Difference in PaO 2 /FiO 2 between high-flow nasal cannula and Venturi mask in hypoxemic COVID-19 patients

The ratio between arterial blood partial pressure of oxygen and fraction of inspired oxygen (PaO 2 /FiO 2 ) was largely used for grading and managing the respiratory failure in non-mechanically ventilated COVID-19. In these patients, the assessment of the true FiO 2 in the inspired mixture may be difficult with consequent inaccuracies in PaO 2 /FiO 2 assessment. In 30 severe COVID-19 patients, we observed that PaO 2 /FiO 2 values measured immediately before and after the transition from high-flow nasal cannula (HFNC) to one commercially available Venturi mask O 2 therapy were similar (bias mean value 0, standard deviation 23 mmHg). In COVID-19 patients recovering from respiratory failure, PaO 2 /FiO 2 is not different whether measured with a commercially available Venturi mask or HFNC.