The primary goal of airway management is to provide adequate oxygenation and ventilation to a patient. Anesthesia providers become particularly skilled in the field of airway management as anesthetic drugs and techniques impair a patient’s ability to perform these vital functions on his or her own. The induction of anesthesia is a critical time period for a patient. During this time, patients become apneic (stop breathing) and rely on their anesthesia provider to perform these vital functions for them. Failure to restore oxygenation and ventilation is the gravest risk in anesthesiology as anoxic brain injury ensues and ultimately cardiac collapse and death. Preparation of the patient for safe and effective airway management is the key element of safety for an anesthesia provider. This chapter focuses on those principles.

Knowledge of the relevant airway anatomy is critical to safe airway management (see also Chapter 11). The key anatomic structures involved include the nose, pharynx, larynx, and trachea (Fig. 18.1). The nose functions to warm and humidify air. It is the primary route of breathing except for situations of obstruction or increased demand where the mouth can move air at a lower resistance. Placement of devices within the nose poses a significant risk of nosebleed. While blood loss is typically not severe, it can dramatically impair the ability to subsequently view the airway. This impaired view is most pronounced with the use of video techniques as blood smears the lens. Direct techniques can also be impaired with nasal bleeding.

The mouth (oropharynx) and throat (pharynx) provide another passageway to the lungs. In normal patients, breathing through the mouth is used when ventilation increases or when the nasal passage is obstructed. Anesthesia providers frequently place devices in the oropharynx to assist with ventilation or to view the larynx (laryngoscopy). Injury to the lips, tongue, and teeth is possible. The teeth are particularly problematic as laryngoscopes apply pressure to upper dentition when laryngoscopy is poorly performed or when view of the larynx is difficult to achieve. When a patient is anesthetized or sedated in the supine position (lying down), airway obstruction is common as the tongue falls back against the pharynx. This obstruction can be effectively relieved by pulling the mandible forward (jaw thrust) or inserting an oral airway to bring the tongue forward and off of the posterior pharynx.

The larynx is a structure of cartilage that supports phonation (speech). It includes the epiglottis, arytenoids cartilage, cricoid cartilage, thyroid cartilage (Adam’s apple), trachea, and vocal cords. An endotracheal tube is passed beyond the larynx and into the trachea for proper placement. A supraglottic airway (e.g., LMA^TM [laryngeal mask airway]) is positioned in the pharynx in such a way that the tip sits in the esophageal inlet and the lumen sits above the vocal cords.

The trachea is a round tissue structure supported by cartilage that extends from the larynx to the main bronchi. The carina is the cartilaginous structure at the bifurcation of the trachea to the bronchi. The trachea is lined with nerve fibers that are very sensitive to stimulation from gases or tracheal tubes. These receptors trigger cough or bronchospasm. The carina is particularly sensitive to stimulation. An endotracheal tube that is positioned too deep can either irritate the carina, causing cough and bronchospasm, or enter the bronchi (usually the right side). A tube improperly positioned in the right mainstem bronchus will cause hypoxia as ventilation is provided only to a portion of the lungs.

An endotracheal tube is placed for airway protection and/or the need for positive pressure ventilation. The airway requires protection from either aspiration of gastric contents or obstruction from an outside source of compression. Patients at risk for aspiration are those who are sedated, anesthetized, or intoxicated and have a full stomach from a recent meal or poor digestion. Patients with an empty stomach may still be at risk for aspiration if they have disease of the esophagus or abdominal pathology that slows digestion and increases stomach volume. Specific patient conditions that are commonly considered to be a higher aspiration risk include pregnancy, trauma, bowel obstruction, diabetes, and obesity.

The airway may also require protection from external compression. That compression can come in the form of a tumor mass, abscess, or hematoma (bleeding). The postsurgical patient
with bleeding in the neck is particularly concerning as the hematoma may expand rapidly to occlude a patient’s airway. Any form of external compression can make intubation of the trachea more technically challenging. Therefore, it is important to act quickly to secure an airway before the compression source grows and intubation becomes difficult and/or airway occlusion ensues.

The majority of intubations are performed because of the need for positive pressure ventilation. Under normal physiologic conditions, oxygen enters the chest through a negative pressure mechanism. The diaphragm contracts downward to expand the lungs and draw oxygen into them. Certain scenarios make this type of ventilation inadequate. Positive pressure reverses the physiology and instead pushes oxygen into the lungs. This pressure can be delivered via a face mask or a supraglottic airway device and most definitively, through an endotracheal tube. The patient under general anesthesia is exposed to drugs that suppress ventilatory effort, and positive pressure is often needed. The use of muscle relaxation (paralytics) makes patient-controlled ventilation (spontaneous ventilation) impossible and mandates positive pressure ventilation.

Certain patient conditions may also impair a patient’s ability to maintain negative pressure breathing and thus require positive pressure ventilation through an endotracheal tube. Neurologic conditions such as stroke and neuromuscular disease cause weakness that may become severe enough to require positive pressure ventilation. More commonly, diseases of the lung make the added work of breathing difficult and a patient may fatigue in his or her effort to improve ventilation. In intensive care units, diseases such as pneumonia, pneumothorax, or pulmonary fibrosis may result in conditions of impaired oxygenation and ventilation that can only be overcome with positive pressure ventilation delivered via an endotracheal tube.

