Nitrous oxide levels in operating room air with various gas flows

Monitoring of nitrous oxide concentrations in operating rooms disclosed some leaks that had hitherto been unrecognized. Because nitrous oxide concentrations reported before 1967 had been obtained for the most part with high flows of the gas and without information concerning room air exchange, measurements were made of nitrous oxide levels during operations with an infra-red analyzer. after correction of leaks. Measurements were made at six sites in the operating-room suite, with and without scavenging. Flows that varied 0.1 to 2.5 litres of nitrous oxide were used in rooms that had 20 changes per hour of fresh air. Without scavenging, the highest time-weighted average value inhaled by any of the personnel (anaesthetists) was 31 ppm, when flow of 500 ml of nitrous oxide per minute were employed. The lowest reported deleterious concentration (unconfirmed) is 50 ppm. Lower flows produced lower values. With good scavenging, using flows as high as 2.51/min of nitrous oxide, the highest average value (anaesthetist) was 7.2 ppm. A short discussion is given concerning reasons for using low flows, including the cost of wasting agents and pollution of the entire atmosphere.