cricothyroid muscle, a tensor of the vocal cords. The recurrent laryngeal nerves provide sensory innervation below the level of the cords and motor innervation of the posterior cricoarytenoid muscles, the only abductors of the vocal cords. The glossopharyngeal or ninth cranial nerve provides sensory innervation to the vallecula (the space anterior to the epiglottis) and the base of the tongue.

Arteries that supply the larynx include the superior laryngeal (a branch of the superior thyroid artery) and inferior laryngeal (a branch of the inferior thyroid artery). Venous drainage follows the same pattern as the arteries; there is also ample lymphatic drainage.

10 Summarize the various instruments available to facilitate oxygenation

Oxygen supplementation is always a priority when patients are sedated or anesthetized. Devices range from nasal cannulas, face tents, and simple masks to masks with reservoirs and masks that can be used to deliver positive-pressure ventilation. Their limitation is the oxygen concentration that can be delivered effectively.

11 What are the benefits of oral and nasal airways?

Oral airways are usually constructed of hard plastic; they are available in numerous sizes and shaped to curve behind the tongue, lifting it off the posterior pharynx. The importance of these simple devices cannot be overstated because the tongue is the most frequent cause of airway obstruction, particularly in obtunded patients. Nasal airways (trumpets) can be gently inserted down the nasal passages into the nasopharynx and are better tolerated than oral airways in awake or lightly anesthetized patients. However, epistaxis is a risk.

12 How are laryngoscopes used?

Laryngoscopes are usually left-handed tools designed to facilitate visualization of the larynx. Short handles work best for obese patients or those with thick chests or large breasts. Laryngoscope blades come in various styles and sizes. The most commonly used blades include the curved Macintosh and the straight Miller blades. The curved blades are inserted into the vallecula, immediately anterior to the epiglottis, which is literally flipped out of the visual axis to expose the laryngeal opening. The Miller blade is inserted past the epiglottis, which is simply lifted out of the way of laryngeal viewing.

13 What structures must be aligned to accomplish visualization of the larynx?

To directly visualize the larynx it is necessary to align the oral, pharyngeal, and laryngeal axes. To facilitate this process, elevating the head on a small pillow and extending the head at the atlanto-occipal axes are necessary (Figure 8-2).

Figure 8-2 Schematic diagram demonstrating the head position for endotracheal intubation. A, Successful direct laryngoscopy for exposure of the glottic opening requires alignment of the oral, pharyngeal, and laryngeal axes. B, Elevation of the head about 10 cm with pads below the occiput and with the shoulders remaining on the table aligns the laryngeal and pharyngeal axes. C, Subsequent head extension at the atlanto-occipital joint creates the shortest distance and most nearly straight line from the incisor teeth to glottic opening.

(From Gal TJ: Airway management. In Miller RD: Miller’s anesthesia, ed 6, Philadelphia, 2005, Churchill Livingstone, p 1622.)

14 What is a GlideScope?

Different laryngoscope blades have been discussed, and it should be no surprise that various arrangements of laryngoscope handles and blades have been developed. The GlideScope Video Laryngoscope (Verathon, Inc., Bothell, WA) has a one-piece rigid plastic handle and curved blade; at the tip of the blade is not only the light but a camera eye. The image is transmitted to a screen at bedside. By using the GlideScope, it has not been necessary to align the three axes as discussed in the prior question. Thus the patient might easily be intubated with the neck in a neutral position. In addition, in patients in whom, on conventional laryngoscopy, the laryngeal aperture is anterior to the visual axis, the GlideScope facilitates visualization of the larynx and endotracheal intubation. The GlideScope has proven to be an outstanding addition to the airway management armamentarium.

15 What endotracheal tubes are available?

Endotracheal tubes come in a multitude of sizes and shapes. They are commonly manufactured from polyvinyl chloride, with a radiopaque line from top to bottom; standard-size connectors for anesthesia circuits or resuscitation bags; a high-volume, low-pressure cuff and pilot balloon; and a hole in the beveled, distal end (the Murphy eye). Internal diameter ranges from 2 to 10 mm in half-millimeter increments. Endotracheal tubes may be reinforced with wire, designed with laser applications in mind, or unusually shaped so they are directed away from the surgical site (oral or nasal RAE tubes).

16 What are laryngeal mask airways?

Laryngeal mask airways (LMAs) maintain a patent airway during anesthesia when endotracheal intubation is neither required nor desired (e.g., asthmatic patients, the lead soprano in the local opera company). Increasingly LMAs are being substituted for endotracheal tubes. They are an important part of the management of difficult airways and patients can be intubated through a well-placed LMA.

