Résumé
Background. Intraoperative discomfort during spinal anaesthesia for Caesarean section is the commonest cited anaesthetic cause of litigation in obstetric practice. Intrathecal opioids are used to improve intraoperative comfort and postoperative analgesia for these operations. The minimum intrathecal diamorphine dose that prevents intraoperative supplementation requires determination
Method: After ethics committee approval, 200 ASA I, II women with 37 weeks gestation and planned for elective Caesarean section under combined spinal epidural anaesthesia were recruited. They were randomize into four groups to receive 1 hyperbaric bupivacaine 0.5% 12.5mg with diamorphine 0.2, 0.3, 0.4 or 0.5 mg by intrathecal injection. The need for intraoperative i.v. supplementation with alfentanil, time to first requests for postoperative analgesia, incidence of nausea and vomiting and requirement for antiemetic and antipruricic were noted
Results: Intraoperative supplementation was inversely proportional to the dose of diamorphine used [P=0.004]. The ED95 value for intrathecal diamorphine to prevent intraoperative supplementation was 0.39 mg. Mean time interval for request for postoperative analgesia was 446 min in the 0.2mg group, 489 min in the 0.3 mg group, 601 min in the 0.4 mg group and 687 min in the 0.5 mg group [P=0.003 for trend]. Incidence of nausea, vomiting and pruritus increased with dose of diamorphine used [P values for trend: nausea, 0.04, vomiting, 0.008; pruritus, 0.004]. Requests for antiemetic increased with dose but achieved significance only for requirement for second antiemetic [P = 0.03]. Request for antipruritic did not achieve significance
Conclusion. The ED95 for the amount of intrathecal diamorphine required to prevent intraoperative supplemnentation during spinal anaesthesia for Caesarean section is 0.4 mg in clinical terms. Times to first requests for analgesia, incidence of nausea, vomiting and pruritus increase with dose