Efficiency of a circle system for short surgical cases: comparison of desflurane with isoflurane

Patients undergoing short surgical procedures but requiring ventilation of the lungs were allocated randomly to receive either desflurane or isoflurane by circle absorption system, initially at a high fresh gas flow. The inspired and expired concentrations of the volatile agent were measured and the fresh gas flows reduced to low flow (500 ml min-1 total when FE/FI = 0.8), as measured on a multigas analyser. In patients receiving desflurane (n = 32), the median time at which flows were reduced was 5 min (interquartile range (IQR) 1 min) while with isoflurane (n = 32), the median time was 19 (IQR 12) min. After the reduction in flow, expired concentrations of volatile agent decreased in both groups. In the isoflurane group the concentration continued to decrease during anaesthesia. In the desflurane group the initial decrease was followed by a slow recovery. We conclude that the circle system can be used efficiently for short anaesthetics using desflurane.