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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.

The effects of 0.08% (Group A) and 0.25% (Group B) solutions of bupivacaine were compared in a random manner, to assess continuous pump infusion epidural analgesia in labour. Both solutions were infused at a dose rate of 20 mg bupivacaine/hour. The results in all the mothers who had received infusions lasting more than 4 hours were studied. There were 25 in Group A and 28 in Group B. Any treatment during the infusion epidural for inadequate analgesia, hypotension, etc., was recorded as an intervention. The mean of the intervention-free intervals was significantly greater in Group A than in Group B, and significantly fewer top-up injections were required in Group A. The results show that the administration of a 0.08% solution of bupivacaine into the epidural space by continuous pump infusion is more labour saving than the infusion of a 0.25% solution. The concept that a greater volume infusion rate maintains a more extended liquid sleeve of local anaesthetic in the epidural space is supported.

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.

Entonox (50% nitrous oxide in oxygen) and isoflurane (0.75% in oxygen) were compared as analgesics in the first stage of labour in 32 consenting women. The drugs were self-administered and given in random sequence, each during five consecutive uterine contractions. Each patient acted as her own control. Linear analogue pain scores were significantly lower (p less than 0.001) with isoflurane than with Entonox, but scores for drowsiness were higher for isoflurane. Further study is needed to assess the effects of more prolonged use of isoflurane in labour.

The need is identified of certain women in labour for a more potent analgesic than entonox. We describe a modification of the Entonox demand system incorporating an Oxford Miniature Vaporizer and there is a discussion directed towards its supervision.

The outcome of 175 pregnancies during which nitrous oxide was administered has been evaluated. All anaesthetics were of short duration (20-30 min) and 97% were administered during the second trimester. No adverse effects were identified. The mechanism of potential toxicity and the implications of the use of nitrous oxide during the first and second trimesters of pregnancy are discussed.

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 effects of 0.08% and 0.5% bupivacaine, given in equal volumes as the loading dose prior to continuous infusion epidural analgesia, were compared. The incidence of hypotension, as well as the height of sensory blockade, was markedly lowered by reducing the loading dose of bupivacaine. However, the efficacy of the epidural analgesia was maintained by using the same volume for the loading dose. The mean onset of analgesia was delayed from 9.1 to 13.6 minutes. There were fewer calls for intervention consequent upon the reduction in adverse effects. The use of 8 ml 0.08% bupivacaine for the loading dose or for subsequent top-ups is recommended. The concept of a liquid sleeve of local anaesthetic in the epidural space is further supported.

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.