Methoxyflurane and nitrous oxide as obstetric analgesics. I. A comparison by continuous administration.

Methoxyflurane and nitrous oxide have been compared as obstetric analgesics. The inhaled concentrations of these agents, given continuously, were adjusted by an anaesthetist to maintain each patient at the optimum state between reaction to pain and consciousness. Assessments were made continuously.Though the anaesthetist's assessment showed no difference between the mean results, a greater proportion of the methoxyflurane patients were "satisfactory" for 90-100% of the time than of the nitrous oxide patients, particularly in regard to objective pain relief. The midwives' opinion of those who had "complete" pain relief supported this. Nausea was significantly less among methoxyflurane patients, and vomiting during labour occurred only in patients who had nitrous oxide. It is concluded that nitrous oxide and methoxyflurane given in a continuously adjusted concentration are almost equally effective as obstetric analgesics, though there are certain features which favour methoxyflurane.