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

To the Editor: We have some concerns regarding the methodology of the Casati et al. (1) study. At the level of the inguinal ligament, the femoral nerve splits into its three main branches, which then separate at the level of the inguinal crease (2). We agree with the authors that the multiple injection technique at this level permits to localize and successfully block each branch separately with a constant volume of local anesthetics. In our opinion, however, the minimum volume needed to block the femoral nerve and its main branches will depend on the exact positioning of the tip of the needle, which can elicit the same motor response despite being placed either slightly median or lateral of the nerve. Even with a standardized technique as used in this study (localization of the middle branch: vastus intermedius nerve), we believe that the position of the needle may vary from the theoretical midpoint of the three nerves, which may influence the spread of the injected local anesthetics and consequently the quality as well as the onset time of the block. To minimize this anatomical bias in the single injection group, we believe that instead of blocking the femoral nerve at the level of the inguinal crease, it should be blocked just below the inguinal ligament where the three branches are close to each other. Even at this level there may be a variation of the needle position using the same stimulating technique, but this may not have the same consequences on the quality of the nerve block. To indisputably demonstrate the advantages of the multiple injection technique, the authors should have included in their study a third group receiving the single shot just below the inguinal ligament. Georgios Ekatodramis, MD John M. Bonvini, MD Alain Borgeat, IVID