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 concentrations of ambient anesthetic gases have not been evaluated fully during routine circumstances, however. Methods: Concentrations of nitrous oxide (N 2 O) in ambient air were monitored automatically in 10 operating rooms in Kagoshima University Hospital from January to March 1997. Ambient air was sampled automatically from each operating room, and the concentrations of N 2 O were analyzed every 22 min by an infrared spectrophotometer. The output of the N 2 O analyzer was integrated electronically regarding time, and data were displayed on a monitor in the administrative office for anesthesia supervisors. A concentration of N 2 O > 50 parts per million was regarded as abnormally high and was displayed with an alarm signal. The cause of the high concentration of N 2 O was then sought. Results: During the 3-month investigation, N 2 O was used in 402 cases. Abnormally high concentrations of N 2 O were detected at some time during 104 (25.9%) of those cases. The causes were mask ventilation (42 cases, 40.4% of detected cases), unconnected scavenging systems (20 cases, 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: N 2 O contamination was common during routine circumstances in our operating rooms. An unconnected scavenging system led to the highest concentrations of N 2 O recorded. Proper use of scavenging systems is necessary if contamination by anesthetic gas is to be limited.