Minimum dose of intrathecal diamorphine required to prevent intraoperative supplementation of spinal anaesthesia for Caesarean section.
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.


METHODS
After ethics committee approval, 200 ASA I, II women with > or = 37 weeks gestation and planned for elective Caesarean section under combined spinal-epidural anaesthesia were recruited. They were randomized into four groups to receive hyperbaric bupivacaine 0.5% 12.5 mg 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 antipruritic were noted.


RESULTS
Intraoperative supplementation was inversely proportional to the dose of diamorphine used (P=0.004). The ED(95) 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 0.2 mg 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.


CONCLUSIONS
The ED(95) for the amount of intrathecal diamorphine required to prevent intraoperative supplementation 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.
Saravanan
S
S
Obstetric Anaesthesia, St James's University Hospital, Leeds, UK.
Robinson
A P C
AP
Qayoum Dar
A
A
Columb
M O
MO
Lyons
G R
GR
D000328:Adult; D015760:Alfentanil / Q000008:administration & dosage; D000701:Analgesics, Opioid / Q000008:administration & dosage* / Q000009:adverse effects; D000767:Anesthesia, Epidural; D000773:Anesthesia, Obstetrical / Q000379:methods*; D000775:Anesthesia, Spinal; D002585:Cesarean Section; D004311:Double-Blind Method; D004334:Drug Administration Schedule; D005260:Female; D003932:Heroin / Q000008:administration & dosage* / Q000009:adverse effects; D006801:Humans; D010149:Postoperative Pain / Q000517:prevention & control; D011183:Postoperative Complications / Q000139:chemically induced; D020250:Postoperative Nausea and Vomiting / Q000139:chemically induced; D011247:Pregnancy; D011446:Prospective Studies; D011537:Pruritus / Q000139:chemically induced
D000701:Analgesics, Opioid; D015760:Alfentanil; D003932:Heroin