• P Biro.
• Institut für Anästhesiologie, Universitätsspital Zürich.
• Anaesthesist. 1993 Sep 1;42(9):638-43.

AbstractA marked decrease in both personal and environmental pollution with anaesthetic gases as well as in costs is possible with anaesthesia machines which can be run with a low fresh gas flow (FGF) [9]. Low-flow anaesthesia can be performed with appropriately equipped circle systems, although strongly reduced FGF minimises the control of depth of anaesthesia and gas concentrations. Microprocessor-controlled feedback systems allow the utilisation of closed-circuit systems throughout the whole duration of anaesthesia, maintaining full anaesthetic control [3,5]. The aim of this investigation was to determine the costs resulting from gas consumption and clinical suitability of the recently marketed PhysioFlex anaesthesia machine. METHODS. We used a PhysioFlex (Physio, Hoofdorpp, Netherlands) in a series of 15 routine otorhinolaryngological interventions. After induction with thiopentone and suxamethonium, general anaesthesia was maintained with nitrous oxide in 30% oxygen 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 uptake and costs were compared with different breathing systems (low-flow anaesthesia, semiclosed system and non-rebreathing system) under similar 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) l/h and 0.27, isoflurane 3.9 ml/h and SFr. 5.42. In contrast, other breathing systems in analogous settings resulted in greater costs 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 emission of anaesthetic gases can be lowered by measures that avoid unintended gas fallout, 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 patient insofar as better conditioned breathing gases are available, and economic and environmental effects are more significant (Table 3). With the method of quantitative anaesthesia as performed by the PhysioFlex, it is now possible to reduce gas expenditure according to the requirements of the patient as well as maintaining full control of anaesthesia depth. Simultaneously, multiple secured feedback control systems guarantee adequate monitoring and storage of respiratory and metabolic parameters. The duration of nitrous oxide wash-out can be a problem, in particular, when a changeover to O2/air is required.

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