High-Flow Nasal Oxygen in Contemporary Airway Management: Enhancing Physiological Safety in Anaesthesia-A Narrative...

High-flow nasal oxygen (HFNO) has become an increasingly important component of contemporary airway management, extending beyond its origins as a therapy for hypoxaemic respiratory failure to a versatile perioperative tool used across operating theatres, non-operating-room anaesthesia (NORA), and critical care settings. By delivering heated, humidified oxygen at high flow rates, HFNO provides a range of physiological benefits including reliable oxygen delivery, anatomical dead-space washout, low-level positive airway pressure, and facilitation of apnoeic oxygenation. This narrative review explores the physiological mechanisms underpinning HFNO and examines its evolving role in modern anaesthetic practice. The evidence supporting its use for preoxygenation, apnoeic oxygenation, postoperative respiratory support, procedural sedation, tubeless airway surgery, and management of the physiologically difficult airway is reviewed. Particular attention is given to high-risk populations, including patients living with obesity, obstetric patients, and children, as well as applications in a range of NORA environments. The review also examines key limitations and safety considerations, including hypercapnia, aspiration risk, airway obstruction, airway-fire hazards, human factors, and emerging concerns regarding environmental sustainability. While HFNO can improve oxygenation and increase the margin of safety during periods of physiological vulnerability, it should not be viewed as a substitute for definitive airway management or vigilant monitoring. HFNO represents a significant advance in physiology-centred airway management. Its greatest value lies not in routine application, but in thoughtful integration into broader airway safety strategies where meaningful physiological or patient-centred benefit is anticipated.