BACKGROUND: At sea level, performing chest compressions is a demanding physical exercise. On a commercial flight at cruise altitude, the barometric pressure in the cabin is approximately equal to an altitude of 2438 m. This results in a Po₂ equivalent to breathing an FIo₂ of 15% at sea level, a condition under which both the duration and quality of cardiopulmonary resuscitation (CPR) may deteriorate. We hypothesized that rescuers will be able to perform fewer rounds of high-quality CPR at an FIo₂ of 15%.METHODS: In this crossover simulation trial, 16 healthy volunteers participated in 2 separate sessions and performed up to 14 2-min rounds of chest compressions at an FIo₂ of either 0.15 or 0.21 in randomized order. Subjects were stopped if their Spo₂ was below 80%, if chest compression rate or depth was not achieved for 2/3 of compressions, or if they felt fatigued or dyspneic.RESULTS: Fewer rounds of chest compressions were successfully completed in the hypoxic than in the normoxic condition, (median [IQR] 4.5 [3,8.5]) vs. 5 [4,14]). The decline in arterial Spo₂ while performing chest compressions was greater in the hypoxic condition than in the normoxic condition [mean (SD), 6.19% (4.1) vs. 2% (1.66)].DISCUSSION: Our findings suggest that the ability of rescuers to perform chest compressions in a commercial airline cabin at cruising altitude may be limited due to hypoxia. One possible solution is supplemental oxygen for rescuers who perform chest compressions for in-flight cardiac arrest.Clebone A, Reis K, Tung A, OConnor M, Ruskin KJ. Chest compression duration may be improved when rescuers breathe supplemental oxygen. Aerosp Med Hum Perform. 2020; 91(12):918922.