17 What other airway management devices are available?

Light wands may be useful for blind intubation of the trachea. The technique is termed blind because the laryngeal opening is not seen directly. When light is well transilluminated through the neck (the jack-o’-lantern effect), the end of the endotracheal tube is at the entrance of the larynx, and the tube can be threaded off the wand and into the trachea in a blind fashion. Gum elastic bougies are flexible, somewhat malleable stylets with an anteriorly directed, bent tip that may be useful for intubating a tracheal opening anterior to the visual axis. Fiberoptic endoscopy is commonly used to facilitate difficult intubations and allows endotracheal tube insertion under direct visualization. Finally the trachea may be intubated using a retrograde technique. In simplistic terms a long Seldinger-type wire is introduced through a catheter that punctures the cricothyroid membrane. The wire is directed superiorly and brought out through the nose or mouth, and an endotracheal tube is threaded over the wire and lowered into the trachea.

18 Describe the indications for an awake intubation

If the physical examination leaves in question the ability to ventilate and intubate once the patient is anesthetized and paralyzed, consideration should be given to awake intubation. Patients with a previous history of difficult intubation, acute processes that compromise the airway (e.g., soft-tissue infections of the head and neck, hematomas, mandibular fractures, or other significant facial deformities), morbid obesity, or cancer involving the larynx are reasonable candidates for awake intubation.

19 How is the patient prepared for awake intubation?

A frank discussion with the patient is necessary because patient safety is the priority. The anticipated difficulty of airway management and the risks of proceeding with anesthesia without previously securing a competent airway are conveyed in clear terms. Despite our best efforts to provide topical anesthesia and sedation, sometimes the procedure is uncomfortable for the patient, and this should be discussed as well.

20 How is awake intubation performed?

In preparing the patient, administration of glycopyrrolate, 0.2 to 0.4 mg 30 minutes before the procedure, is useful to reduce secretions. Many clinicians also administer nebulized lidocaine to provide topical anesthesia of the entire airway, although many techniques are available to provide airway anesthesia. Once the patient arrives in the operating suite, standard anesthetic monitors are applied, and supplemental oxygen is administered. The patient is sedated with appropriate agents (e.g., opioid, benzodiazepine, propofol). The level of sedation is titrated so the patient is not rendered obtunded, apneic, or unable to protect the airway (Table 8-1).

The route of intubation may be oral or nasal, depending on surgical needs and patient factors. If nasal intubation is planned, nasal and nasopharyngeal mucosa must be anesthetized; vasoconstrictor substances are applied to prevent epistaxis. Often nasal trumpets with lidocaine ointment are gently inserted to dilate the nasal passages. A transtracheal injection of lidocaine is often performed via needle puncture of the cricothyroid membrane. Nerve blocks are also useful to provide topical anesthesia (see the following question).

Once an adequate level of sedation and topical anesthesia is achieved, the endotracheal tube is loaded on the fiberoptic endoscope. The endoscope is gently inserted into the chosen passage, directed past the epiglottis, through the larynx, into the trachea, visualizing tracheal rings and carina. The endotracheal tube is passed into the trachea, and the endoscope is removed. Breath sounds and end-tidal carbon dioxide are confirmed, and general anesthesia is begun.

21 What nerve blocks are useful when awake intubation is planned?

The glossopharyngeal nerve, which provides sensory innervation to the base of the tongue and the vallecula, may be blocked by transmucosal local anesthetic injection at the base of the tonsillar pillars. The superior laryngeal nerve provides sensory innervation of the larynx above the vocal cords and may be blocked by injection just below the greater cornu of the hyoid. Care must be taken to aspirate before injection because this is carotid artery territory. Many clinicians are reluctant to block the superior laryngeal nerves and perform a transtracheal block in patients with a full stomach because all protective airway reflexes are lost. Such patients are unable to protect themselves from aspiration if gastric contents are regurgitated.

22 What are predictors of difficult mask ventilation? Why is this important?

There is much focus on intubation and predictors of difficult intubation. It should be recognized that the ability to mask-ventilate a patient is equally and perhaps more important. For instance, if it is determined at the time of intubation that perhaps a patient is impossible to intubate by conventional laryngoscopy, if the patient’s oxygen saturations can be maintained through mask ventilation, the situation remains under a degree of control while help and additional airway management tools are summoned. However, if you have a patient who is difficult to intubate and ventilate, the situation is not under control, and the patient is at risk for hypoxic injury.

Between 1% and 2% of patients will be difficult to ventilate. Predictors of difficult mask ventilation include limitations in mandibular protrusion; a thyromental distance less than 6 cm; advanced age (older than 57 years in one study); abnormal neck anatomy; sleep apnea, snoring; body mass index of 30 kg/m² or greater; and the presence of a beard. A beard may in of itself make mask ventilation difficult, but it may also hide a small thyromental distance. Some men may choose to wear a beard because they don’t care for their weak chin facies, which is another way of saying that they have a small thyromental distance.

23 The patient has been anesthetized and paralyzed, but the airway is difficult to intubate. Is there an organized approach to handling this problem?

