FRESH GAS UPTAKE IN THE CLOSED-CIRCUIT AN ESTHESIA MACHINE PHYSIOFLEX(R)

A marked decrease in both personal and environmental pollution with an aesthetic gases as well as in costs is possible with anaesthesia machi nes which can be run with a low fresh gas flow (FGF) [9]. Low-flow ana esthesia can be performed with appropriately equipped circle systems, although strongly reduced FGF minimises the control of depth of anaest hesia and gas concentrations. Microprocessor-controlled feedback syste ms allow the utilisation of closed-circuit systems throughout the whol e duration of anaesthesia, maintaining full anaesthetic control [3, 5] . The aim of this investigation was to determine the costs resulting f rom gas consumption and clinical suitability of the recently marketed PhysioFlex(R) anaesthesia machine. Methods. We used a PhysioFlex(R) (P hysio, Hoofdorpp, Netherlands) in a series of 15 routine otorhinolaryn gological interventions. After induction with thiopentone and suxameth onium, general anaesthesia was maintained with nitrous oxide in 30% ox ygen and isoflurane and supplemented with fentanyl and atracurium. The expenditure of anaesthetic gases was recorded during a total of 61 h and 27 min and differentiated into its components. Anaesthetic gas upt ake and costs were compared with different breathing systems (low-flow anaesthesia, semiclosed system and non-rebreathing system) under simi lar clinical conditions. Results. The average minute volume was 6.84 ( +/- 1.17) l and the expiratory isoflurane concentration was 0.91% (+/- 0.14%) (Table 1). These settings resulted in an oxygen expenditure of 27.9 (+/- 8.46) l/h with total costs of SFr. 0.04, nitrous oxide 11.9 (+/- 5.4) 1/h and 0.27, isoflurane 3.9 ml/h and SFr. 5.42. In contras t, other breathing systems in analogous settings resulted in greater c osts by a factor of 0.77 for low-flow anaesthesia (FGF 1 l/min), 2.47 for a semiclosed system (FGF 3 l/min) and 5.63 for a valve-controlled non-rebreathing system (FGF 6.84 l/min) (Table 2). Discussion. The emi ssion of anaesthetic gases can be lowered by measures that avoid unint ended gas fall-out, the application of filters, scavenging systems and efficient air circulation in operation and recovery rooms [8]. Above all, the use of the lowest possible FGF is advantageous for the patien t insofar as better conditioned breathing gases are available, and eco nomic and environmental effects are more significant (Table 3). With t he method of quantitative anaesthesia as performed by the PhysioFlex(R ), it is now possible to reduce gas expenditure according to the requi rements of the patient as well as maintaining full control of anaesthe sia depth. Simultaneously, multiple secured feedback control systems g uarantee adequate monitoring and storage of respiratory and metabolic parameters. The duration of nitrous oxide wash-out can be a problem, i n particular, when a changeover to O2/air is required.