Nitrous oxide contamination during out-patient cryosurgery.

Nitrous oxide concentrations have been measured spectrophotometrically in an out-patient clinic to assess pollution during simulated cryosurgery. Unacceptable levels, in excess of 2,000 ppm, were achieved during freezing and thawing and concentrations decreased only to 400 ppm when simple measures were taken to ventilate the clinic. The apparatus required a flow-rate of 11 l/min. It is concluded that scavenging apparatus should be used during cryosurgery with nitrous oxide if treatment is prolonged. Liquid nitrogen systems are preferable if excellent ventilation and scavenging apparatus are not available.