Tolerance to Nitrous Oxide in Volunteers

Abstract

Nociception and loss of awareness during exposure to anaesthetic concentration of nitrous oxide (N2O) were studied in eight male medical students. The cold water nociception test, where a hand is immersed in 0 degree C stirred water, was used for measurement of nociception. At irregular intervals an auditory command was given to oppose two fingers, and this served to monitor consciousness. The selected inspiratory concentration of N2O used per individual was sufficient to induce a loss of consciousness for more than 2.5 min, within 10 min of exposure to N2O. This concentration of N2O varied from 60% to 80%. The experimental exposure to N2O lasted 3 h. In all volunteers significant antinociception was observed within 2 min of exposure to N2O. The maximal analgesic effect was observed between 20 and 30 min of exposure to N2O. The analgesic effect of N2O gradually decreased and was absent in all eight volunteers within 150 min. Two volunteers regained consciousness at 77 and 91 min of exposure, whilst still breathing 60 and 80% N2O. These results show that tolerance to antinociceptive effects of N2O in man rapidly develops and that awareness may occur in some volunteers during prolonged exposure to N2O.

Nitrous oxide added at the end of isoflurane anesthesia hastens early recovery without increasing the risk for postoperative nausea and vomiting: a randomized clinical trial

“…It then gradually decreased and was completely absent in all volunteers within 150 min. 17 There are several limitations in our study. First, this study was conducted in a single centre with only one type of surgical procedure, the duration of which was about two hours.…”

Comparison of the analgesic potency of xenon and nitrous oxide in humans evaluated by experimental pain

“…Several studies using up to 10 min administration of up to 50% nitrous oxide reported no nausea and vomiting. [34][35][36] Rupreht and colleagues 37 found a high incidence of nausea (six of eight volunteers) and vomiting (number not reported) in volunteers breathing 60-80% nitrous oxide for at least 45 min. In our volunteers, nausea quickly vanished after discontinuation of nitrous oxide or xenon.…”

Nitrous oxide analgesia in humans: acute and chronic tolerance

“…Humans develop acute tolerance to anesthetic concentrations of N 2 O (Rupreht et al, 1985). Similarly, when N 2 O is combined with other anesthetic drugs to cause anesthesia, tolerance develops to N 2 O on an electroencephalographic measure (Avramov, et al, 1990).…”