• K W Fritz, A Osterhaus, and J Mottner.
• Abteilung I des Zentrums für Anästhesiologie, Medizinische Hochschule Hannover.
• Anaesthesiol Reanim. 1992 Jan 1; 17 (3): 133-44.

AbstractThis study looks at the question of whether anaesthetic gases are sufficiently moistened in a semi-closed system by the partial recycling of expired air with simultaneous absorption of CO2. During the inspiration phase only a maximum of 42% relative humidity at a temperature of 24.8 degrees C was reached. These values lie far below the demands of the American National Standard Institute (ANSI) of 70% relative humidity at 30 degrees C. When various heat and moisture exchangers were used, the relative humidity improved to 99% at a maximum temperature of 30.3 degrees C (HME Edith; Engström Corporation). The maximum values of the BB 12-15, Pall Corporation, and SH 150 from Siemens were slightly lower. A marked fall was noticed when using the Humid Vent I of the Medimex Corporation, especially in the initial phase. An improved version, the Humid Vent II, has been produced. Physiological values (37 degrees C, 100% relative humidity) are not achieved by any heat and moisture exchangers. This problem could possibly be solved by using infra-red light when warming the gases.

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