Anesth Analg 2002;95:254
© 2002 International Anesthesia Research Society
LETTERS TO THE EDITOR
What to Do with Clonidine with Long-Acting Local Anesthetic in Brachial Plexus Block?
Marco Nadig, MD,
Georgios Ekatodramis, MD, and
Alain Borgeat, MD
Department of Anesthesia, Orthopedic University Clinic of Zurich/Balgrist, University Clinic of Zurich/Balgrist, Zurich, Switzerland
To the Editor: We read with great interest the article of Culebras et al. (1). Although we agree with some of the conclusions made by the authors, we have some concerns dealing with the methodology of the study.
First, we would like to know which type of nerve stimulator was used. More information about the settings of the neurostimulator, especially the exact impulse duration, is needed in the context of a manuscript dealing with regional anesthesia. Also, why did the authors use a solution of 40 mL of 0.5% bupivacaine with epinephrine (1/200000)? We believe that the effect of clonidine could have been masked by the presence of epinephrine, therefore creating a bias. In our opinion the use of a solution without epinephrine would have been more appropriate to demonstrate whether clonidine prolongs the effects of bupivacaine in this setting.
Hemodynamic changes resulting from clonidine are not surprising. However, in the present study hemodynamic measurements (Figs. 2 and 3) are difficult to evaluate, as they were made after isoflurane had been given. Is it really an effect of clonidine or is it the result of a supraadditive interaction between the two drugs? An awake patient would have provided more informative results.
The satisfaction score as described in the methods section was assessed at 24 h and 48 h after the end of the study. But in the results section the authors only mentioned a satisfaction score at 48 h. What about after 24 h? Is it allowed to ask a satisfaction score twice at 24 h interval? Finally, we believe the statistics used are not appropriate. Evaluation of the pain score (continuous variable) should have been analyzed by a nonparametric test (nonnormal distribution) with an ad hoc test to correct for repeated measurements.
References
- Culebras X, Van Gessel E, Hoffmeyer P, Gamulin Z. Clonidine combined with a long anesthetic does not prolong postoperative analgesia after brachial plexus block but does induce hemodynamic changes. Anesth Analg 2001; 92: 199–204.[Abstract/Free Full Text]
Response
Xavier Culebras, MD, and
Zdravko Gamulin, MD
Division of Anesthesiology, Geneva University Hospitals, Geneva, Switzerland
In Response: We appreciate the interest by Nadig et al. regarding our recent article (1). We used a DualStim® neurostimulator (Life-Tech, Houston, TX); impulse duration was 0.5 ms. The principal aim of our study was to investigate the effect of adding clonidine to bupivacaine 0.5% on the duration of analgesia. Epinephrine was used in all groups. If Nadig et al. believe that the epinephrine could have had an impact on the potential efficacy of clonidine, they are invited to provide some evidence for this assumption. To maintain blinding despite comparisons across route we used a double-dummy design. Again, the trial was strictly controlled inasmuch as all patients received isoflurane. Thus, if there was more hypotension and bradycardia in the clonidine groups, it is very likely that these additional hemodynamic changes were attributable to the clonidine. Our study was designed to identify efficacy and harm of clonidine added to an interscalene block under daily clinical conditions rather than to measure its hemodynamic effects in awake subjects. Thus our data provide an important message for clinicians that are using such blocks associated with general anesthesia in patients who undergo surgery in a semi-sitting position. As the satisfaction scores at 24 h were not different between groups, we decided to provide the data at 48 h only. Finally, the question regarding statistical tests for comparing pain scores is legitimate. We reanalyzed the data using a nonparametric test and obtained nearly identical P values.
References
- Culebras X, Van Gessel E, Hoffmeyer P, Gamulin Z. Clonidine combined with a long acting local anesthetic does not prolong postoperative analgesia after brachial plexus block but does induce hemodynamic changes. Anesth Analg 2001; 92: 199–204.
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