Comparison of intrathecal fentanyl and diamorphine in addition to bupivacaine for caesarean section under spinal anaesthesia

Background. Co-administration of small doses of opioids andbupivacaine for spinal anaesthesia reduces intraoperative discomfortand may reduce postoperative analgesic requirements in patientsundergoing Caesarean section. Fentanyl and diamorphine are thetwo most frequently used agents in UK obstetric anaestheticpractice. Methods. Seventy-five healthy parturients scheduled for electiveCaesarean section under spinal anaesthesia using hyperbaric0.5% bupivacaine, were randomly allocated to additionally receiveintrathecal fentanyl 20 µg, diamorphine 300 µg or0.9% saline. Patients also received i.v. cyclizine and rectaldiclofenac. Results. Less supplementary intraoperative analgesia was requiredby patients in either opioid group (4%) compared with the control(32%) (P<0.05). Twenty four hours after spinal injection,total mean (SD) postoperative morphine requirement was significantlylower if diamorphine was administered (31 (21) mg), in comparisonwith the other two groups (control 68 (26) mg; fentanyl 62 (26)mg) (P<0.05). Reduced visual analogue pain scores were evident12 h following diamorphine, but observed only for 1 h afterfentanyl when compared with the control (P<0.05). Mild pruritiswas more common for 2 h after either spinal opioid (P<0.05),but no inter-group differences were observed for the remainderof the first 24 h. Patients displayed deeper levels of sedationboth acutely and 12 h after administration of intrathecal fentanyl(P<0.05). Conclusions. Both intrathecal opioids reduce intraoperativediscomfort, but only diamorphine reduced postoperative analgesicrequirement beyond the immediate postoperative period. Br J Anaesth 2002; 89: 452–8