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Department of Anesthesia, Balgrist University Hospital, Zurich, Switzerland
To the Editor:
We congratulate Iskandar et al. for performing this study with the interesting topic of the analgesic effect of clonidine applied in the interscalene space (1). The results of this study are important, since they completely disagree with those found by Sia et al. (2). With respect to known literature (2,3) and the methods described by the authors, the presented results may raise concern. The scientific description of the chosen approach to the interscalene space and a detailed explanation of the catheter insertion procedure have not been described. It would be of great interest to have more data about the nerve stimulator settings (milliseconds, hertz), other than just that the output had to be lower than 0.7 mA. Very important information is also lacking about how far the catheter was threaded past the tip of the needle. All these points lead directly to our main concern: there is in this study no validation of the correct placement of the catheter before commencement of surgery. This would have been easily performed with a short acting local anesthetic bolus. Without this, we can only speculate whether the catheter was placed correctly or not, and therefore, we do not really know whether the drug given through the catheter may have any effect at all on the nerves, making the validity of the results doubtful. Another point to mention is the imprecise description of the authors’ management of remifentanil at the end of surgery. The timing and mode in which remifentanil is stopped on completion of surgery is very important for the postoperative pain setting, since its rapid discontinuation produces a hyperalgesic state (4). Concerning the statistics, post hoc tests for correction of repeated measurements are lacking, as well as a power analysis.
References
Clinique Chirurgicale Bordeaux-Mérignac, Mérignac, France
In Response:
We thank Blumenthal et al. for their attention to our study examining the analgesic effect of interscalene block using clonidine as an analgesic for shoulder arthroscopy. We would like to respond to several points raised by Dr. Blumenthal.
First, the interscalene catheter was placed by an experienced anesthesiologist, with nerve stimulator help (Stimuplex Braun). The stimulation frequency was set as 2 Hz, while the duration of stimulation was set as 0.2 ms. The intensity of stimulating current, initially set to deliver 2 mA, was gradually decreased to 
0.7 mA after the appropriate muscular response was observed. Then the catheter was advanced and secured with a transparent occlusive dressing. Although there is no validation in this study of the correct placement of the catheter before commencement of surgery, all catheters were effective for postoperative analgesia, indicating their correct placements.
Second, the continuous administration of remifentanil during general anesthesia was stopped at the end of surgery in all patients (before arrival to the PACU), thus this drug does not influence postoperative analgesia.
We believe that clonidine applied alone to the interscalene plexus enhanced postoperative analgesia after shoulder arthroscopy.
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