Comparison of four methods of preoxygenation.

We studied four different techniques of preoxygenation in 20 healthy volunteers, by continuous analysis of respired gases. Three minutes of tidal breathing from a Magill breathing system or four vital capacity breaths from a non-rebreathing system were found to be equally effective, whereas four vital capacity breaths from a Magill breathing system were less effective. Maximal expiration before application of the face mask resulted in improved oxygenation when four vital capacity breaths were taken from a Magill system.