• Critical Care
• Respiratory Infection

High-flow nasal oxygen (HFNO) is widely used in intensive care units (ICUs) and now being considered as a first-line oxygenation strategy for management of patients with acute hypoxaemic respiratory failure.1 Benefits of HFNO can be explained by its physiological effects including high FiO₂ delivery, low levels of positive pressure in the upper airways and ventilatory support due to dead-space wash-out, leading to decreased respiratory rate and work of breathing.2 The FLORALI trial was the seminal study, showing clinical benefits of HFNO as compared with conventional oxygen therapy (COT) or non-invasive ventilation (NIV) in patients with acute hypoxaemic respiratory failure, that is, hypoxaemia and respiratory rate above 25 breaths/minute.3 Whereas the risk of mortality was significantly lower with HFNO as compared with COT or NIV, the risk of intubation decreased only in patients with moderate-to-severe hypoxaemia (ratio of partial pressure of arterial oxygen to fraction of inspired oxygen, PaO₂/FiO₂<200 mm Hg), ranging from 35% to 50%, a finding suggesting that beneficial effects are more pronounced in patients with greater respiratory severity. Consequently, clinical practice guidelines drawn up before COVID-19 pandemic suggested the use of HFNO over COT or NIV in patients with acute hypoxaemic respiratory failure, although it was only a conditional recommendation.1

In patients with COVID-19-related respiratory failure admitted in ICUs, two large-scale clinical …