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.
- critical care
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Contributors All authors designed the study, wrote the manuscript together and approved the final version of the manuscript. All authors give their agreement to be accountable for all aspects of the work, and ensure the accuracy and integrity of any part of the work.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests RC reported receiving grants from the French Ministry of Health, Le Nouveau Souffle, AADAIRC, French Intensive Care Society and European Respiratory Society, and non-financial support from Fisher & Paykel Healthcare and MSD outside the submitted work. J-PF reported receiving grants from the French Ministry of Health and personal fees and non-financial support from Fisher & Paykel Healthcare outside the submitted work. CG reported non-financial support, personal fees and logistic support from Fisher & Paykel, Resmed and Lowenstein Medical. AWT reported receiving grants from the French Ministry of Health, personal fees and non-financial support from Fisher & Paykel Healthcare, and personal fees from Maquet-Getinge, GE Healthcare and Covidien outside the submitted work.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
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