Preoxygenation: a comparison of three different breathing systems

An end-tidal expiratory oxygen concentration (FE'O2) greater than 0.90 is considered to be adequate for preoxygenation. This is generally achieved using a face mask, but this can be unsatisfactory in some patients. We compared preoxygenation in 30 healthy volunteers using a face mask, the NasOral system, which is a novel preoxygenation device, and a mouthpiece with a nose-clip. We measured the maximal FE'O2, the FE'O2 after 2 min and the time to reach maximal FE'O2 and recorded the subjective judgement of the volunteers. The maximal FE'O2 with face mask and mouthpiece was significantly greater than with the modified NasOral system (P<0.05 and P<0.01). With the former devices, a FE'O2 of 0.90 was achieved in 73% of the volunteers vs 46% with the modified NasOral system. Using the mouthpiece, the FE'O2 after 2 min was significantly higher than using the face mask (P<0.01) or the modified NasOral system (P<0.01). The time to maximal FE'O2 was significantly shorter using the modified NasOral system than with the face mask or mouthpiece (P<0.001 and P=0.0001). The volunteers gave more positive ratings to the face mask and mouthpiece than to the modified NasOral system (P<0.001 and P<0.01). We conclude that the use of a mouthpiece can improve preoxygenation in some patients. The results obtained with the modified NasOral system do not justify its introduction into clinical practice.