Letters to the Editor: Letters & Announcements
To the Editor:
The most significant result of the study by Ilfeld et al.1 on continuous infraclavicular blockade was that the effect of varying local anesthetic dose and concentration was completely opposite to that observed in their earlier study of continuous popliteal blockade.2 We agree that this difference is likely to be due to the anatomical differences between the two sites. The sciatic nerve is a compact single structure, and a smaller volume of local anesthetic is therefore more likely to distribute to all areas of the nerve. In contrast, the brachial plexus in the infraclavicular region is composed of three separate cords spread out and separated by the axillary artery and, therefore, less likely to be uniformly blocked by local anesthetic. Our experience supports this; we find that it is difficult to maintain postoperative sensory loss in all terminal nerve distributions with a continuous infraclavicular catheter.
It would have been useful to know the distribution of sensory loss and its correlation with the site of surgical pain. The paradoxical association of a greater incidence of an insensate limb (defined as “any part of their surgical extremity”) with less postoperative analgesia in the 0.4% ropivacaine group may be explained if the part of the lower arm that was insensate was not also the site of surgical pain. It is also possible that patients in this group self-administered more boluses of local anesthetic in an attempt to improve analgesia and, hence, received a larger mass and volume of local anesthetic. Unfortunately, the absence of data on the number of boluses that patients actually received precludes us interpreting the relative contribution of local anesthetic concentration, mass, and volume to sensory block and analgesic quality.
The location of the catheter tip may also determine the quality of continuous infraclavicular blockade. The authors did not specify if the motor response used as the end point for catheter placement was random, standardized, or matched to the site of surgery. If the catheter tip is placed closest to the cord supplying the distribution of surgical pain, it is possible that infusion of a smaller volume of more concentrated local anesthetic will produce dense sensory block at the site of surgery, while sparing other parts of the upper limb. If surgery is in the distribution of two or more cords, or if the tip is not optimally located, then we may expect that a larger volume (of infusion and bolus) will be required for good analgesia. Some studies3–5 suggest that the optimal end point for a single-shot infraclavicular block is a motor response in the radial distribution, because this is most likely to be associated with circumferential spread around all three cords. There are no data, however, on whether this is applicable to continuous infraclavicular block.
Finally, we believe that designing the appropriate dosing regimen also requires consideration of the postoperative clinical goals in individual patients. These goals can range from dense motor blockade to facilitate continuous passive motion (e.g., in total elbow replacement) to mild sensory analgesia to facilitate early active physical therapy (e.g., total knee replacement). The recipe for optimal postoperative continuous peripheral nerve block is therefore unlikely to be either simple or universal.
Ki Jinn Chin, FANZCA, FRCPC
Anahi Perlas, FRCPC
Vincent Chan, FRCPC
Richard Brull, FRCPC
Department of Anesthesia
Toronto Western Hospital
Toronto, Ontario, Canada
1.Ilfeld BM, Le LT, Ramjohn J, Loland VJ, Wadhwa AN, Gerancher JC, Renehan EM, Sessler DI, Shuster JJ, Theriaque DW, Maldonado RC, Mariano ER, Horlocker TT. The effects of local anesthetic concentration and dose on continuous infraclavicular nerve blocks: a multicenter, randomized, observer-masked, controlled study. Anesth Analg 2009;108:345–50
2.Ilfeld BM, Loland VJ, Gerancher JC, Wadhwa AN, Renehan EM, Sessler DI, Shuster JJ, Theriaque DW, Maldonado RC, Mariano ER. The effects of varying local anesthetic concentration and volume on continuous popliteal sciatic nerve blocks: a dual-center, randomized, controlled study. Anesth Analg 2008;107: 701–7
3.Bloc S, Garnier T, Komly B, Asfazadourian H, Leclerc P, Mercadal L, Morel B, Dhonneur G. Spread of injectate associated with radial or median nerve-type motor response during infraclavicular brachial-plexus block: an ultrasound evaluation. Reg Anesth Pain Med 2007;32:130–5
4.Bloc S, Garnier T, Komly B, Leclerc P, Mercadal L, Morel B, Dhonneur G. Single-stimulation, low-volume infraclavicular plexus block: influence of the evoked distal motor response on success rate. Reg Anesth Pain Med 2006;31:433–7
5.Minville V, Fourcade O, Bourdet B, Doherty M, Chassery C, Pourrut JC, Gris C, Eychennes B, Colombani A, Samii K, Bouaziz H. The optimal motor response for infraclavicular brachial plexus block. Anesth Analg 2007;104:448–51