Cryotherapy gas - to use nitrous oxide or carbon dioxide?

Cryotherapy is regularly used in our clinic for treating genital warts. Nit rous oxide was used as the cryogenic gas. Following a health and safety rev iew it was decided to monitor the nitrous oxide levels in the treatment roo m under different conditions. The Occupational Exposure Standard for nitrou s oxide is 100 parts per million (PPM) (8-h time weighted average) and an i ndicative short-term exposure limit of 300 PPM (15-min reference period). H igh levels of gas were detected, especially when the exhaust was not vented to the outside. Venting of the gas to the outside could also present a haz ard to adjacent areas. The situation was considered to be unacceptable and carbon dioxide was proposed as an alternative. The Occupational Exposure St andard for carbon dioxide is 5000 PPM (8-h time weighted average) and a sho rt-term limit of 15,000 PPM (15-min reference period). Carbon dioxide level s were found to be within the Occupational Exposure Standard. There is no n oticeable difference in the cryogenic efficacy of the 2 gases. Carbon dioxi de is, therefore, a safer alternative. It also offers significant savings w hen compared with nitrous oxide.