Preoxygenation: a study of denitrogenation.

Controversy exists as to the most appropriate method for preoxygenation of patients prior to induction of anesthesia (1-5). The recommendations for adequate preoxygenation have varied from normal breathing of 100% oxygen for periods of 10 minutes (2) to taking four maximal breaths over 30 seconds (6). Most studies have measured oxygen saturation or content of blood rather than the actual content of nitrogen in the lungs (1-15). It is the wash out of nitrogen from the lungs that is the key to achieving adequate preoxygenation. Recently, the four maximal breath technique of preoxygenation was found to be associated with a statistically significant shorter time to onset of oxygen desaturation of blood when compared with normal breathing of 100% oxygen for 3 minutes (8). These results suggest that the four breath technique of preoxygenation, although fully saturating hemoglobin, does not provide as complete a denitrogenation of the lungs as does 3 minutes of normal breathing of 100% oxygen. To try to determine the basis for this difference, we used mass spectrometry to compare the effectiveness of nitrogen washout from the lungs under three different preoxygenation regimens: 1) normal tidal breathing of 100% 0, until end-tidal N, was <1%; 2) maximal breathing of 100% 0, to total lung capacity; and 3) taking eight vital capacity breaths of 100% 0,.

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