Preoxygenation via a non-rebreather mask comparing a standard oxygen flowmeter rate of 15 Lpm to maximally open.

Dear Editor, Preoxygenation is critical to safe emergency airway management with an end-tidal oxygen (ETO2) of >90% considered the target prior to induction. Outside of the operating theatre and in prehospital environments, turning open the valve of a standard wall/cylinder outlet past the 15 Lpm graduation (‘overflow’) has been proposed to greatly enhance preoxygenation via a non-rebreather mask (NRB), achieving an ETO2 of 86% in a recently published report. However, this study used an American 15 L/min flowmeter that allows oxygen flow of 40–60 Lpm if opened fully, while previous work with NRB masks with standard oxygen flow rates of 15 Lpm produce an ETO2 of only 50–65% and standard Australian oxygen outlets may only increase this flow to 19 Lpm when completely open. Therefore, preoxygenation may not be improved by such a margin for all types of 15 Lpm flowmeters.