The use of 0.25% isoflurane premixed in 50% nitrous oxide and oxygen for pain relief in labour

The addition of 0.25% isoflurane to 50% nitrous oxide in oxygen provides mo re effective pain relief in labour than 50% nitrous oxide alone. This study was carried out to determine whether self-administration by demand valve o f 0.25% isoflurane in 50% nitrous oxide in oxygen premixed in cylinders at 13.7 MPa (IN2O) was practical and safe during labour. Two hundred and twent y-one mothers used INO in labour after 50% nitrous oxide had become inadequ ate for pain relief. Data on IN2O use was recorded during labour and detail s of the course of labour and opioid usage were taken from the clinical not es. The duration of IN2O use was 0.1-12:35h (median 2.3). Thirty-two mother s (14.5%) required an epidural and intolerance to IN2O was seen in a maximu m of 17 cases (7.7%). One hundred and twenty-six cases were primiparous and 93 parous with 151 deliveries being spontaneous and 70 interventional, of which 12 were by Caesarean section. Maternal blood loss was 20-1500 ml (med ian 200 ml). Apgar scores at 1 and 5 min were unaffected by IN2O use althou gh a positive correlation was found between the use of opioids and the numb er of neonates with a 1-min score below 8 and the number requiring resuscit ation; Six neonates had an Apgar score below 8 at 5 min, but their conditio n was adequately explained by factors other than the sedative technique use d. Self-administered IN2O was found to be a safe and practical technique fo r sedation in labour when 50% nitrous oxide alone had become inadequate.