Nitrous-oxide analgesia during ambulance transportation. Airborne levels of nitrous oxide.

A model experiment was performed for studying nitrous-oxide levels in the breathing zones of the different members of an ambulance team, viz. the anesthetist, the accompanying person in the ambulance coupé, and the ambulance driver. Without a functioning local exhaust coupled to the exhalation valve, the integrated average level of nitrous oxide in the breathing zone of the anesthetist was 650-1,700 ppm, with top concentrations up to 7,500 ppm. Under the same conditions, the accompanying person in the ambulance coupé was exposed to average concentrations of 58-280 ppm, with top concentrations up to 660 ppm. The mean exposure of the driver was 9-45 ppm (max. 81 ppm). However, the exposure to nitrous oxide was considerably decreased in all parts of the ambulance by an effective local exhaust system. A prerequisite for nitrous-oxide analgesia in ambulances is an effective local exhaust coupled to the exhalation valve or face mask. The ambulance coupé ought to be equipped with a motor-driven exhaust fan in the roof, the ordinary inlet fan of the ambulance should be switched on at maximum speed, and any additional heater or fan in the ambulance coupé should be placed inside the coupé and not behind the driver's seat.