Mechanical ventilation during low-flow anaesthesia. Experience with an alternative to the bag-in-bottle

Clinical experience with low-flow anaesthesia during controlled ventilation of the lungs is described. The anaesthesia circle is separated by a corrugated hose that serves as a large deadspace. This open connexion has no bellows or overflow valve and therefore the risk of mechanical dysfunction is small. No mixing of circle and ventilator gas occurs during normal operation. Major decreases in the oxygen concentration in the system are unlikely even if the fresh gas flow is interrupted or significant leaks from the circle occur because 100% oxygen is delivered by the ventilator. A hose volume larger than 1650 ml prevented gas mixing at tidal volumes of 380-1170 ml. There was no system-related mishap in over 600 patients, who comprised about 40% of the neurosurgical patients anaesthetised during that period. The cost of isoflurane was reduced to about 33% of that incurred during previous periods.