Methods.Forty-eight adult patients were randomly assigned to one of eight groups according to the anesthetic machine, fresh gas flow (FGF), and the use of HME (n = 6 each): Cato 0.5l·min^–1 without HME (group 1), Cato 1.0l·min^–1 without HME (group 2), Cato 0.5l·min^–1 with HME (group 3), Cato 1.0l·min^–1 with HME (group 4), Aestiva 0.5l·min^–1 without HME (group 5), Aestiva 1.0l·min^–1 without HME (group 6), Aestiva 0.5l·min^–1 with HME (group 7), and Aestiva 1.0l·min^–1 with HME (group 8). The temperature and AH of the anesthetic gases were measured with a Moiscope (S.K.I. Net, Tokyo, Japan), which was placed between the endotracheal tube and the Y-piece of the anesthetic circuit. The HME was placed between the Moiscope and the Y-piece of the anesthetic circuit. The temperature and AH of the anesthetic gases were measured at 5, 10, and 15min and then every 15min up to 150min after tracheal intubation.

Results.Among the groups without HME (groups 1, 2, 5, and 6), the inspired temperatures and AH in groups 1 and 2 were significantly higher than those in groups 5 and 6 at all times during the study period (P 0.01–0.001). The inspired temperatures and AH of the groups with HME (groups 3, 4, 7, and 8), were significantly higher than those in groups 2, 5, and 6 (P 0.01–0.001). Among the groups with HME, the AH in group 3 was significantly higher than that in group 8 until the final study period.

Conclusion.The present study indicates that the DrÄger Cato machine was more effective in warming and humidifying respiratory gas than the Aestiva/5, and that Aestiva/5 without HME does not reach the optimal temperature and humidity ranges, even if minimal flow anesthesia (0.5l·min^–1) is performed.