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Background: We carried out this prospective, randomized, double-blind study in order to evaluate whether the intrathecal addition of sufentanil 3.3 mcg affects both the minimum local anaesthetic dose (MLAD) of spinal levobupivacaine and ropivacaine for a caesarean section and enhances the spinal block characteristics. Methods: One hundred and eighty women were randomly allocated into four groups: levobupivacaine (Group L), levobupivacaine plus sufentanil (Group L+S), ropivacaine (Group R) and ropivacaine plus sufentanil (Group R+S). Each received 3 ml of the study solution intrathecally as part of a combined spinal/epidural technique. The initial dose was 12 mg for Groups L and L+S, and 15 mg for Groups R and R+S. The test solution was required to achieve a visual analogue pain score (VAPS) of 30 mm or less to be considered effective at skin incision, uterine incision, birth, peritoneal closure and at the conclusion of surgery. Effective or ineffective responses determined a 0.5 mg decrease or increase of the same drug, respectively, for the next patient in the same group, using an up–down sequential allocation. Results: Using the Dixon and Massey formula, the MLAD was 10.65 mg [confidence interval (CI) 95%: 10.14–11.56] in Group L, 4.73 mg (CI 95%: 4.39–5.07) in Group L+S, 14.12 mg (CI 95%: 13.50–14.60) in Group R and 6.44 mg (CI 95%: 5.86–7.02) in Group R+S. Conclusions: The addition of sufentanil reduced the MLAD of both the local anaesthetics. It did not affect their potency ratio significantly and resulted in enhanced spinal anaesthesia.

We determined the minimum local anaesthetic dose (MLAD) of spinal levobupivacaine and ropivacaine for Caesarean section. Ninety women were randomly allocated to two groups and received 3 ml of study solution by a combined spinal/epidural technique. The initial dose was 12 mg for levobupivacaine and 17 mg for ropivacaine groups. To be considered effective, a test solution had to achieve a visual analogue pain score (VAPS) of 30 mm or less at skin incision, uterine incision, birth, peritoneal closure, and at the end of surgery. Effective or ineffective responses determined, respectively, a 0.3 mg decrease or increase of the same drug for the next patient in the same group, using up-down sequential allocation. The MLAD of levobupivacaine was 10.58 mg (CI 95\%: 10.08-11.09) and the MLAD of ropivacaine 14.22 mg (CI 95\%: 13.67-14.77), using the Dixon and Massey formula. The potency ratio between spinal levobupivacaine and spinal ropivacaine was 1.34.