Reliability of methods to estimate the fraction of inspired oxygen in patients with acute respiratory failure breathing through non-rebreather reservoir bag oxygen mask.

Abstract

Severity of hypoxaemia can be assessed using the partial pressure of arterial oxygen to fraction of inspired oxygen ratio (FiO₂). However, in patients breathing through non-rebreather reservoir bag oxygen mask, accuracy of bedside FiO₂ estimation methods remains to be tested. In a post-hoc analysis of a multicentre clinical trial, three FiO₂ estimation methods were compared with FiO₂ measured with a portable oxygen analyser introduced in the oxygen mask. Among 262 patients analysed, mean (SD) measured FiO₂ was 65% (13). The 3%-formula (21% + oxygen flow rate in L/min × 3) was the most accurate method to estimate FiO₂ Other methods overestimated FiO₂ and hypoxaemia severity, so they should be avoided.