Physiologically Difficult Airways in Emergency Medicine: A Narrative Review of Recognition, Resuscitation, and Management Strategies

The focus of managing critically ill patients' airways has traditionally centered around anatomically complicated issues, however an increasing amount of literature indicates that peri-intubation complications are likely to be related to the patient's physiologic state at the time of intubation. Physiologic instability may lead to severe hypoxemia, cardiovascular collapse, or cardiac arrest even when the anatomy of the airway is uncomplicated. Shock states, severe metabolic acidosis, right heart failure, or an insufficient oxygen reserve may contribute to these unstable conditions but they often remain undetected. The lack of inclusion of physiological instability as part of many modern predictive models, guidelines, and algorithms also contributes to the lack of a standard framework or standardized thresholds for using physiological data (oxygenation indices, hemodynamic profiles, acid-base status, bedside cardiac assessment) to determine optimal timing or techniques of airway management. The current paper reviews the available literature to identify the best methods for identifying and managing patients who have a physiologically difficult airway. These include performing an integrated assessment of the patient's physiology, optimizing both gas exchange and perfusion before inducing anesthesia, choosing induction strategies that will result in the least harm to the cardiovascular system, using multiple modalities of prediction instruments to assess the likelihood of developing physiological instability during airway management, utilizing point-of-care ultrasound, and employing awake or modified rapid sequence intubation techniques appropriately. A "physiology first" approach provides a model to decrease the incidence of hypoxemia and circulatory collapse during the process of airway management. To further develop and advance the field of emergency and critical care medicine, it is recommended to standardize the pre-intubation physiologic screen, incorporate proven physiologic markers into existing airway algorithms, and support the development of future research studies aimed at establishing standardized thresholds, improving existing prediction models, and providing guidance on pre-intubation optimization of critically ill and emergently ill patients in emergency and critical care.