The decision to intubate can be a complex decision based on myriad factors that are in constant evolution. These factors include the patient’s vital signs, degree of respiratory distress, predicted clinical course, availability of definitive care, difficult airway tools, operator skill, or the need for transfer. In the emergency department (ED) and the intensive care unit (ICU), the implementation of Rapid sequence intubation (RSI) moved the decision to intubate by adding invaluable tools that have now been shown to reduce complications and improve the safety of intubation. RSI allows clinicians to be proactive with emergency airway management rather than waiting until they are obtunded. The advent of video laryngoscopy has changed decision making around how to intubate some patients with predicted difficulty, and our evolving understanding of the physiologic difficult airway is contributing to the change from Airway-Breathing-Circulation to Breathing-Circulation-Airway (or Circulation-Breathing-Airway, depending on the circumstance). Finally, noninvasive respiratory support strategies are an incredible tool to support work of breathing and gas exchange in patients that would otherwise require intubation early—moving the needle on the decision to intubate. What has not changed, however, is the critical importance of determining whether a patient requires intubation and, if so, how urgently. This is the first step in airway management and sets in motion a complex series of actions required by the clinician before performing the actual intubation:

Clinicians must be proficient with the techniques and medications used for RSI, the preferred method for most intubations, as well as alternative intubation strategies when induction and neuromuscular blockade are contraindicated or failed. Airway management requires proficiency (at a minimum) with the following skills: bag-mask ventilation, laryngoscopy (video laryngoscopy, direct laryngoscopy, and flexible endoscopy) with the use of adjuncts such as the tracheal tube introducer (also known as the gum elastic bougie), and rescue oxygenation which includes extraglottic devices and surgical airway techniques. This chapter focuses on the decision to intubate. Developing a strategy, methods, and peri-intubate optimization are discussed in subsequent chapters.

The decision to intubate is based on three fundamental clinical assessments:

The results of these three evaluations will lead to a correct decision to intubate or not to intubate in virtually all conceivable cases.

Without a patent airway and intact protective reflexes, adequate oxygenation and ventilation may be difficult or impossible and aspiration of gastric contents can occur. Both expose the patient to significant morbidity and mortality. The conscious, alert patient uses the musculature of the upper airway and various protective reflexes to maintain patency and to protect against aspiration of foreign substances, blood, gastric contents, or secretions. The patient’s ability to phonate with a clear, unobstructed voice is strong evidence of airway patency, protection, and cerebral perfusion. In severely ill or injured patients, such airway maintenance and protection mechanisms are often attenuated or lost.

If the spontaneously breathing patient is not able to maintain a patent airway, an artificially patent airway may be established by inserting an oropharyngeal or nasopharyngeal airway. Although these devices may restore patency, they do not provide any protection against aspiration. Patients who are unable to maintain their own airway are also unable to protect it. Therefore, generally, any patient who requires placement or tolerates the presence of an artificial airway also requires protection of that airway. The exception is when a patient has an immediately reversible cause of airway compromise (e.g., overdose) and reversing the insult promptly restores the patient’s ability to maintain an open, functioning airway. Airway protection requires a definitive airway (i.e., a cuffed endotracheal tube). Thus, devices that maintain airway patency but do not protect the airway, such as oropharyngeal or nasopharyngeal airways, are temporizing measures only. Supraglottic airway devices do provide some degree of airway protection but are still only temporary devices.

The gag reflex is commonly assessed and taught as a reliable method of evaluating airway protective reflexes. However, this concept has never been subjected to adequate scientific scrutiny, and the absence of a gag reflex is neither sensitive nor specific as an indicator of loss of airway protective reflexes. The patient’s Glasgow Coma Scale (GCS) is a better predictor of airway protection and their aspiration risk in overdose.¹ The presence of a gag reflex has similarly not been demonstrated to ensure the presence of airway protection. The gag reflex is a single limb afferent-efferent reflex and does not require a higher level of coordination like swallowing does. In addition, testing the gag reflex in an obtunded supine patient may result in vomiting and aspiration. Therefore, gag reflex testing has no clinical value, may be dangerous, and should not be used to assess the need for intubation.

Spontaneous or volitional swallowing is a better assessment of the patient’s ability to protect the airway. Swallowing is a complex reflex that requires the patient to sense the presence of material in the posterior oropharynx and then execute a series of intricate and coordinated muscular actions to direct the secretions down past a covered airway into the esophagus. The finding of pooled secretions in the patient’s posterior oropharynx indicates a potential failure of these protective mechanisms, and hence a failure of airway protection. A common clinical error is to assume that spontaneous breathing is proof that protective airway mechanisms are preserved. Although spontaneous ventilation may be adequate, the patient may be sufficiently obtunded to be at serious risk of aspiration.

Stated simply, gas exchange is required for vital organ function. Even brief periods of hypoxia should be avoided, whenever possible. If the patient is unable to ventilate sufficiently, or oxygenation is inadequate despite maximized supplemental oxygen, then intubation is indicated. In such cases, intubation is performed to improve gas exchange rather than to establish or protect the airway. An example is the patient with status asthmaticus, for whom bronchospasm and fatigue lead to ventilatory failure and hypoxemia, heralding respiratory arrest and death. Intubation is indicated when the patient will not respond sufficiently to optimal treatment efforts to reverse these cascading events. Similarly, patients with Acute respiratory distress syndrome (ARDS) may have progressive oxygenation failure and supervening fatigue that can be managed only with tracheal intubation and positive-pressure ventilation. On contrary, however, a patient with diabetic ketoacidosis may have ventilatory failure and acidemia, but intubation and mechanical ventilation will
not improve alveolar ventilation and may, in fact, make it worse unless the patient is obtunded or near respiratory arrest. A patient with a pulmonary embolism may have hypoxemia, but intubation will not improve the gas exchange and, again, may make it worse by worsening right ventricular function.