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Wakefulness during general anaesthesia was assessed by the isolated forearm technique in two groups of patients for Caesarean section. The anaesthetic was based on the use of oxygen 66%, nitrous oxide 33% and halothane 0.4% during the induction delivery interval. There was a highly significant reduction in wakefulness in the Group who received nitrous oxide at 66% for the first 3 min only. The wakefulness was amnesic in all cases.

A patient became wakeful during a general anaesthetic for Caesarean section. The isolated forearm technique for assessing wakefulness was in use. In response to questioning, the patient indicated by hand signals her wish to remain awake. She felt no pain. After the operation she was able to remember the experience, being told about the delivery, and hearing her baby cry. The words from a tape-recording of the anaesthetist's postoperative visit on the next day are presented.

Measurements of maternal blood-gas tensions, (PAO2-PaO2), calculated pulmonary venous admixture (physiological shunt) and deadspace/tidal volume ratio (VD/VT) were made in 14 patients undergoing Caesarean section. Measurements were carried out after induction of general anaesthesia, and before delivery, with the patient tilted to the left. With a mean inspired oxygen concentration of 67.5% mean PaO2 was 44.3 kPa, mean (PAO2-PaO2) 18.4 kPa, mean Vd/Vt 32% and mean physiological shunt 9.5%. The findings are compared with published values for non-anesthetized pregnant patients.

We examined the feasibility of administering nearly 100% oxygen throughout the induction-delivery period of general anaesthesia for 113 Caesarean sections. Isoflurane 1.25% was compared with 1.5% enflurane for maintenance of anaesthesia. The level of anaesthesia was monitored by use of the isolated forearm technique. There was a greater amount of isolated forearm movement when enflurane was used. The three main criteria for a satisfactory general anaesthetic technique for Caesarean section were fulfilled, namely no maternal awareness, no undue depression of the fetus and no adverse effect on uterine contractility. Isoflurane and enflurane appear to be suitable anaesthetic agents for facilitating hyperoxygenation during Caesarean section.

The management of failure to intubate the trachea during emergency Caesarean section in a 116.7-kg woman is described. General anaesthesia was continued with the aid of a Gordon and Don Michael Esophageal Gastric Tube Airway. The forward displacement of the larynx caused by the tube in the oesophagus improved the patency of the airway.

The effect on halothane uptake of changing the nitrous oxide concentration during the first few minutes of a general anaesthetic for Caesarean section was investigated. In 10 mothers anaesthesia was maintained with halothane 0.4%, nitrous oxide 33% and oxygen 66%. In 10 others the sole difference in anaesthetic technique was that the ratio of nitrous oxide to oxygen was reversed for the first 3 minutes only. Serial maternal arterial blood samples showed a significant increase in halothane levels in the group where the nitrous oxide was increased, with p less than 0.02 at 1 and 2 minutes and p less than 0.05 at 3.4 and 5 minutes. After 5 minutes there was no significant difference between the two groups. Cord blood concentrations between the two groups were comparable. The difference in halothane levels is a demonstration of the influence of the concentration effect of nitrous oxide on the uptake of halothane, the second gas effect. The relevance of anaesthetic uptake to obstetric anaesthesia and awareness is discussed.