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

BACKGROUND Co-administration of small doses of opioids and bupivacaine for spinal anaesthesia reduces intraoperative discomfort and may reduce postoperative analgesic requirements in patients undergoing Caesarean section. Fentanyl and diamorphine are the two most frequently used agents in UK obstetric anaesthetic practice. METHODS Seventy-five healthy parturients scheduled for elective Caesarean section under spinal anaesthesia using hyperbaric 0.5% bupivacaine, were randomly allocated to additionally receive intrathecal fentanyl 20 micrograms, diamorphine 300 micrograms or 0.9% saline. Patients also received i.v. cyclizine and rectal diclofenac. RESULTS Less supplementary intraoperative analgesia was required by 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 significantly lower if diamorphine was administered (31 (21) mg), in comparison with the other two groups (control 68 (26) mg; fentanyl 62 (26) mg) (P < 0.05). Reduced visual analogue pain scores were evident 12 h following diamorphine, but observed only for 1 h after fentanyl when compared with the control (P < 0.05). Mild pruritus was more common for 2 h after either spinal opioid (P < 0.05), but no inter-group differences were observed for the remainder of the first 24 h. Patients displayed deeper levels of sedation both acutely and 12 h after administration of intrathecal fentanyl (P < 0.05). CONCLUSIONS Both intrathecal opioids reduce intraoperative discomfort, but only diamorphine reduced postoperative analgesic requirement beyond the immediate postoperative period.