The Engström Elsa anaesthetic machine. An electronic system for anaesthesia

Six Engström Elsa anaesthetic machines have been in regular use for 18-24 months. The machine incorporates a number of new concepts for anaesthetic delivery and monitoring. At flows below 1000 ml/minute, each machine delivered 20% more than the indicated value; at higher flows, the indicated value was within 10% of the flow delivered. Minute volume, tidal volumes and oxygen concentrations were within the manufacturer's specifications. However, vaporizer and vapour monitor performance was outside the (SD) 5% accuracy claimed by the manufacturers. It was noted that the bistable valve requires user familiarity for the change from controlled to spontaneous ventilation to be accomplished with ease. It was also possible to misconnect the breathing system and so isolate the excess pressure escape valve and high-pressure alarm. Nevertheless, once familiarisation was achieved, the machines have proved easy to operate and are particularly satisfactory when used with low fresh gas flows.