Letters to the Editor: Letters & Announcements
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.
Stephan Blumenthal, MD
Marco Nadig, MD
Alain Borgeat, MD
Department of Anesthesiology
Orthopedic University Clinic Balgrist
1. 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.
2. 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.
3. 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.