The uptake of isoflurane during anaesthesia

The uptake of isoflurane at a constant end-expired concentration of 1.5% in oxygen was studied in 15 women, ASA 1 or 2, undergoing elective total abdominal hysterectomy. The anaesthetic was administered by a simple computer-controlled to-and-fro closed system. After an initial period of wash-in to the system, the rate of uptake of isoflurane decreased bi-exponentially with a rapid reduction during the first 15 min. Perturbations from this bi-exponential decline reflect changes in cardiac output. The mean (SD) cumulative use of isoflurane was 4.5 (0.43) ml after 30 min and 7.3 (0.79) ml after 60 min.