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Correspondence  |   November 2003
Posterior Approach to the Sciatic Nerve: Can “Common Sense” Replace Science and Logic?: In Reply:—
Author Notes
  • Cook County Hospital, Chicago, Illinois.
Article Information
Correspondence
Correspondence   |   November 2003
Posterior Approach to the Sciatic Nerve: Can “Common Sense” Replace Science and Logic?: In Reply:—
Anesthesiology 11 2003, Vol.99, 1238-1239. doi:
Anesthesiology 11 2003, Vol.99, 1238-1239. doi:
In Reply:—
I appreciate Dr. Candido et al.  taking the time to comment on my article. The concept that a sciatic block can be performed on adults of different sizes at a fixed distance from the midline is understandably difficult to accept, at first. What is being measured is the distance from the midline to the lateral side of the ischium. This distance becomes fixed in adults and represents a fraction of the bony pelvis width. Dealing with just part of a diameter that is already fairly constant in adults, 1,2 plus the large size of the nerve, help to minimize any potential differences. In response to the authors’ concerns:
  1. A recently quoted 61% of asymmetry in brachial plexus 3 supports the potential for any nerve asymmetry. Although I did found no differences in nerve location, I did find asymmetry of the nerve itself (two nerves in one sheath, one on the contralateral side).

  2. Studying 12 cadavers (eight female, four male) might not be enough, as the study on 10 cadavers by Sukhani and Candido shows. 4 

  3. The range of measurements was narrow (9.7–10.3 cm); thus “inter- or intraindividual variability” was not a factor.

  4. Claiming 60% of “multiple attempts” is misleading. The fact is that 85% of the patients (17 out of 20) needed three attempts or fewer, and all were completed within six attempts, using a single skin puncture in each case. The population was 35% obese (BMI ≥ 30) and 80% overweight (BMI ≥ 25).

  5. My technique makes finding the nerve easier, but it does not influence success one way or the other, after the nerve is identified. A 90% success rate is better appreciated after reviewing the “failed” blocks: (i) Obese woman (BMI, 33.5) in whom only an intermittent response could be elicited (needle short for her size). This case could have been thrown out on that basis. An early incision at 16 min proved that the block was still incomplete. What is remarkable about this case is not that it “failed” but that the nerve was found at 10 cm in a large buttock. (ii) Young, nervous patient whose block took one attempt. Her “discomfort” 10 min after the incision could have been managed with additional narcotics. However, a successful block was limited to no more than 100 μg of fentanyl.

  6. The statement “variations in the hip width reflects soft tissue, not bony, differences between the sexes” is paramount to understand why a block can be performed at 10 cm in both sexes. The contour of the buttocks would indeed alter this measurement, which is why it must be done in a straight line from the midline, disregarding the curvature of the buttocks.

  7. The authors would have preferred my “Clinical Stage” to be called “Clinical Study,” but they liked my “Anatomy Stage.” This objection exceeds the intended purpose of the study.

  8. The results obtained in 20 patients confirmed my anatomy findings. Currently, with more than 100 blocks performed, my conviction is even stronger. On a few occasions, I have even managed to make more than six attempts to find the sciatic nerve (heresy!). However, invariably it has been found in close proximity to the original insertion point and no skin reinsertion has been necessary.

  9. The type of response and the output at which it is elicited (is 0.5 mA significantly different from 0.6 mA?) are indeed very important factors but are unrelated to whether the sciatic nerve is located at 10 cm from the midline.

  10. I chose the incision (all within 29 min) as the main test for success because it is highly objective, but I understand that others would choose differently. However, calling it “questionable ethically” is not worth a response and makes me wonder whether the authors are truly bringing these objections with a scientific purpose in mind.

  11. Those who received successful blocks were not given more than the stated amounts of sedation. Inferring from this that “the amount of sedation administered to individual patients was not carefully monitored” is simply wrong.

  12. When the operator was ready, the timer was turned on and was never stopped until the incision. When reaching a preestablished goal (e.g.  , first sciatic response), the designated person would simply enter the actual reading (e.g.  , 1:06) on the protocol sheet and continue observing until the next goal was met. The time intervals were clear (or so I thought). “First sciatic” for instance, measured the time to elicit the first sciatic response, obviously accounting for any necessary reposition(s). Later, outside the operating room, the time intervals were easily calculated. The authors’ claim that “this approach might have involved a great deal of ‘estimating’ is bad “estimation” on their part.

  13. When reposition was necessary, “the actual distance  from the intergluteal sulcus to the needle entry point at the successful  attempt was not reported.” That is right. Because every block was started and completed through a single skin puncture, there was nothing to report.

  14. Postoperative analgesia, although important, had nothing to do with my study goal.

  15. When I said that successful blocks were performed on a 147-cm tall Hispanic woman and a 196-cm tall Caucasian male, I did not intend to start a discussion on race. I am confident that most of the readers understood that my technique applies to a large and diverse population.

  16. Calling this new approach “speculation” is refuted by the now overwhelming clinical evidence and the many anesthesiologists who have tried it with success (communications on file).

In summary, it is reassuring to know that even those who are reluctant to believe that a sciatic block in adults could be performed at 10 cm from the midline, sans geometry, offer no evidence to the contrary other than their disbelief. I would encourage them to try it, understanding that it could become addictive.
References
Cunningham's Textbook of Anatomy, 5th edition. Edited by Robinson A. New York, William Wood and Company, 1928, pp 258
Hall J, Froster-Iskenius U, Allanton J: Handbook of Normal Physical Measurements. Oxford, Oxford University Press, 1989, pp 254–8
Neal J, Hebl J, Gerancher J, Hogan Q: Brachial plexus anesthesia: Essentials of our current understanding. Reg Anesth Pain Med 2002; 27: 402–28Neal, J Hebl, J Gerancher, J Hogan, Q
Franco CD, Tyler SG: Modified subgluteal approach to the sciatic nerve. Anesth Analg 2003; 97: 1197–8Franco, CD Tyler, SG