(Part 2) Economic aspects of concentration-oriented anaesthesia: halogenated agents

Wastage of halogenated agents is correlated to the rate of fresh-gas flow (FGF) into the anaesthetic circuit. An overall reduction in FGF allows a decrease in the cost of inhalation anaesthesia. Low-flow anaesthesia is economically advantageous but it prevents the rapid establishment of a useful alveolar concentration and intra-operative adjustment of depth of anaesthesia. Both calculations and modelling have shown that FGF has to be transiently increased either to establish alveolar concentrations or to allow adaptation to surgical stimulations, even with maximum vaporizer settings. Closed circuit anaesthesia requires the injection of halogenated agents into the circuit, as occurs in the PhysioflexTMmachine. The PhysioflexTMmachine uses a closed circuit that is washed out by a blower. A computer regulates the gas flows and the agent injection in order to maintain end-tidal concentrations at a predetermined level. A charcoal filter allows circuit agent concentration to be decreased without changing the FGF. This system allows a reduction of costs and a precise and rapid control of anaesthesia.