Uptake of isoflurane during clinical anaesthesia. Servo-control of liquid anaesthetic injection into a closed-circuit breathing system.

Twenty-six patients were anaesthetized with isoflurane (Forane) in oxygen using a completely closed-circuit breathing system to which liquid isoflurane was injected. The rate of injection was controlled to maintain the end-tidal concentration at a pre-set value (1.5% = 1.3 MAC). The rate of injection of anaesthetic was recorded and from the data the uptake of anaesthetic by the patient was measured. It was found to average 44.5 ml of vapour at 2 min, 23.7 ml at 10 min and 19.4 ml at 30 min. Attempts were made to correlate the data with anthropometric measurements.