Controlled Ventilation Using the Lack Circuit with an Injector Device

A Lack breathing system with an injector device has been used for controlled ventilation. Oxygen was delivered through an injector device, which was positioned between the Lack circuit and the catheter mount, whilst nitrous oxide was delivered from the anaesthetic machine. The circuit was fully tested on two model lungs. Satisfactory tidal volumes were obtained and with fresh gas flow rates of about 4 l X min-1, rebreathing was not detected. The circuit was then studied on ten patients undergoing surgery and it was found that an end-tidal carbon dioxide concentration of 5-6% could be maintained. The use of this system during general anaesthesia is discussed.