As a discipline, anesthesiology has served to meaningfully advance patient safety. In this context, airway management in dedicated procedural settings has benefited from algorithmic guidance, novel pharmaceuticals, and technological advancements. Out of the OR, however, myriad physiologic and contextual factors conspire to complicate airway management. Such intubations are often emergent, performed in patients who are unstable, and require the clinician to work in suboptimal conditions with little time to prepare or examine the patient (West J Emerg Med 2015;16:1109-17).
Physiologically difficult airway management: Incidence, risk factors, and outcomes
A recent international prospective observational study (INTUBE) of 2,964 critically ill adults undergoing intubation in the ICU demonstrated that physiologic difficulty associated with airway management is more common than technical, or anatomic, difficulty (JAMA 2021;325:1164-72). Peri-intubation cardiovascular instability accompanied 42.6% of all intubations, followed by severe hypoxemia in 9.3%, and cardiac arrest in 3.1%. Meanwhile, only 4.5% of intubations required more than two attempts, and only five patients could not be intubated. These findings underscore the continued importance of technical airway management fundamentals and the importance of approaches to mitigate peri-intubation physiologic derangements.
Physiologic and personnel factors (e.g., SpO2 <80%), and not just anatomic features (e.g., Mallampati score), have been associated with technically difficult airway management in the ICU (Am J Respir Crit Care Med 2013;187:832-9). Technically difficult and therefore prolonged intubation attempts are associated with adverse physiologic and clinical outcomes. Additionally, baseline hypoxemia and hypotension, among other physiologic variables, have been associated with peri-intubation cardiovascular instability and/or cardiac arrest in critically ill adults (Crit Care Med 2018;46:532-9; PLoS One 2020;15:e0233852). In INTUBE, mortality was 40.7% among those who experienced a major adverse peri-intubation event versus 26.3% among those who did not (absolute risk difference, 14.4%; 95% CI, 10.9%-17.9%; P < 0.001). It follows then that approaches to optimize preoxygenation, enhance the odds of first-pass success, and manage hemodynamic instability are important areas of focus.
Optimizing preoxygenation
Successful preoxygenation minimizes the adverse effects of hypoxemia during apnea, including dysrhythmias, cardiovascular instability or collapse, and hypoxic brain injury (Ann Emerg Med 2012;59:165-75; Am J Emerg Med 2017;35:1177-83; N Engl J Med 2019;380:811-21). The 2022 ASA Practice Guidelines for Management of the Difficult Airway accordingly highlight both preoxygenation and the delivery of supplemental oxygen during airway management when feasible (Anesthesiology 2022;136:31-81). However, many critically ill adults requiring definitive airway management have hypoxemic respiratory failure with underlying derangements in gas exchange that serve to limit the efficacy of traditional preoxygenation approaches (Crit Care Med 2009;37:68-71).
Oftentimes, positive pressure is required to overcome airway collapse in patients with shunt physiology. Both noninvasive positive pressure ventilation (NIPPV) and heated high-flow nasal oxygen (HHFNO) have been associated with improved oxygenation during intubation attempts in high-risk critically ill adults compared to conventional oxygen therapy (Crit Care 2019;23:319). Nasal oxygen administration has the additional benefit of continuing oxygen delivery during airway management, thereby facilitating some degree of apneic oxygenation, and can be used in conjunction with other techniques (West J Emerg Med 2018;19:403-11). In patients where adequate seal with a full facemask is difficult, nasal masks can achieve improved fit and more effective ventilation, suggesting that nasal pressurization may relieve upper-airway obstruction by displacing the soft palate and tongue forward and away from the posterior pharyngeal wall (J Anaesthesiol Clin Pharmacol 2016;32:314-18; Crit Care 2013;17:R300). Adequate oxygenation prior to, and during airway management extends safe apnea time, improves patient outcomes, and is recommended whenever possible.
