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  The choice between noninvasive ventilation via mask versus ventilation via translaryngeal tracheal intubation is an increasingly critical branch point in the management of patients with respiratory failure.

  
  
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  Shock, a failed trial of extubation, inability to protect and maintain one’s own airway, need for larger minute ventilations or larger transpulmonary pressures, and transport of an unstable patient all remain indications for tracheal intubation.

  
  
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  Assessment and adequate preparation of the patient prior to intubation are crucial to ensuring successful and safe intubation.

  
  
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  Awake tracheal intubation with topical anesthesia remains the preferred technique, although skilled operators can perform rapid sequence induction and intubation with a high degree of success. General anesthesia and paralysis are associated with substantial risks in critically ill, hemodynamically unstable patients.

  
  
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  The appropriate timing of tracheostomy remains poorly defined. Improved endotracheal tubes allow for prolonged intubation with a low risk of associated traumatic injury.

  
  
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  Percutaneous tracheostomy and conventional tracheostomy are increasingly performed at the bedside to minimize the hazards associated with transporting a critically ill patient to an operating room.

Tracheal intubation remains one of the most common and important procedures performed in the intensive care unit (ICU). When done well, tracheal intubation can be a lifesaving procedure. When done poorly, it may initiate a cascade of events that can lead directly or indirectly to trauma, severe complications, and death. The widespread adoption of noninvasive ventilation in the management of patients with type II acute-on-chronic respiratory failure (ACRF) and high-pressure pulmonary edema has created a population of patients who have failed moderate levels of ventilatory support and require emergent airway management (see Chap. 44). It is imperative that those who manage the airways in these patients have a high degree of knowledge, skill, and comfort in managing patients with little physiologic reserve. In addition, it is imperative that ICU physicians have knowledge and understanding of the indications for tracheal intubation, the assessment of the patient for tracheal intubation, the devices and techniques available for tracheal intubation, and the consequences and complications of tracheal intubation.¹

The decision about whether to intubate a critically ill patient requires that a practitioner at the bedside synthesize all of the information they have at their disposal about a patient, compare it to their institutional practice patterns and resources, and decide how to proceed. These decisions are rarely clear-cut; reasonable practitioners can arrive at different decisions in identical circumstances. Patients who require intubation as part of the initial management of their respiratory failure include but are not limited to those with cardiopulmonary arrest, respiratory arrest, acute respiratory distress syndrome (ARDS) of almost any cause, and any patient who is unlikely to respond to noninvasive ventilation (Table 45-1). The decision to intubate a patient after noninvasive ventilation is even more difficult to make. Triggers to convert to an invasive airway include progressive hypercapnia in spite of adequate levels of support (such as a patient with sleep apnea who is worsening on biphasic positive airway pressure [BIPAP]), unacceptably high airway pressure on noninvasive ventilation, hypoxemia that persists in spite of moderate levels of continuous positive airway pressure (CPAP) and high fraction of inspired oxygen (FiO2FiO2), diminishing mental status, patterns of respiration that suggest evolving respiratory muscle fatigue or impending respiratory arrest, and unfavorable anatomy (which is present at the start of treatment, or which evolves) (Table 45-2).

In patients with airway compromise, two decisions need to be made at the time the patient is evaluated: (1) Does this patient require an artificial airway? and (2) Does this patient require a tracheostomy? It may be difficult or impossible to translaryngeally intubate the trachea in patients with an unstable cervical spine, airway tumor, unfavorable anatomy, or significant facial trauma. Preparation for tracheostomy should occur concurrently with preparation for translaryngeal tracheal intubation in such high-risk patients.

The decision to intubate patients in cardiopulmonary arrest is a simple one, as intubation is the safest and most effective way to both ensure adequate ventilation in these patients and to protect their airway. The goal of intubating the trachea in the patient in shock is to decrease the proportion of cardiac output devoted to perfusing respiratory muscles, allowing this blood flow to be diverted to other vital organs.

