Anesth Analg 2004;99:584-588
© 2004 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000122823.50592.C9
REGIONAL ANESTHESIA
Nerve Stimulator-Assisted Evoked Motor Response Predicts the Latency and Success of a Single-Injection Sciatic Block
Radha Sukhani, MD,
Antoun Nader, MD,
Kenneth D. Candido, MD,
Robert Doty, Jr., MD,
Honorio T. Benzon, MD,
Edward Yaghmour, MD,
Mark Kendall, MD, and
Robert McCarthy, PharmD
Department of Anesthesiology, Northwestern University/Feinberg School of Medicine, Chicago, IL
Address correspondence and reprint requests to Radha Sukhani, MD, Department of Anesthesiology, 251 E. Huron St., F5-704, Chicago, IL 60611. Address e-mail to radhasukhani{at}yahoo.com
Variable onset latency of single-injection sciatic nerve block (SNB) may result from drug deposition insufficiently close to all components of the nerve. We hypothesized that this variability is caused by the needle tip position relative to neural components, which is objectified by the type of evoked motor response (EMR) elicited before local anesthetic injection. One-hundred ASA I–II patients undergoing reconstructive ankle surgery received infragluteal-parabiceps SNB using 0.4 mL/kg (maximum 35 mL) of levobupivacaine 0.625%. The end-point for injection was the first elicited EMR: inversion (I), plantar flexion (PF), dorsiflexion (DF), or eversion (E) at 0.2–0.4 mA. The frequencies of the EMRs were: I 40%, PF 43%, E 14%, and DF 3%. SNB was considered complete if both tibial and common peroneal nerves were blocked and failed if either analgesia to pinprick was not observed at 30 min or anesthesia at 60 min. Patients with an EMR of I demonstrated shorter mean times (±95% confidence interval [CI]) to complete the block with 8.5 (95% CI, 6.2–10.8) min compared to 27.0 (95% CI, 20.6–33.4) min after PF (P < 0.001) and 30.4 (95% CI, 24.9–35.8) min after E (P < 0.001). No rescue blocks were required in group I compared with 24% (P = 0.001) and 71% (P < 0.001) of patients in groups PF and E, respectively. We conclude that EMR type during nerve stimulator-assisted single-injection SNB predicts latency and success of complete SNB because the observed EMR is related to the positioning of the needle tip relative to the tibial and common peroneal nerves.
IMPLICATIONS: The type of evoked motor response (EMR) during nerve stimulator-assisted single-injection sciatic nerve block impacts the latency and success of complete block. Compared with EMRs plantar flexion, dorsiflexion, or eversion, EMR inversion is associated with the shortest latency to a complete block of the sciatic nerve.
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