Measurement and reduction of nitrous oxide in operating rooms.

In a program designed to lower exposure to anesthetic gases, nitrous oxide in the breathing zone of anesthesiologists was continuously monitored by means of a direct reading apparatus and a specially designed collar. Initially, the average concentration during anesthesia in intubated patients, determined in 30 operating rooms of seven hospitals, was 68 ppm. During mask anesthesia in children, it was 407 ppm (nine operating rooms, nine hospitals). The main hygienic measures were: a check of the anesthesia apparatus, improvement of the general ventilation in the operating room, and the application of a "double mask." With a combination of measures, the concentration during anesthesia in intubated patients was reduced from 61-90 ppm to 2-15 ppm. During mask anesthesia in children, the concentration decreased from 134-764 ppm to 9-42 ppm. The monitoring system used reveals important differences in the exposure during the separate phases of the anesthesia (induction, maintenance, and extubation). It also indicates which factors determine the exposure of the anesthetist and allows accurate determination of the personal exposure.