Cryotherapy Gas — to Use Nitrous Oxide or Carbon Dioxide?

Abstract

Cryotherapy is regularly used in our clinic for treating genital warts. Nitrous oxide was used as the cryogenic gas. Following a health and safety review it was decided to monitor the nitrous oxide levels in the treatment room under different conditions. The Occupational Exposure Standard for nitrous oxide is 100 parts per million (PPM) (8-h time weighted average) and an indicative short-term exposure limit of 300 PPM (15-min reference period). High 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 hazard to adjacent areas. The situation was considered to be unacceptable and carbon dioxide was proposed as an alternative. The Occupational Exposure Standard for carbon dioxide is 5000 PPM (8-h time weighted average) and a short-term limit of 15,000 PPM (15-min reference period). Carbon dioxide levels were found to be within the Occupational Exposure Standard. There is no noticeable difference in the cryogenic efficacy of the 2 gases. Carbon dioxide is, therefore, a safer alternative. It also offers significant savings when compared with nitrous oxide.

Efficacy and Safety of Three Cryotherapy Devices for Wart Treatment: A Randomized, Controlled, Investigator-Blinded, Comparative Study

“…Therefore, initial temperature of the applicator of the cryogenic device must be low enough to achieve such temperature in the lower layers of the infected area. The concept of the test product, combining a specific polyurethane nib as applicator, guaranteeing optimal skin contact, and nitrous oxide as cooling agent, allows the device to reach an in vitro freezing temperature of − 80 °C, which can be maintained for a period of 60 s. This temperature lies between the boiling point of liquid nitrogen (196 °C) and the boiling point of the gases, used in the comparator devices: DME (− 24 °C) and DMEP (− 57 °C), respectively [ 11 , 16 , 17 ]. The significant difference in temperature may explain why the comparator products showed lower cure rates in the present trial.…”

“…However, there is a substantial difference in the freezing temperature that both devices are capable to reach. Nitrous oxide boils at − 87 °C, in between the boiling point of liquid nitrogen (− 196 °C) and DMEP (− 57 °C) [ 11 , 16 , 17 ]. In the past, several reports have questioned whether DMEP matches the clinical efficacy of liquid nitrogen.…”