COMPARISON OF SUPRAGLOTTIC AIRWAY VERSUS FACE MASK VENTILATION PRIOR TO TRACHEAL INTUBATION: IMPACT ON OXYGENATION AND AIRWAY CONTROL

Abstract

Preoxygenation and the maintenance of adequate ventilation before tracheal intubation are foundational steps in the safe conduct of general anaesthesia1-2. The physiological rationale underlying preoxygenation is straightforward: room air breathing leaves the functional residual capacity (FRC) composed predominantly of nitrogen, with only a modest oxygen reservoir of approximately 450 mL. When a patient breathes 100% oxygen for an adequate period, nitrogen within the FRC is progressively washed out and replaced with oxygen, expanding the reservoir to nearly 3000 mL in a healthy adult. This “denitrogenation” markedly prolongs the duration of safe apnoea – the interval between the onset of apnoea following induction and neuromuscular blockade, and the point at which arterial oxygen saturation begins to fall to unsafe levels. Because induction of anaesthesia is almost invariably followed by a period without spontaneous ventilation, whether due to drug-induced apnoea, loss of airway tone, or the time required to achieve a laryngoscopic view, the size of this oxygen reserve determines the safety margin available to the anaesthesiologist before hypoxaemia supervenes. Failure of oxygenation and ventilation during this critical window remains one of the most consistently reported preventable causes of anaesthesia-related morbidity and mortality, as highlighted by the Fourth National Audit Project of the Royal College of Anaesthetists and the Difficult Airway Society, which identified airway and ventilation-related events as major contributors to catastrophic outcomes during general anaesthesia.1