The patient who is difficult to ventilate and intubate is quite possibly the most serious problem faced by anesthesiologists because hypoxic brain injuries and cardiac arrest are real possibilities in this scenario. It has been established that persistent failed intubation attempts are associated with death. Although a thorough history and physical examination are likely to identify the majority of patients with difficult airways, unanticipated problems occasionally present. Only through preplanning and practiced algorithms are such situations managed optimally. The American Society of Anesthesiologists has prepared a difficult airway algorithm (Figure 8-3) to assist the clinician. The relative merits of different management options (surgical vs. nonsurgical airway, awake vs. postinduction intubation, spontaneous vs. assisted ventilation) are weighed. Once these decisions have been made, primary and alternative strategies are laid out to assist in stepwise management. This algorithm deserves close and repeated inspection before the anesthesiologist attempts to manage such problems. This is no time for heroism; if intubation or ventilation is difficult, call for help.

It is always wise to consider the merits of regional anesthesia to avoid a known or suspected difficult airway. However, in patients with a difficult airway, the use of regional anesthesia does not relieve the anesthesiologist of some planning for airway difficulties.

Death and central nervous system injuries remain the leading cause of adverse outcomes in the perioperative setting. However, it has been noted through analysis of closed medicolegal claims that the incidence of these injuries has decreased since these algorithms and advanced airway techniques have been introduced.

24 Describe the technique of transtracheal ventilation and its limitations

Transtracheal ventilation is a temporizing measure if mask ventilation becomes inadequate. A catheter (12- or 14-G) is inserted through the cricothyroid membrane and then connected to a jet-type (Sanders) ventilator capable of delivering oxygen under pressure. The gas is delivered intermittently by a handheld actuator. The duration of ventilation is best assessed by watching the rise and fall of the chest; an inspiratory to expiratory ratio of 1:4 seconds is recommended. Usually oxygenation improves rapidly; however, patients frequently cannot expire fully, perhaps because of airway obstruction, and can develop increased intrathoracic pressures, putting them at risk for barotrauma or decreased cardiac output. Carbon dioxide retention limits the duration of the usefulness of the technique.

25 What are criteria for extubation?

The patient should be awake and responsive with stable vital signs. Adequate reversal of neuromuscular blockade must be established as demonstrated by sustained head lift. In equivocal situations negative inspiratory force should exceed 20 mm Hg (see Question 2).

26 What is rapid-sequence induction? Which patients are best managed in this fashion?

It is easiest to appreciate the distinctions of rapid-sequence induction (RSI) if an induction under nonrapid-sequence conditions is understood. Ordinarily the patient has fasted for at least 6 to 8 hours and is not at risk for pulmonary aspiration of gastric contents. The patient is preoxygenated, and an anesthetic induction agent is administered. Once it is established that the patient can be mask-ventilated satisfactorily, a muscle relaxant is given. The patient is then mask-ventilated until complete paralysis is ensured by nerve stimulation. Laryngoscopy and endotracheal intubation are undertaken, and the case proceeds.

In contrast, RSI is undertaken in patients who are thought to be at risk for pulmonary aspiration of gastric contents. Patients with full stomachs are at risk; other risk factors include pregnancy, diabetes, pain, opioid analgesics, recent traumatic injury, intoxication, and pathologic involvement of the gastrointestinal tract such as small bowel obstruction. Patients with full stomachs should be premedicated with agents that reduce the acidity and volume of gastric contents such as histamine-2 receptor blockers (ranitidine, cimetidine), nonparticulate antacids (Bicitra or Alka-Seltzer), and gastrokinetics (metoclopramide).

27 How is RSI performed?

The goal of RSI is to secure and control the airway rapidly. The patient is preoxygenated. An induction agent is administered, followed quickly by a rapid-acting relaxant, either succinylcholine or larger doses of rocuronium. Simultaneously an assistant applies pressure to the cricoid cartilage (the only complete cartilaginous ring of the respiratory tract), which closes off the esophagus and prevents entry of regurgitated gastric contents into the trachea and lungs. Known as the Sellick maneuver, such pressure is maintained until the airway is protected by tracheal intubation.

28 What is the purpose of preoxygenation before the induction of anesthesia?

Preoxygenation is an important part of any general anesthetic. Inspired room air contains approximately 21% O₂, with the remainder being mostly nitrogen (N₂). Not many people can go more than a few minutes without ventilation before desaturation occurs. If patients breathe 100% oxygen for several minutes, they may not desaturate for up to 3 to 5 minutes because the functional residual capacity (FRC) of the lung has been completely washed of N₂ and filled with O₂.

29 Anesthesiologists routinely deliver 100% oxygen for a few minutes before extubation. What is the logic behind this action and why might an FiO₂ of 80% be better?

Patients emerging from general anesthesia may develop airway obstruction or disorganized breathing patterns. A 5-minute period of inspiring 100% oxygenation is sufficient to fill the patient’s FRC with 100% oxygen, establishing a depot of oxygen should airway obstruction or other respiratory difficulties accompany extubation. Unfortunately 100% oxygen promotes atelectasis, reducing the surface area available for gas exchange and causing intrapulmonary shunting. Although an FiO₂ of 0.8 appears to prevent atelectasis, it is not clear whether the small increase in atelectasis associated with breathing 100% oxygen is of clinical importance. Until this is demonstrated, the best practice is to administer 100% oxygen before extubation.