BACKGROUND: Comparing relative potency of
new local anesthetics, such as levobupivacaine and ropivacaine, by the
minimum local analgesic
concentration model has not been described for
caudal anesthesia. Therefore, we performed a prospective, randomized,
double-blind
study to determine the minimum local analgesic
concentrations of a caudal single shot of ropivacaine and
levobupivacaine in
children and to describe the upper dose-response
curve.
METHODS: We performed a
two-stage prospective, randomized, double-blind study comparing the
dose-response curves of caudal ropivacaine
and levobupivacaine in children. In phase 1, 80
boys were randomized to receive either ropivacaine or levobupivacaine.
In
the second phase a further 32 patients were
randomly allocated to receive caudal anesthesia with doses designed to
delineate
the upper dose-response range (the 50% effective
dose [ED50]-ED95 range).
RESULTS: There were no significant differences in ED50 values for caudal ropivacaine and levobupivacaine. The ED50 for levobupivacaine estimated from the Dixon Massey method was 0.069% (95% CI 0.056%-0.082%) and for ropivacaine was 0.075%
(95% CI 0.058%-0.092%). Estimated by isotonic regression the ED50 and ED95 respectively of levobupivacaine were 0.068 (0.04-0.09) and 0.20% (95% CI 0.16%-0.24%). For ropivacaine ED 50 and ED95 were
0.066 (0.033-0.098) and 0.225% (95% CI 0.21%-0.24%).
CONCLUSIONS: In children receiving one minimum alveolar anesthetic concentration of sevoflurane, there were no significant differences
in the ED50 for caudal levobupivacaine and ropivacaine. The potency ratio at ED50 was 0.92 and 0.89 at ED95, indicating that caudal levobupivacaine and ropivacaine have a similar potency.
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