SummaryThe effects of pre-oxygenation were studied by continuous expired oxygen analysis in twenty pregnant patients and ten nonpregnant controls. The Magill system and a demand valve breathing system were both studied with tidal and vital capacity breathing. Rapid pre-oxygenation Most of the published work on the effects of preoxygenation has concerned the nonpregnant general surgical patient.' , 2 We feel. however, that the pregnant patient deserves special attention for thrcc reasons. First, pre-oxygenation ha5 become a standard feature in the rapid sequence induction of general anaesthesia for Caesarean section. Second. in the acute obstetric emergency. failure to achieve maximum pre-oxygenation can have grave consequences. Third. term pregnancy is associated with changes in lung volumes and function. The mean tidal volume is increased by about 40% over values found in the nonpregnantT3 due probably to progc~tcrone.~ Upward displacement of the diaphragm by the gravid uterus causes a reduction in functional residual capacity (FRC) to 9.5-25'1i0 below the values obtained in nonpregnant s~b j e c t s .~.~,~ The reduction in FRC associated with rclative alveolar hypcrventilation should facilitate rapid pre-oxygenation prior to Caesarean section.Two breathing systcms were invcstigated. One was a system that incorporates both demand and non-rebrcathing valves similar to the standard F.ntonox apparatus. This permits a pcak inspiratory flow of 500 litres/minute without rebreathing of expired gas. As such. it should theoretically be the ideal systcm for preoxygenation. The Magill system was also investigated because it is probably the breathing system most widely used for pre-oxygenation in the United Kingdom.

The incidence of severe muscle pain following Caesarean section in 130 patients in which suxamethonium was used was 15.7 per cent. Gallamine 20 mg prior to induction did not reduce the incidence of pain but resulted in technical difficulty which reduced the safety and effectiveness of the anaesthetic technique. It was concluded that the incidence of pains was not high enough to justify discarding the anaesthetic technique described. The use of non-depolarizing relaxants prior to induction as a method of reducing the incidence of pains following suxamethonium should be avoided in obstetric anaesthesia.

In a double-blind trial in 28 human volunteers, a new local anaesthetic agent, aptocaine, was compared intradermally at 1, 2 and 3% concentrations with lignocaine 2% and bupivacaine 0.5%. In a second trial in 27 subjects, 1% aptocaine was compared with mepivacaine and prilocaine, both 1, 2 and 3%. In terms of activity as determined by area of anaesthesia, and of duration of action, aptocaine was similar to mepivacaine and more active and long-lasting than lignocaine and prilocaine. By this route aptocaine also appeared longer-lasting than bupivacaine. Duration of action was unaffected by concentration. Aptocaine had marked vasoconstrictor activity, which was maximal at 1%. These local anaesthetic properties suggest that aptocaine merits clinical trials, especially in dentistry.

Summary Epidural injections of morphine (2·5 or 4 mg) were given to 25 patients in labour. Forty‐eight per cent had good relief of pain lasting from 3¼ to 11 hours (average 5¼ hours). Sixteen per cent of patients had transient or partial relief, and in 36% there was no discernible effect at all. No serious side effects were observed in either mother or baby. It is felt that this technique merits further investigation in view of its potential advantages over more traditional methods of pain relief in labour.