Minimum local anaesthetic dose (MLAD) of intrathecal levobupivacaine and ropivacaine for Caesarean section*

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Abstract
Summary: 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.