Closed system enflurane in oxygen

A safe method of administering enflurane from a Goldman vaporizer in a closed system is described, using a fresh gas flow of 0.5 litres minute of oxygen. There was a drawback, in that, until the system was closed, insufficient concentration of enflurane was achieved in seven out of 20 patients, who then moved on surgical incision. When the system was closed, the concentration of enflurane increased so that satisfactory anaesthesia occurred. The maximum inspired concentration of enflurane in the system was 4.5% which occurred in one patient on the 3rd notch of the Goldman. A portable interference refractometer was used to measure the percentage of enflurane.