All patients being evaluated for tracheal intubation should be treated with the highest FiO2 available. Oxygen saturation, blood pressure, heart rate, electrocardiography (ECG), and the frequency and strength of respiration should be closely monitored. Blood gas analysis may be helpful in facilitating the decision to intubate the patient, but has been largely supplanted by pulse oximetry, which is also essential for monitoring during intubation.

Patients requiring urgent intubation benefit from an expeditious but thorough assessment of their underlying medical conditions and airway anatomy (Tables 45-3 and 45-4). The possibility of increased intracranial pressure (ICP) or increased risk of intracranial hemorrhage is important to ascertain, since the presence of elevated ICP changes the emphasis in airway management from the maintenance of an adequate airway to the avoidance of further increases in ICP. Whereas most airway manipulation in the ICU can be done safely with patients awake, patients with elevated ICP and increased risk of intracranial hemorrhage (from unstable arteriovenous malformations or aneurysms) are best managed with intravenous general anesthesia for intubation. Laryngoscopy and tracheal intubation reliably produce myocardial ischemia in patients with coronary artery disease. Adequate anesthesia—topical and intravenous—can attenuate or prevent the myocardial ischemia associated with laryngoscopy and intubation. Inadequate anesthesia can also elicit ischemia and associated arrhythmias. Unfortunately, the use of intravenous agents in this setting is fraught with hazard. While too little intravenous agent can be associated with ischemia, too much can cause hypotension, ischemia, hypoperfusion of vital organs, and a decreased rate of redistribution of the offending agent, prolonging its cardiovascular effects. Thus, the risks and benefits of using intravenous agents must be carefully balanced and it is often best to avoid using them in these patients.

Intubation and positive pressure ventilation (PPV) will magnify the shock associated with intravascular hypovolemia. In hypovolemic patients, reflex sympathetic tone usually decreases venous capacitance, increases mean systemic pressure, and maintains venous return. Administration of sedative or anesthetic agents blunts this physiologic compensation. Following intubation, the hypoxic driven rise in sympathetic tone is removed, further decreasing peripheral vascular tone and lowering the patient’s blood pressure. PPV increases intrathoracic pressure and therefore decreases the pressure gradient driving venous return. Singly, or in combination, these effects can substantially reduce venous return, blood pressure, and tissue perfusion.² The factors that can lead to postintubation hemodynamic instability are summarized in Table 45-5. In the setting of suspected hypovolemia, intravascular volume expansion may be desirable before intubation. In any case, preparation for rapid volume infusion should be made prior to intubation.

Patients with respiratory failure require thoughtful assessment of their shunt, V/Q mismatch, and risk for bronchospasm prior to airway manipulation. The more severe their pathology, the more rapidly they will become hypoxic or hypercarbic during airway manipulation. Patients with acute hypoxemic respiratory failure are usually hypoxemic in spite of a high FiO2, and frequently desaturate further during airway manipulation. Patients with type II respiratory failure may become hypoxemic, hypercapneic, or both during airway manipulation. The more severe the lung disease, the less likely it is that ventilation with a mask or laryngeal mask airway (LMA) will be successful. Patients with severe pulmonary edema or severe bronchospasm generally cannot be ventilated successfully with a mask or LMA because the pressures and flows required to maintain an acceptable minute ventilation cannot be generated with these systems.

Manipulation of the airway in the ICU is accompanied by a substantial risk of aspiration. Unlike patients undergoing airway instrumentation in an elective setting, such as the bronchoscopy suite or operating room, patients in the ICU typically are at high risk of aspiration. Stomach contents may include enteral feedings, blood (from gastrointestinal hemorrhage), acid, and bacteria. Conditions that decrease emptying, such as diabetic gastroparesis, morbid obesity, and perhaps critical illness itself, require management as if the patient has a full stomach, even during elective airway management. For these reasons, cricoid pressure (the Sellick maneuver) should be performed whenever possible on patients undergoing tracheal intubation in the ICU.^1,3-5

The presence of a coagulopathy is a relative contraindication to nasal intubation. Techniques that are associated with a risk of bleeding, such as transtracheal injection of anesthesia, superior laryngeal nerve blocks, and retrograde intubation techniques are also relatively contraindicated when the patient is coagulopathic.

