Isoflurane with either 100% oxygen or 50% nitrous oxide in oxygen for caesarean section

Two hundred mothers undergoing general anaesthesia for Caesarean section were allocated randomly to receive either 100% oxygen (group 100) or 50% nitrous oxide in oxygen (group 50), both supplemented with isoflurane. In each group the concentrations of isoflurane were chosen to deliver 1.5 MAC for the first 5 min after induction and 1.0 MAC thereafter. The mean umbilical venous PO2 was greater in group 100 for emergency sections (P = 0.001). Babies born to mothers in group 100 required less resuscitation than those in group 50 (P = 0.04) and there was a tendency to higher Apgar scores at 1 min in group 100, although this was not statistically significant. There were no instances of awareness, although two patients in group 100 and three in group 50 reported dreaming. This study confirms earlier findings that the use of 100% oxygen can significantly improve fetal oxygenation during Caesarean section, with particular benefit in emergency cases. This is associated with a lower incidence of neonatal resuscitation.