Four Methods of Pre-oxygenation

After 3 minutes of oxygen supplementation (preoxygenation), with each of the devices listed below, the exhaled oxygen content will be measured. All participants were enrolled in a single arm in which they underwent 4 interventions in series: 1) Simple mask at 60 L/min for 3 minutes 2) Non-rebreather at 60 L/min for 3 min 3) Non-rebreather at 15 L/min for 3 minutes 4) Bag valve mask at 15 L/min for 3 minutes