A new ventilator for closed breathing systems.

A new electronic ventilator for application during closed breathing system anaesthesia is described (OAV7700, Ohmeda). It is easy to use and can be mounted on any conventional anaesthetic machine. It has several desirable features, such as a simple control and display panel, appropriate alarms and a patient breathing system that can be autoclaved. Observations were made on seven patients undergoing major surgery. Anaesthetic gases were introduced at 1, 2 and 4 litres/minute at three points in the breathing system, one conventionally in the closed system, one at the ventilator and one in the tracheal tube. Carbon dioxide homeostasis was maintained during this procedure. The application of fresh gas flows of 2 and 4 litres/minute in the tracheal tube allowed a small but significant reduction in the mean tidal volume. However, it was concluded that a fresh gas flow of 1 litre/minute applied conventionally either into the closed system or at the ventilator, provided optimal conditions.