Anesth Analg 2002;95:780-781
© 2002 International Anesthesia Research Society
LETTERS TO THE EDITOR
Evaluation of a New Posterior Subgluteus Approach to Sciatic Nerve
Ashok Kumar, MD DA, MAMS
Department of Anesthesiology & Pain Management, University College of Medical Sciences & G.T.B. Hospital,, Dilshad Garden, Delhi, India
To the Editor: I read with great interest the article evaluating the efficacy and acceptance of a new posterior subgluteus approach to the sciatic nerve (1). I have some concerns and questions.
First, the authors observed no differences in the failure rate of nerve blocks with the two different approaches. Perhaps an independent observer should have been blinded to the approach used for sciatic nerve block, and thus the possibility of bias could have been removed.
Second, why should the large size of sciatic nerve make the onset of blockade less predictable, especially when the authors used a short-beveled Teflon-coated stimulating needle in association with a nerve stimulator?
Third, patients were asked to grade the discomfort on a 3-point scale; it should also have been graded on a 0–100 mm scale.
Fourth, no complications were encountered with the new posterior approach to sciatic nerve block. However, some consideration should be given to being more discriminative about the type of needle that is used during peripheral nerve blocks, especially if it might help reduce and/or prevent a complication. I believe this is the best way for a thorough evaluation of a new approach to sciatic nerve block.
References
- di Benedetto P, Bertini L, Casati A, et al. A new posterior approach to the sciatic nerve block: a prospective, randomized comparison with the classic posterior approach. Anesth Analg 2001; 93: 1040–4.[Abstract/Free Full Text]
Response
Andrea Casati, MD, and
Pia di Benedetto, MD
Vita-Salute University of Milano, Department of Anesthesiology, Milano, Italy
Department of Anesthesiology, CTO Rome, Italy
In Response: We want to thank Dr. Kumar for his interest in our description of a new posterior approach to the sciatic nerve block (1). As we clearly stated in our discussion, it was a true pity that ". . .the independent observer evaluating the evolution of sensory and motor blocks, as well as its intraoperative efficacy was not blinded to the approach used for sciatic nerve block: this can be considered a shortcoming of our study, because we cannot exclude a bias toward the efficacy of the new subgluteus approach. . .." Nonetheless, Dr. Kumar also has to recognize that open, randomized studies have their own validity and clinical relevance (2). Furthermore, since the patients did not have any expectation and/or experience of the other treatment (the type of approach to the sciatic nerve block), the study can be considered as a single-blinded study. Thus the scoring of patients’ acceptance can be considered as really unbiased. On the other hand, it must be also stressed that it is somehow difficult to hide the shouting of a patient with an ineffective nerve block. Accordingly, the anesthesiologists’ bias about block efficacy was actually minimized by both the surgeons and (even more) the patients.
Similar considerations can be drawn for the scale used to grade patients’ discomfort during the procedure. Dr. Kumar states that we should have used a 10-cm visual analog scale instead of a verbal rating scale; we thank him for his suggestions that may be helpful for future studies. However, Dr. Kumar also must acknowledge that verbal rating scales are widely used and accepted in the international literature, especially to evaluate pain and/or discomfort.
Dr. Kumar was also concerned about our statement on the variability of the onset time of sciatic nerve block. In fact, in our experience the onset time of peripheral nerve blocks is highly variable, and the onset time of sciatic nerve block is usually longer than femoral, which is longer than interscalene. Sometimes we also see a longer onset time after eliciting a good motor response at 0.2–0.3 mA than that observed after eliciting a weak motor response with 0.5 mA. Maybe this is related to our limited experience; however, if we give a look at the literature, we will find too a huge variability in the reported onset times of peripheral nerve blocks, and this variability is much wider for sciatic nerve block (3–5).
The last comment outlined by Dr. Kumar is about the association between the design of stimulating needles and the risk for nerve injury. This is an interesting point, and properly powered, randomized, blinded studies might be advocated to evaluate it. However, before answering this very elegant question we should also understand why so many anesthesiologists throughout the world still insist in performing peripheral nerve blocks with uninsulated needles and the paresthesia technique.
References
- Di Benedetto P, Bertini L, Casati A, et al. A new posterior approach to the sciatic nerve block: a prospective, randomized comparison with the classic posterior approach. Anesth Analg 2001; 93: 1040–4.
- Husler J, Wernecke KD. How to design trials/studies. In: Zbinden AM, Thomson D, eds. Conducting research in anaesthesia and intensive care medicine. Oxford, England: Butterworth-Heineman, 2001: 97–138.
- Chelly JE, Delaunnay L. A new anterior approach to the sciatic nerve block. Anesthesiology 1999; 91: 1655–60.[Web of Science][Medline]
- Davies MJ, McGlade DP. One hundred sciatic nerve blocks: a comparison of localisation techniques. Anaesth Intensive Care 1993; 21: 76–8.[Web of Science][Medline]
- Coventry DM, Todd JG. Alkalinsation of bupivacaine for sciatic nerve blockade. Anaesthesia 1989; 44: 467–70.[Web of Science][Medline]
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