Preoxygenation--the importance of a good face mask seal.

We have studied 16 healthy volunteers whose lungs were preoxygenated six times each in order to assess the amount of room air entrained during tidal volume preoxygenation if a good seal is not maintained between the face mask and the face. With a fresh gas flow of 10 litre min-1, we found that using gravity alone to hold the face mask in position, more than 20% room air was entrained; if the face mask was held adjacent to the face, more than 40% room air was entrained.