Measurement of the rates of nitrous oxide uptake and nitrogen excretion in man.

Using a completely closed anaesthetic circuit, nitrous oxide uptake and nitrogen excretion were measured simultaneously in patients undergoing nitrous oxide in oxygen anaesthesia for abdominal surgery. The results have been compared with standard models of uptake and excretion. Mean nitrous oxide uptake was measured and did not exceed 400 ml min-1 (normalized to 70-kg man) and was not less than 60 ml min-1 at 100 min after the start of nitrous oxide in oxygen anaesthesia. Nitrogen excretion did not exceed 100 ml min-1 and was measurable (8 ml min-1) at 100 min. The persistence of nitrogen excretion contrasts with other published data obtained with intact volunteers and this suggests that exposure at surgery of abdominal tissues, including fat, affects substantially the rates of excretion and uptake after 70 min.