In Reply:--We would like to thank Sander for his letter regarding an important (and still not widely understood) topic, the use of electromyography in clinical anesthesia. We wholeheartedly agree with his perception of the "lack of communication between medical specialties."
Although some of the information in our article may have appeared previously in the textbooks of electromyography cited by Sander, the paucity of original investigations published in the anesthesia (or neurology) literature with regard to the effect of electrode polarity on the evoked response was evident.
With regard to the stimulus intensity required to elicit a supramaximal response, the classic anesthesia teaching is to determine the maximal evoked response for each patient by progressively increasing the stimulus intensity and then increasing it further by 20-30% to ensure "supramaximal stimulation." However, contrary to our findings, the understanding had been that, in general, currents much less than 100 mA were sufficient. This contention was supported by the fact that the vast majority of the clinically available nerve stimulators have maximal current outputs of only 60-70 mA. Furthermore, only a couple of the newer nerve stimulators have the ability to vary the stimulus pulse duration, and only between 0.2 and 0.3 ms.
In conclusion, we are encouraged by the fact that a nonanesthesiologist has taken interest in our literature and that our findings are supported by an expert electromyographer; we are indebted to Sander for his correct call to increase information exchange among medical fields.
Sorin J. Brull, MD, David G. Silverman, MD, Department of Anesthesiology, Yale University School of Medicine, New Haven, Connecticut 06520-8051.
