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SummaryThe elimination of nitrous oxide by ten infants whose mothers had received50X nitrous oxide in oxygen and enflurane 0.6-1% during general anaesthesia for Caesarean section was studied. The concentration of nitrous oxide detected in end-expiredgas rangedfrom I to 4 vol% (mean 1-9 vol%/ . These levels are too low to produce signifcant diffusion hypoxia in vigorous neonates. However, a minority of infants may be adversely aflectedand it is recommended that oxygen-enriched air be administered to infants whose mothers have received nitrous oxide. Key wordsAnaesthetics; gases; nitrous exide. Anaesthesia; obstetric.The newborn human infant must, within moments of entering a new and hostile environment, initiate certain vital physiological changes to ensure adequate tissue perfusion and cellular oxygenation. The initial cry of an apparently lusty infant, delivered at Caesarean section performed under general anaesthesia, may be followed by apnoea. Several causes have been postulated for this occurrence, including laryngeal inhibition as a result of vigorous pharyngeal toilet,' frothing: diffusion hypoxia3 and nitrous oxide n a r c~s i s .~ Attempts have been made to demonstrate diffusion hypoxia in the neonate, with conflicting result^.',^ As apnoea after satisfactory initial respiration has not been observed by us following Caesarean section performed under epidural anaesthesia, it seemed appropriate to re-investigate the role of diffusion hypoxia in neonatal apnoea. MethodsTen infants of mothers presenting for repeat elective Caesarean section for cephalo-pelvic disproportion were studied. All the infants were mature as judged by clinical appraisal and X-ray or amniocentesis. The mothers were all in good health and there was no evidence of placental insufficiency in any of the cases studied. The anaesthetic technique used has been described elsewhere.' The salient features, prior to the birth of the infant, are the use of left lateral tilt, preoxygenation, administration of metoclopramide 10 mg and alcuronium 2.5 mg intravenously, followed by induction of anaesthesia with thiopentone 3.5 mg/kg plus suxamethonium 150 mg. Cricoid pressure is applied and the trachea rapidly intubated. The patient's lungs are ventilated with 50% nitrous oxide (NzO) in

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