The gravest risk in airway management is the inability or failure to intubate a patient who requires it. This failure may be recognized or unrecognized. The development of in-line CO₂ monitoring has changed the field of anesthesia and dramatically reduced the occurrence of unrecognized esophageal intubation. Today, failure more commonly occurs in a recognized situation. The consequence of failure to intubate can be severe if other means to oxygenate (mask ventilation) fail or are attempted too late. This risk is particularly important in anesthesia as the medications used to facilitate intubation impair the patient’s ability to ventilate.

More commonly observed complications are related to trauma during the process of laryngoscopy. Lip lacerations are the most common form of injury but rarely result in long-standing problems. Dental injury is a common occurrence as laryngoscope blades make contact with the upper incisors. These injuries are the most common source of litigation against anesthesia providers. Depending on the route of intubation (oral vs. nasal), trauma can occur anywhere along the course of the tracheal tube including the vocal cords and nerves to the vocal cords. These injuries can result in temporary or permanent voice problems.

Another complication associated with intubation is related to hemodynamics. Placement of a tracheal tube is remarkably stimulating to an awake or even an anesthetized patient. Commonly, there is a dramatic rise in heart rate and blood pressure if active measures are not taken to blunt these responses. The gravest risk of this heart rate and blood pressure response is stress on the heart, which may cause a myocardial infarction, or rupture of a blood vessel in the brain, leading to stroke. Detailed knowledge of the patient’s preexisting medical problems helps the anesthesiologist optimize an anesthetic induction drug cocktail to balance the effects of the stimulation of intubation with the relative depressant effects of anesthesia induction drugs.

Laryngospasm is a complication that is often seen before or after tracheal tube placement. A partially anesthetized airway that is irritated from instrumentation, blood, or secretions is prone to spastic closure. This closure can make airway movement impossible, even if the patient retains respiratory effort. If left untreated, patient breathing against a closed larynx can draw fluid into the lung cavity (pulmonary edema). In addition, laryngospasm can last long enough that the patient can become hypoxic. Recognition of this obstructed breathing pattern is important as rapid action can prevent dangerously low blood oxygen content. Application of positive pressure
through a face mask can “break” the laryngospasm. If this treatment fails, a rapidly acting paralytic should be given to relax the vocal cords.

The consequences of failure to ventilate are so severe; it is critical to anticipate the potential difficult airway and craft an airway management plan that is safe and comfortable for the patient. The strongest predictor of difficulty is a history of difficult airway management. Anesthesia providers must predict the difficulty of both failed bag-mask ventilation and failed intubation. Unfortunately, the available bedside testing measures for predicting difficult intubation or ventilation have a poor predictive value. In other words, intubation may fail even with patients who are predicted to be easy. Conversely, a patient with multiple predictors of difficulty may be fairly easy to intubate.

Bag-mask ventilation is made more difficult by several patient conditions. Commonly, the obese patient presents difficulty as soft tissue in the pharynx collapses under anesthesia or sedation. Other predictors of difficult bag-mask ventilation include older age, presence of a beard, lack of teeth, history of neck radiation, high Mallampati classification scale score (see below), and history of obstructive sleep apnea.

Difficult intubation can be predicted by several bedside examinations. The risk of failed intubation rises with a greater number of predictors present. The most commonly referenced bedside examination tool is the Mallampati classification score (Fig. 18.2). This bedside test correlates a patient’s mouth opening to tongue size to derive a scale of 1-4, with a score of 4 predicting the most difficulty. Other measurements that predict difficulty are a small mouth opening, small distance from the thyroid cartilage to the chin, reduced neck mobility, inability to protrude the jaw forward, neck mass, and large neck circumference. The presence of obesity as a predictor of difficult intubation is debated in the literature. A high body mass index may not make intubation more difficult if a patient is properly positioned. However, a large neck circumference is associated with intubation difficulty. Appropriate positioning of an obese patient in a “ramped” position improves the adequacy of mask ventilation and eases intubation. Despite these concerns, the obese patient is at particular risk of grave consequences if intubation fails as bag-mask ventilation may be more difficult, aspiration risk is higher, and oxygen saturation falls more quickly.

Beyond the bedside exam, patient history predicts difficulty. Patients with pathology of the neck can be very difficult to intubate. Neck trauma, masses in the neck area, infection around the neck, previous neck radiation, and disease of the spine can make both mask ventilation and intubation difficult.

After appropriate room setup, preparation of devices, and monitoring, an adult patient is typically preoxygenated. The purpose of this step is to “buy time” after anesthesia induction and anticipated apnea. Preoxygenation is effectively achieved by supplying 100% oxygen via a face mask on a circuit with reservoir (anesthesia machine, Jackson-Reese). After 3 minutes of normal breathing or five full capacity breaths, the nitrogen in the lungs is replaced by oxygen. With the lungs full of oxygen, an anesthetized patient will consume the oxygen in the lungs for several minutes before blood oxygen levels fall. Some patient conditions are more prone to a rapid fall of oxygen levels (desaturation). These conditions include infancy, obesity, pregnancy, and poor baseline lung gas exchange.

After preoxygenation, anesthetic induction is typically performed with intravenous
(IV) agents in adults or inhalational agents in children. Muscle relaxation (paralysis) is commonly employed to facilitate intubation as intubation success improves with use of paralytics. These drugs offer the benefit of easier intubation but carry risks as the patient becomes apneic and will not restore ventilation again until the induction drugs and paralytics have appropriately been metabolized or reversed. Therefore, paralytic medication should be used very cautiously in the anticipated difficult airway.