Modelling of the optimal bupivacaine dose for spinal anaesthesia in ambulatory surgery based on data from systematic review

BACKGROUND: Spinal bupivacaine is used for day-case surgery but the appropriate dose that guarantees hospital discharge is unknown. OBJECTIVE: We sought to determine the spinal bupivacaine dose that prevents delayed hospital discharge in ambulatory surgery. DESIGN: Systematic review of clinical trials. DATA SOURCES: Comprehensive search in electronic databases of studies published between 1996 and 2014 reporting the use of spinal bupivacaine in ambulatory patients. Additional articles were retrieved through hyperlinks and by manually searching reference lists in original articles, review articles and correspondence published in English and French. MAIN OUTCOME MEASURES: Data were used to calculate, motor block duration and discharge time, an estimated maximal effect (Emax: maximum theoretical time of motor block) and the effective dose to obtain half of Emax (D50) with 95% confidence intervals (CIs). A simulation was performed to determine the dose corresponding to a time to recovery of 300 min for motor function, and 360 min for discharge, in 95% of the patients. RESULTS: In total, 23 studies (1062 patients) were included for analysis of the time to recovery of motor function, and 12 studies (618 patients) for the time to hospital discharge. The Emax for recovery of motor function was 268 min [95% CI (189 to 433 min)] and the D50 was 3.9 mg [95% CI (2.3 to 6.2 mg)]. A 7.5-mg dose of bupivacaine enables resolution of motor block and ambulation within 300 min in 95% of the patients. A 5-mg dose or less was associated with an unacceptable failure rate. CONCLUSION: Ambulatory surgery is possible under spinal anaesthesia with bupivacaine although the dose range that ensures reliable anaesthesia with duration short enough to guarantee ambulatory management is narrow.

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