High-flow nasal oxygen therapy in intensive care and anaesthesia.

Oxygen therapy is first-line treatment for hypoxaemic acute respiratory failure (ARF). High-flow nasal oxygen therapy (HFNO) represents an alternative to conventional oxygen therapy. HFNO provides humidified, titrated oxygen therapy matching or even exceeding the patients' inspiratory demand. The application of HFNO is becoming widespread in Intensive Care Units (ICUs), favoured by increasing evidence based on numerous studies supporting its efficacy. The mechanisms of action and physiological effects of HFNO are not yet fully understood. Pharyngeal dead space washout, decrease in airway resistance, generation of a positive end-expiratory pressure, and enhanced delivery of oxygen are all alleged to be potential mechanisms. The emerging evidence suggests that HFNO is effective in improving oxygenation in most patients with hypoxaemic ARF of different aetiologies. Notwithstanding the potential benefit of HFNO in the management of hypoxaemia, further large cohort studies are necessary to clarify the indications, contraindications and factors associated with HFNO failure. HFNO may also be valuable in reducing the need for tracheal intubation in the management of post-extubation ARF. In addition, HFNO has been proposed to limit oxygen desaturation by prolonging apnoeic oxygenation during intubation both in ICUs and operating theatres.