Achieving first-pass success
Multiple intubation attempts are associated with adverse events and worsened patient outcomes. This may be due to airway trauma with prolonged laryngoscopy, progressive hypoxemia, esophageal intubation or aspiration, adverse hemodynamic conditions, and/or the need for sedatives or neuromuscular-blocking agents (NMBAs) (Ann Emerg Med 2012;60:749-54.e2). Intubation-related complications increase with each attempt, and more than one attempt has been associated with a fourfold increase in severe complications and fivefold increase in total complications (Anesth Analg 2015;121:1389-93; J Clin Anesth 2014;26:167). In certain patient populations, such as those with traumatic brain injury, cardiovascular disease, or septic shock, hypoxemia associated with multiple intubation attempts may be devastating, and first-pass success is paramount.
Key elements to enhancing first-pass success include appropriate clinician training and experience, preparation and management of the environment, proper patient positioning, appropriate equipment availability, and backup planning (Can J Anaesth 2017;64:530-39). Additionally, NMBAs improve the odds of first-pass intubation success in critically ill adults, even when using videolaryngoscopy (Ann Am Thorac Soc 2015;12:734-41). With respect to the laryngoscopy approach, systematic review and meta-analysis suggest that all categories of videolaryngoscopy are associated with increased odds of first-pass success compared to direct laryngoscopy and that hyperangulated designs perform best (Br J Anaesth 2022;129:612-23). In a systematic review examining out-of-OR intubations, videolaryngoscopy was associated with increased first-pass success and decreased odds of esophageal intubation in critically ill adults compared to direct laryngoscopy, which was also demonstrated in less experienced providers (Br J Anaesth 2018;120:712-24).
Mitigating hemodynamic trespass
Airway management performed in nonoperating room settings is associated with an increased risk of complications, with the most frequent being peri-intubation cardiovascular instability (37-43%) (Br J Anaesth 2016;117 Suppl 1:i5-i9; PLoS One 2020;15:e0233852; JAMA 2021;325:1164-72). Not only is peri-intubation cardiovascular instability common, it is also associated with poor outcomes in nonoperating room patients (Crit Care 2020;24:682; J Intensive Care Med 2022;37:1467-79). Therefore, identifying risk factors for this complication is vital to the success of airway management in nonoperating room patients, including the critically ill. Based on available evidence thus far, one can synthesize an approach to mitigating peri-intubation cardiovascular collapse during airway management in nonoperating room patients, as described below:
First, evaluate patient characteristics that are associated with peri-intubation hemodynamic instability: older age, high illness severity score, history of heart failure, or hematologic malignancy. Second, evaluate pre-intubation characteristics associated with an elevated risk: diuretic or fluid bolus administration in the 24 hours preceding intubation; push dose pressor administration or continuous vasoactive infusion pre-intubation; or MAP <65 mmHg, SBP <90 mmHg, or shock index >0.9. Third, evaluate procedural characteristics associated with an elevated risk; for example, intubation in the setting of cardiogenic shock or hemodynamic collapse. Fourth, consider calculating the Hypotension Prediction Score (PLoS One 2020;15:e0233852).
If the above assessment indicates a heightened risk, consider modifying the airway management technique to include a fluid bolus and/or bolus dose vasopressors pre-intubation while ensuring appropriate personnel and equipment are available to achieve first-past success. Additionally, the choice of sedative hypnotic is likely to impact hemodynamic outcomes, and ketamine, a ketamine/propofol admixture, etomidate, or nothing may yield the most favorable hemodynamic outcomes (Am J Respir Crit Care Med 2022;206:449-58; J Trauma Acute Care Surg 2019;87:883-91; Intensive Care Med 2022;48:78-91; Lancet 2009;374:293-300).
When approaching airway management in critically ill adults outside the OR, evaluation of both anatomic and physiologic considerations that may impact outcomes must be undertaken in concert. Recognizing that cardiovascular instability and hypoxemia are the two most common adverse events associated with airway management in this patient population, their mitigation is a natural area of focus. Additionally, prolonged airway management confers substantial risks, and efforts should be made to optimize first-pass success.