Background and Objectives: The aim of this study was to compare the anesthetic and analgesic characteristics of the administration of an initial bolus of 20, 30, or 40 mL of ropivacaine 0.5% through a lateral popliteal sciatic catheter.

Methods: Sixty patients scheduled for foot surgery under continuous sciatic lateral popliteal nerve block were included in this double-blinded study. Patients were randomly assigned to 1 of 3 groups: 20 mL, 30 mL, or 40 mL of ropivacaine 0.5%. Time to obtain a complete sensory block and duration of analgesia were recorded. Failure of the continuous block and complications such as technical or neurologic problems were noted.

Results: Data are presented as mean ± SD, median and ranges, or percent of patients and were compared by application of analysis of variance or Kruskal-Wallis when required. Time to complete sensory block (31 [10-70] v 25 [5-50] v 25 [5-40] min), percentage of failure (5% v 5% v 0%), and duration of action (995 [278-1,800] v 967 [420-2,175] v 915 [190-1,900] min) were not statistically different between 20 mL, 30 mL, and 40 mL ropivacaine 0.5% groups, respectively. No complications were noted.

Conclusions: This dose-response study shows that 20 mL of ropivacaine 0.5% injected through an indwelling lateral popliteal catheter is the optimal dose for foot surgery. Higher doses of 30 mL or 40 mL did not provide any further advantage.