Effects of intrathecal and i.v. small-dose sufentanil on the median effective dose of intrathecal bupivacaine for Caesarean section

Background Spinal anaesthesia with bupivacaine combined with sufentanil has been widely used for Caesarean section. However, the main site of action (spinal vs central) of intrathecal (IT) sufentanil is controversial. The aim of this study was to examine the predominant mechanism of action of IT, small-dose sufentanil when added to bupivacaine for Caesarean section, by comparing the effects of IT and i.v. sufentanil 2.5 µg on the median effective dose (ED 50 ) of bupivacaine. Methods Ninety parturients undergoing elective Caesarean section with a combined spinal–epidural technique were enrolled into this prospective, double-blind, up-down sequential allocation study. According to the up-down sequential allocation, parturients received varying doses of bupivacaine alone (C group) or co-administered with i.v. sufentanil 2.5 µg group (IVS group; n = 30) or IT sufentanil 2.5 µg group (ITS group; n = 30). The possible maternal or neonatal adverse effects were also recorded. Results The ED 50 of bupivacaine was 6.3 mg (95% CI 6.2–6.5) in the C group, 5.2 mg (95% CI 5.1–5.4) in the IVS group, and 3.0 mg (95% CI 2.9–3.1) in the ITS group. The ED 50 in the ITS group was significantly lower as compared with the other two groups ( P P = 0.011, compared with the other two groups), no significant differences among groups were observed regarding the frequencies of the maternal or neonatal adverse effects. Conclusions Compared with an equal dose of sufentanil i.v., intrathecally administered sufentanil 2.5 µg has a significant local anaesthetic‐sparing effect via a predominantly spinal mechanism for Caesarean section.