The use of high-flow nasal oxygen

In the last decade, the use of high-flow nasal oxygen (HFNO), a technique of noninvasive respiratory support, has become widespread in critically ill patients. With HFNO, up to 60 L/min of fresh gas flow generated by an air/oxygen blender or a turbine is conditioned by a heated humidifier (temperature 31–37°C, absolute humidity 30–44 mgH2O/L) and administered to the patient through large-bore nasal cannulas. HFNO has several beneficial physiological effects including the accurate delivery of the set FiO2, the washout of anatomical deadspace and the reduction of breathing effort, the increase in positive airway pressure with improvement in lung aeration, in oxygenation and in respiratory mechanics, and the optimization in patients’ comfort (Fig. 1) [1]. As many of the effects of HFNO are flow-dependent, maximum tolerated flows should be delivered to maximize the respiratory support, while temperature should be set according to patient’s comfort and FiO2 should be tailored on the target SpO2. More recently, HFNO delivered through asymmetric nasal cannulas has been proposed with the aim of further enhancing carbon dioxide washout and increasing the airway pressure generation. The physiological effects of this design are currently under investigation. We hereby summarize the most recent evidence regarding HFNO use in the intensive care unit.