This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Google Scholar Articles by Danelli, G. Articles by Fanelli, G. PubMed PubMed Citation Articles by Danelli, G. Articles by Fanelli, G. Related Collections Mechanisms Anesthetic Techniques Regional Anesthesia Pharmacology

---

ANALGESIA

The Effects of Ultrasound Guidance and Neurostimulation on the Minimum Effective Anesthetic Volume of Mepivacaine 1.5% Required to Block the Sciatic Nerve Using the Subgluteal Approach

From the Department of Anesthesiology, Intensive Care and Pain Therapy, University Hospital, Parma, Italy.

Address correspondence and reprint requests to Giorgio Danelli, MD, Department of Anesthesia, Intensive Care and Pain Therapy, University Hospital of Parma, Viale Gramsci 14, 43100 Parma, PR, Italy. Address e-mail to gdanelli{at}ao.pr.it.

Abstract

BACKGROUND: We tested the hypothesis that ultrasound (US) guidance may reduce the minimum effective anesthetic volume (MEAV₅₀) of 1.5% mepivacaine required to block the sciatic nerve with a subgluteal approach compared with neurostimulation (NS).

METHODS: After premedication and single-injection femoral nerve block, 60 patients undergoing knee arthroscopy were randomly allocated to receive a sciatic nerve block with either NS (n = 30) or US (n = 30). In the US group, the sciatic nerve was localized between the ischial tuberosity and the greater trochanter. In the NS group, the appropriate muscular response (foot plantar flexion or inversion) was elicited (1.5 mA, 2 Hz, 0.1 ms) and maintained to 0.5 mA. The volume of the injected local anesthetic was varied for consecutive patients based on an up-and-down method, according to the response of the previous patient. The initial volume was 12 mL. An independent observer evaluated the occurrence of complete loss of pinprick sensation and motor block: positive or negative responses within 20 min after the injection determined a 2-mL decrease or increase for the next patient, respectively.

RESULTS: The mean MEAV₅₀ for sciatic nerve block was 12 mL (95% confidence interval [CI], 10–23 mL) in Group US and 19 mL (95% CI, 15–23 mL) in Group NS (P < 0.001). The effective dose in 95% of cases was 14 mL (95% CI, 12–17 mL) in Group US and 29 mL (95% CI, 25–40 mL) in Group NS (P = 0.008).

CONCLUSIONS: US provided a 37% reduction in the MEAV₅₀ of 1.5% mepivacaine required to block the sciatic nerve compared with NS.