What Is the Minimum Effective Volume of Local Anesthetic Required for Sciatic Nerve Blockade? A Prospective, Randomized Comparison Between a Popliteal and a Subgluteal Approach

Abstract

For sciatic nerve blockade, no study has defined the optimal volume of local anesthetic required to block the nerve. The current, prospective, randomized investigation was designed to find a minimum volume of 1.5% mepivacaine required to block the sciatic nerve using the subgluteal and posterior popliteal approaches. A total of 56 patients undergoing foot surgery were randomly assigned to receive sciatic nerve block by means of a posterior subgluteal (group subgluteal, n = 28) or a posterior popliteal (group popliteal, n = 28) approaches. All blocks were performed with the use a nerve stimulator (stimulating frequency, 2 Hz, intensity 1.5-0.5 mA) and a perineural stimulating catheter. In all patients, plantar flexion of the foot was elicited at <0.5 mA, to maintain consistency among groups. The volume of local anesthetic used in each patient was based on the modified Dixon's up-and-down method. Complete anesthesia was defined as complete loss of pinprick sensation in the sciatic nerve distribution with concomitant inability to perform plantar or dorsal flexion of the foot 20 min after injection. The mean volume of local anesthetic required to block the sciatic nerve was 12 +/- 3 mL in the subgluteal group and 20 +/- 3 mL in the popliteal group (P < 0.05). The ED95 for adequate block of the sciatic nerve was 17 mL in the subgluteal group and 30 mL in the popliteal group. The authors conclude that a larger volume of local anesthetic is necessary to block the sciatic nerve at a more distal site (popliteal approach) as compared with a more proximal level (subgluteal approach).

A Randomized Comparison of a Modified Intertendinous and Classic Posterior Approach to Popliteal Sciatic Nerve Block

“…[5][6][7] The difference in latency may reflect injection within a common perineural sheath, as well as the increasing width of the perineural space at distal sites. [7][8][9] Other studies have described block sites similar to those used in this study. Borgeat et al described a posterior block site at the apex popliteal fossa 9 cm above the popliteal crease.…”

Popliteal Sciatic Nerve Block in a Pregnant Patient in the Last Trimester

“…Because of the lower foetal protein binding capacity than the mother, the foetus cannot control the blood levels of the drugs efficiently and potential toxic reactions may occur (2). Therefore, because of the necessity of using almost all the drugs at a minimum effective dose in pregnant patients (14), we have currently used 30 mL of 0.375% levobupivacaine, which is the minimal effective volume for the blockade of the sciatic nerve in the popliteal region as described (15). Although that dose was less than the clinically recommended doses of 2-3 mg kg −1 , we achieved adequately satisfactory anaesthesia without side effects.…”

Ultrasound-guided proximal and distal sciatic nerve blocks in children

“…It forms an excellent mirror to help identify the sciatic nerve by ultrasound, the hypoechoic muscles contrasting with the hyperechoic nerve [7]. The muscles envelop the sciatic nerve; therefore, a lower dose of local anesthetic may be used to block the proximal sciatic nerve compared with the distal popliteal approach [8]. However, a lower dose of local anesthetic was not used to embed the sciatic nerve in the subgluteal compared with the popliteal region.…”