[Fresh gas flow and artificial respiration in anesthesia. Technical requirements for the adequate use of rebreathing systems]

Abstract

The majority of modern anaesthetic machines is designed for the rebreathing method. But frequently high fresh gas flows are employed, thus minimising the rebreathing fraction of expiratory gases. However, only by reducing the fresh gas flow substantially, the advantages of the rebreathing technique can be obtained. To evaluate the practicability of flow reduction, minimal flow anaesthesia was carried out with four different anaesthetic machines: AV 1 (Drägerwerk AG, Lübeck), ELSA (Gambro Engström AB, Bromma, Sweden), SULLA 808 V (Drägerwerk AG, Lübeck) und VIVOLEC (Hoyer Medizintechnik, Bremen). Fresh gas flow was reduced to 0.5 l/min after an initial phase of 15-20 min, during which the fresh gas flow was kept at a high level of 4.4 l/min. The minute volumes before and after fresh gas flow reduction were compared. The minute volume decreased markedly and significantly in the SULLA 808 group, whereas it remained nearly unchanged in the AV 1, the ELSA, and the VIVOLEC groups. The differences result from different modes of fresh gas delivery into the breathing circuit. If anaesthetic apparatus that maintain their tidal volume with different fresh gas flow rates are employed, rebreathing systems may be used judiciously by changing the fresh gas flow according to the individual uptake or any particular clinical requirement.