Controlled ventilation using isoflurane with an in-circle vaporiser

We studied 19 patients anaesthetised for routine surgery using isoflurane delivered from a Komesaroff vaporiser mounted within a circle system. Their lungs were ventilated using a Penlon Nuffield ventilator attached to the circle system by a trunk of tubing. Fresh gas flow rates of 1, 2 or 31.min-1 were used. The inspired agent concentration was measured using a Datex Ultima multigas analyser and was found to be stable and easily controlled.