Oxygenation of the foetus is probably the most important single environmental factor which has a bearing upon the eventual well-being of the infant. Throughout pregnancy imperfect oxygenation is inimical to continued viability. At delivery, inadequate oxygenation can jeopardize the baby's immediate survival. Hypoxia, not severe enough to cause immediate or neonatal death can result in permanent neurological damage.At caesarean section it is possible to control the conditions of oxygen administration to the mother accurately and at the same time to observe the effect of this upon the maternal and foetal blood. This study was designed to investigate the effects of various inspired maternal oxygen concentrations on babies delivered by elective caesarean section, inspired oxygen concentration being the only variable. MIITHODThirty-four women at term (38 to 42 weeks gestation) were studied. They were undergoing caesarean section under general anaesthesia for either cephalo-pelvic disproportion or previous caesarean section. All the mothers were healthy by clinical, radiological and biochemical assessment as regards cardiovascular, respiratory and urinary systems and the course of their pregnancies was uncomplicated. During the hours preceding operation each was given about one litre (700 to 1350ml) of 10% invert sugar in Ringer Lactate to minimise the effect of overnight starvation on metabolism.Immediately prior to induction of anaesthesia, arterial blood was taken anaerobically into a heparinized glass syringe by discrete puncture of the radial artery. Intravenous atropine 0.65mg was given just before induction with an appropriate hypnotic dose of thiopentone. Following suxamethonium 50mg the trachea was sprayed with 4 % lignocaine and then intubated with a 9.0mm cuffed Magill endotracheal tube. The cuff was optimally inflated to prevent gas leaks. Intermittent positive pressure ventilation was imposed using the non-return circuit of an Engstrom ventilator. A M .

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