The Physiologically Difficult Airway

The physiologically difficult airway is defined as one in which severe physiologic derangements place patients at increased risk of cardiovascular collapse and death during tracheal intubation and transition to positive pressure ventilation. Patients with a physiologically difficult airway can be divided into those who are critically ill and those who are not. The critically ill patient with a physiologically difficult airway may present with hypoxaemia, hypotension, right ventricular failure, metabolic acidosis and neurologic injury. Noncritically ill patients with a physiologically difficult airway are patients who are obese, paediatric, pregnant or at risk of aspiration during tracheal intubation (after a meal, with gastroesophageal reflux disease, intestinal obstruction, etc ). Recognition of this high-risk group of patients is essential to implement measures to avoid complications during tracheal intubation. Unlike the anatomically difficult airway, where placing the endotracheal tube safely within the trachea is the primary goal, in patients with a physiologically difficult airway, prevention of adverse events is equally important during airway management. Strategies to prevent complications associated with physiologically difficult airway include measures to improve the chance of first-pass success, effective peri-intubation oxygenation and measures to avoid hypotension and haemodynamic collapse.