Finally, contraindications to the use of succinylcholine (see Table 45-3), the most commonly used muscle relaxant for airway management in the ICU, should be considered prior to any airway manipulation.

A variety of anatomic conditions are associated with increased difficulty of intubation by rigid laryngoscopy (see Table 45-4).⁶ A history of difficult intubation is perhaps one of the most important but least available elements of a patient’s history. The presence of many anatomic conditions makes attempts at rigid laryngoscopy and intubation in the awake or asleep patient more difficult. This in turn increases the attractiveness of techniques that allow for the patient to be awake and spontaneously breathing, and/or that do not require direct laryngoscopy, such as fiberoptic intubation, videolaryngoscopy, blind nasal intubation, and techniques that utilize an intubating laryngeal airway. Patients with severely compromised airway anatomy may be best managed by either awake fiberoptic intubation or tracheostomy. When a difficult airway is anticipated, it is best to have equipment for performing a tracheostomy immediately available, and physicians skilled at performing the procedure at hand.

In spite of the vast array of available equipment, most tracheal intubations can be accomplished using a very small subset of the equipment and a very simple checklist (Table 45-6). A cart that is fully stocked with all of the equipment required to manage a difficult airway should be available to airway managers, but need not be brought to the bedside of every patient in crisis.⁷

Ideally, bags or boxes containing the equipment on the basic list for cardiac arrest are readily available to airway managers and can be brought by them to any situation in which they may be asked to manage an airway. The more complete equipment set for urgent and elective intubation can be kept in a cart stocked specifically for this purpose. Equipment should be checked at least daily and should be stored so that it is readily accessible. It is important that the equipment is checked by the person who will use it. This procedure ensures that the airway manager can focus on the patient during airway manipulation, and is not distracted by equipment failures, equipment checks, or preparation.

PHARMACOLOGIC PREPARATION AND USE

The goals of pharmacologic preparation of the patient include creating conditions that allow safe intubation, providing relief from the discomfort and hemodynamic consequences associated with airway manipulation and tracheal intubation, and decreasing the hormonal and neurologic consequences of the procedure. The spectrum of pharmacologic preparation ranges from topical anesthesia to intravenous general anesthesia. In the hands of experienced operators, most airway manipulations can be accomplished with topical anesthesia alone. Intravenous general anesthesia is indicated in the setting of elevated ICP and favorable airway anatomy (Table 45-7). There are many institutions where an intravenous general anesthetic is routinely administered for all emergency tracheal intubations, but this practice is not without significant risks. The majority of the literature suggests that the use of intravenous general anesthesia to facilitate airway management may be associated with a higher rate of failure and need for emergency tracheostomy/cricothyroidotomy, especially in less experienced hands. So the risks of giving a general anesthetic based on the patient’s airway anatomy and physical status and the experience of the airway manager must be weighed against the advantages of potentially improved airway visualization prior to proceeding with a general anesthetic.

Patients who require urgent intubation benefit from pharmacologic preparation when circumstances allow. The administration of 0.2 mg IV glycopyrrolate will dry the mouth and facilitate direct laryngoscopy or fiberoptic laryngoscopy. The oropharynx can be anesthetized topically with 4% lidocaine spray, followed by approximately 1 to 2 mL of 2% to 5% lidocaine jelly or ointment on an oral airway of appropriate size for the patient. The central channel of the oral airway can also be used to direct topical anesthetic at the vocal cords. The use of lidocaine for topical anesthesia is preferable to benzocaine, as the latter can cause methemoglobinemia. Care should be taken to avoid giving high doses (>6 mg/kg) of lidocaine for topical anesthesia, since lidocaine is readily absorbed by the mucosa of the pharynx and symptoms of local anesthesia toxicity can develop above this dose. Some practitioners routinely perform transtracheal or superior laryngeal nerve blocks to facilitate awake intubation, but these procedures add little to topical anesthesia of the proximal airway, and can cause significant bleeding in coagulopathic patients. In addition, topical/local anesthesia schemes that avoid anesthetizing the trachea have several advantages in the ICU setting. They allow the patient to retain some ability to protect from aspiration, and they also allow confirmation of tracheal intubation when the patient coughs in response to introduction of the tube into the trachea.

