Anesth Analg 2004;99:1874-1875
© 2004 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000138548.73265.EE
LETTERS TO THE EDITOR
The Supraclavicular Block with a Nerve Stimulator: Where Is the Needle Tip, That Is the Question
Stephan Blumenthal, MD,
Marco Nadig, MD, and
Alain Borgeat, MD
Department of Anesthesiology, Orthopedic University Clinic Balgrist, Zurich, Switzerland, aborgeat@balgrist.unizh.ch
To the Editor:
We congratulate Franco et al. for performing this interesting study (1), comparing the quality of supraclavicular block with different current outputs of the nerve stimulator, before the drug was injected. The results of their study are intriguing, since they disagree with those found by other investigators (2,3). However, the important question raised by this study cannot be adequately answered by the results of this investigation. The results of this trial are blunted, since it is impossible to know (or to guess) what would have been the minimum current still able to elicit a motor response, which would have indirectly demonstrated how close to the cord the tip of the needle was. As experienced performers of the supraclavicular block, Franco et al. initially might have placed the stimulating needle very close to one cord, which is underlined by their statement that "it is possible that some or all of the twitches elicited at 0.9 mA could have still been present at 0.5 mA." The authors cannot rule out that the tip of the needle in the 0.9 mA group would have been closer to the cord than in the 0.5 mA group. Without comparing the parallel between the reduction of the current and the motor response until the minimum current was found, no valid conclusion can be drawn. The conclusion of their study can lead less experienced colleagues to inject the local anesthetic too far from the nerves with consequently a high block failure rate. When dealing with output currents of nerve stimulator and needle tip-nerve distance, it is mandatory to mention the stimulus duration (2,3). Describing the relationship between current intensity needed to produce a motor twitch and the needle tip-nerve distance, the authors mentioned an "inverse proportion," which probably is a spelling error, since it is a proportional relation.
References
- Franco CD, Domashevich V, Voronov G, et al. The supraclavicular block with a nerve stimulator: to decrease or not to decrease, that is the question. Anesth Analg 2004; 98: 1167–71.[Abstract/Free Full Text]
- Hadzic A, Vloka J, Hadzic N, et al. Nerve stimulators used for peripheral nerve blocks vary in their electrical characteristics. Anesthesiology 2003; 98: 969–74.[Web of Science][Medline]
- Neuburger M, Rotzinger M, Kaiser H. Electric nerve stimulation in relation to impulse strength: a quantitative study of the distance of the electrode point to the nerve [in German]. Anaesthesist 2001; 50: 181–6.[Medline]
Response
Carlo D. Franco, MD
Department of Anesthesiology and Pain Management, John H. Stroger Jr. Hospital of Cook County, Chicago, IL, carlofra@aol.com
In Response:
We appreciate this letter for it gives us an opportunity to clarify the goals and results of our study.
Our work simply intended to determine whether a supraclavicular block could be injected at the initial "seeking current" without having a negative impact on success rate. As we mentioned in our study, it was not our intention to compare 0.9 mA with 0.5 mA as "minimum stimulating currents." That work, interesting as it might be, has not been performed yet.
The authors think that our results are "intriguing since they disagree with those found by other investigators," giving two references to back such a statement. However, those two papers never investigated whether a supraclavicular block, or any other block for that matter, can or cannot be injected at a higher current than other techniques.
It has never been our practice to determine the current at which our elicited response disappears. Instead, we are content that for most of our techniques, our sought response is still present at 0.5 mA. One of the exceptions is the supraclavicular block that we now inject routinely at around 0.85 mA, the same current at which we initiate it. When we used to inject the supraclavicular block at 0.5 mA, we did not know exactly where the tip of the needle was at the moment of injection nor do we know it now when we inject it at a higher current. To avoid intraneural injection we still rely on light sedation, small injection pressure, and meticulous technique. As we also mentioned in our study, we do not advocate raising the output at which the injection is initiated with any other technique, at least not at the present time.
We argue that single injection plexus anesthesia (the anesthesia of more than one nerve by a single injectate) involves more than just proximity to a nerve structure, but also the identification of a point from where the solution is able to evenly reach the plexus. We believe that every plexus technique has such a point from where the spread is more satisfactory. Our experience with the supraclavicular block clearly demonstrates that an injection performed in front of the lower trunk at 0.9 mA is definitely better than a similar injection performed in front of the upper trunk at 0.5 mA. Having now performed close to 1,000 supraclavicular blocks injected immediately after finding a response from the lower trunk has convinced us that this is a safe and practical approach that saves time and needle manipulations, and, from our perspective, this is the main value of our work.
In terms of stimulus duration, it is known that the Stimuplex DIG provides a fixed pulse width of 0.1 ms. A short pulse like this is considered the most suitable for nerve localization, and the clinical utility of changing the pulse width is not yet well defined (1).
The magnitude of the response is indeed inversely proportional to the needle tip-nerve distance, thus there is not a "spelling error" as suggested.
Finally, we believe that the techniques of regional anesthesia performed with a nerve stimulator are still evolving, and those who practice them are still discovering the specifics that differentiate one technique from another.
Reference
- Hadzic A. Peripheral nerve stimulators and nerve stimulation. In: Hadzic A, Vloka JD, eds. Peripheral nerve blocks principles and practice. New York: McGraw-Hill, 2004: 43–49.
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