Causes of nitrous oxide contamination in operating rooms

Background To reduce the ambient concentration of waste anesthetic agents, exhaust gas scavenging systems are standard in almost all operating rooms. The incidence of contamination and the factors that may increase the concen trations of ambient anesthetic gases have not been evaluated fully during r outine circumstances, however. Methods: Concentrations of nitrous oxide (N2O) in ambient air were monitore d automatically in 10 operating rooms in Kagoshima University Hospital from January to March 1997, Ambient air was sampled automatically from each ope rating room, and the concentrations of N2O were analyzed every 22 min by an infrared spectrophotometer, The output of the N2O analyzer was integrated electronically regarding time, and data were displayed on a monitor in the administrative office for anesthesia supervisors. A concentration of N2O > 50 parts per million was regarded as abnormally high and was displayed with an alarm signal. The cause of the high concentration of N2O was then sough t. Results: During the 3-month investigation, N2O was used in 402 cases, Abnor mally high concentrations of N2O were detected at some time during 104 (25. 9%) of those cases. The causes were mask ventilation (42 cases, 40.4% of de tected cases), unconnected scavenging systems (20 cues, 19.2%), leak around uncuffed pediatric endotracheal tube (13 cases, 12.5%), equipment leakage (12 cases, 11.5%), and others (17 cases, 16.4%). Conclusions: N2O contamination was common during routine circumstances in o ur operating rooms, An unconnected scav enging system led to the highest co ncentrations of N2O recorded, Proper use of scavenging systems is necessary if contamination by anesthetic gas is to be limited.