The use of intravenous agents to facilitate tracheal intubation in the ICU can be hazardous. The degree of hypovolemia, myocardial dysfunction, and shock that often exists in these patients is difficult to ascertain prior to manipulating the airway in an urgent situation. Doses of intravenous agents that are well tolerated or even subtherapeutic in healthy patients can precipitate respiratory arrest or circulatory collapse in critically ill patients, converting a serious situation into a desperate one. Intravenous lidocaine in a dose of 100 mg is frequently sufficient to induce general anesthesia in patients with shock. The use of intravenous agents such as midazolam, fentanyl, thiopental, etomidate, propofol, and ketamine should be restricted to experienced practitioners. When indicated, these agents may be used to either titrate up to an acceptable level of sedation (which will be accompanied by a corresponding decline in both hemodynamics and minute ventilation, with associated worsening of hypoxia and hypercapnia), or to deliberately induce a brief period of general anesthesia.

MUSCLE RELAXANTS AND AIRWAY MANAGEMENT IN THE INTENSIVE CARE UNIT

The use of muscle relaxants to facilitate airway management in the ICU remains controversial. Although these agents are routinely administered to facilitate airway management in the operating room, their use in ICU patients is probably not essential. The use of intravenous induction agents to initiate general anesthesia is motivated by the desire to produce intubating conditions quickly and to minimize unpleasant recall. Most patients undergoing elective surgery tolerate the hemodynamic consequences of intravenous anesthetic agents well and can be readily oxygenated and ventilated with a bag and mask. When anesthesiologists are confronted with patients who have abnormal airway anatomy or who may be impossible to oxygenate or ventilate with a bag and mask, they typically opt for awake intubation strategies, as outlined in this chapter. Muscle relaxants, including succinylcholine, vecuronium, mivacurium, rocuronium, and cisatracurium should be used only by those who are experienced in managing the airway with an Ambu bag and mask, and who are thoroughly versed in techniques used to manage the difficult airway. The reason for this stipulation is that once these agents are administered, it is imperative that a definitive airway is obtained within minutes. Attempts at ventilating most patients in respiratory failure with an Ambu bag and mask are often difficult and frequently futile, since the decreased compliance of the lungs and/or increased airway resistance makes it difficult to maintain adequate minute ventilation. This is especially likely to be an issue when a “rapid sequence” intubation is planned for a patient in whom there are concerns about aspiration since with this technique there is no effort to ensure that bag-mask ventilation will be possible prior to administering the muscle relaxant. Among muscle relaxants available to facilitate airway management, succinylcholine remains the agent of first choice in ICU and ER patients for whom it is not contraindicated.⁸

There is an established literature supporting the use of intravenous anesthetic agents and muscle relaxants to facilitate airway management in both the field and the emergency department.^9-19 This literature suggests that the use of intravenous agents can both improve intubating conditions and cause hypotension, and that brain-injured trauma patients have worse outcomes.^20,21 Airway management utilizing muscle relaxants in these reports is associated with a success rate in the range of 94% to 99%, with 1% of patients requiring a surgical airway of some kind. At first glance, this appears to be conspicuous success, but compared to airway management in the operating room, it is a very high rate of failure, and a very high rate of requirement for a surgical airway. No doubt some of the need for surgical airways in these patients is a consequence of their pathology, their anatomy, and the circumstances surrounding their airway management. Nevertheless, it seems plausible if not certain that the requirement for a surgical airway in some of these patients is a consequence of the use of either intravenous anesthetics or muscle relaxants as part of their airway management.