Entonox analgesia in labour. A pilot study to reduce the delay between demand and supply.

In a pilot study in six mothers using 50% nitrous oxide and 50% oxygen (Entonox) as an intermittent self-administered analgesic during labour, a significant reduction in the mean times to attain specified end-tidal nitrous oxide concentrations was obtained by a continuous nasal supplement of Entonox. The method proved acceptable in this small number of patients and there were no demonstrable effects upon fetal heart rate.