Analysis of an anaesthetic gas scavenging system hazard.

The collapse of the reservoir bag in a circle circuit was observed during anaesthesia. This resulted from the incomplete closure of the pressure relief valve on the absorber whie it was connected to the scavenging system. Although the scavenging system was operating and installed according to the manufacturer's recommendations and to the CSA standard on Anaesthetic Gas Scavenging Systems (Z168.8), the patient was not protected from this hazard. Introducing an air break into the scavenging interface device will protect the patient. However, such a system would not meet the CSA standard and would make the relief valves on the scavenging interface device unnecessary.