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REGIONAL ANESTHESIA

The Effects of Single or Multiple Injections on the Volume of 0.5% Ropivacaine Required for Femoral Nerve Blockade

University of Milan, Department of Anesthesiology, IRCCS H. San Raffaele, Milan, Italy

Address correspondence to Dr. A. Casati, Department of Anesthesiology, IRCCS H. San Raffaele, Via Olgettina 60, 20132 Milan, Italy. Address e-mail to casati.andrea{at}hsr.it

We compared the effects of using a single- or multiple-injection technique on the volume of 0.5% ropivacaine required to block the femoral nerve, in a prospective, randomized, blinded fashion in which 50 premedicated patients received a femoral nerve block with 0.5% ropivacaine by use of a nerve stimulator and either a single- (n = 25) or multiple- (n = 25) injection technique. Muscular twitches were elicited at 0.5 mA before anesthetic injection. The designated volume of local anesthetic was equally divided among contraction of the vastus medialis, vastus intermedius, and vastus lateralis for the multiple injections, or it was injected at the contraction of the vastus intermedius with motion of the patella for the single injection. The local anesthetic volumes were varied for consecutive patients by using an up-and-down staircase method; a blinded observer determined the adequacy of nerve blockade (loss of pinprick sensation in the medial, patellar, and lateral portions of the knee, with concomitant block of the quadriceps muscle) 20 min after injection. The mean (95% confidence interval) volume required for blocking the femoral nerve with the multiple-injection technique (14 [12–16] mL) was significantly smaller than that observed with the single injection (23 [20–26] mL) (P = 0.001). According to logistic regression analyses, the 95% effective volumes of ropivacaine required to block the femoral nerve within 20 min after injection were 29 and 21 mL with a single or multiple injection, respectively. We conclude that searching for multiple muscular twitches reduces the volume of 0.5% ropivacaine required to produce blockade of the femoral nerve.

Implications: We evaluated the effects of using a single- or multiple-injection technique onthe volume of 0.5% ropivacaine required to block the femoral nerve. The 95%effective concentration values for producing the same degree of sensory andmotor blockade of the femoral nerve within 20 min after injection were 29 mLafter elicitation of a patella twitch and 21 mL when the three main branchesof the femoral nerve were identified, potentially leading to an importantbenefit for patients receiving peripheral nerve blocks.

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