Tracheal intubation

Introduction

Tracheal intubation is a commonly performed, high-risk procedure in critically ill patients. There are important differences between elective intubation in the operating room compared with emergency intubation in the intensive care unit (ICU). Risks associated with emergent intubation in the critically ill include hypoxemia, hemodynamic instability, cardiac arrest, and death, underlining the importance of a systematic approach to optimize physiologic conditions and maximize first-attempt success. Although a wide variety of advanced airway devices are now available to help overcome anatomic difficulties and deliver rescue oxygenation, the best evidence-based approach for utilizing these tools in the ICU patient remains poorly defined. The goal of this chapter is to provide a systematic approach using best evidence to maximize the success and safety of tracheal intubation in the ICU.

Patient factors and airway assessment

Reported complication rates from tracheal intubation in the critically ill range from 4.2% to 22% and remain unacceptably high in comparison with operating room procedures. The Fourth National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society (NAP4) reported that 25% of adverse airway events occurred in the ICU and emergency department (ED). Inadequate identification of high-risk patients combined with poor planning, inadequate preparation, and ineffective teamwork were the primary causal and contributing factors to these adverse events.

Physiologic assessment

Decompensated cardiopulmonary disease and shunt physiology make preoxygenation more difficult in the critically ill, shortening the safe apnea time during intubation before hypoxemia develops. Hemodynamic instability is an independent predictor of death after intubation, underscoring the importance of an individualized approach to high-risk patients, including those with severe valvular disease, pulmonary hypertension, right ventricular failure, and high shock index. The combination of desaturation and hypotension increases the likelihood of cardiac arrest.

Anatomic assessment

Emergent airway management leaves little time to perform a thorough airway assessment and less time to plan the approach when high-risk features are present. In conscious and cooperative patients, an inability to bite the upper lip with the lower incisors may be the single best predictor of difficult laryngoscopy. Other features predict difficult laryngoscopy. These include those that limit the ability to open the airway (interincisor distance, large tongue), displace the tongue into the submental space (large tongue, short mandible, short thyromental and hyomental distances), and/or impair alignment of the visual axes (cervical mobility). Features that predict difficult bag-valve-mask ventilation (BMV) include obesity, facial hair, advanced age, history of sleep apnea, and being edentulous. Features that predict difficult supraglottic device use include restricted mouth opening, a distorted airway, reduced lung compliance, and upper airway obstruction.

Common methods of airway assessment are limited in their ability to correctly identify patients with a difficult airway (positive predictive value, 4%–27%). ^, The MACOCHA score, a seven-item prediction scale for the critically ill, is the only validated tool for identifying high-risk patients. ^,

Optimizing airway management in the critically ill

Positioning

Optimal patient positioning is important to maximize the success of both preoxygenation and laryngoscopy attempts. Upright positioning can optimize functional residual capacity (FRC), especially in obese and pregnant patients, which combined with careful preoxygenation, can prolong the safe apnea time during intubation. A recent randomized trial showed increased difficulty with direct laryngoscopy using the “ramped” position (head of bed elevated 25 degrees, face parallel to the floor) compared with the “sniffing” position (supine, neck flexed, head extended). Combining ramped with sniffing positions may improve first-pass intubation success, especially in obese patients.

Preoxygenation and apneic oxygenation

Critically ill patients run higher risks of life-threatening hypoxemia. Preoxygenation is generally limited by the size of the FRC and the ability to denitrogenate this space. In the critically ill, the degree of physiologic shunting is a major limiting factor to preoxygenation. Rapid-sequence intubation has an inherent delay of 45–90 seconds between medication administration and laryngoscopy. A recent multicenter trial demonstrated that mask ventilation during the apneic period after induction reduced the incidence of severe hypoxemia without increased aspiration risk. Noninvasive positive pressure ventilation (NIV) and high-flow nasal cannula (HFNC) have been shown to improve preoxygenation. A randomized trial failed to demonstrate clear benefit with routine apneic oxygenation in the critically ill, and this practice remains controversial. In patients with refractory hypoxemia there is no safe apnea time, and awake intubation should be strongly considered when oxygenation can be assured during the procedure.

Rescue oxygenation

Avoiding hypoxemia is essential to preserve safe patient conditions during intubation. If oxygen saturations drop significantly during this procedure, the first rescue maneuver is the two-person BMV technique using an oropharyngeal airway and meticulous attention to patient positioning. If this maneuver proves inadequate, a second-generation supraglottic airway should be used expediently. ^, ^, Airway managers must also be prepared to perform an emergent cricothyrotomy when a definitive airway cannot be secured and life-threatening hypoxemia persists after such maneuvers.

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