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LETTER TO THE EDITOR

Stimulating Catheters in Continuous Popliteal Block

Anesthesiology Department, Valme Hospital, ctra. Cádiz s/n, Seville, Spain, amartnavas{at}yahoo.es

To the Editor:

Casati et al. (1) contend that stimulating catheters are more useful than nonstimulating catheters in continuous posterior popliteal sciatic nerve block. However, there are several questions that need to be addressed to interpret their results, specifically:

1. Given that the sciatic nerve divides at a mean distance of 60.5 ± 27.0 mm above the popliteal fossa crease (2) in their study, how far was the puncture site above the crease?

2. Could the catheter tip position have affected the onset time for sensory and motor block?

3. What motor response was observed with the needle and the stimulating catheter? Was there any difference in the motor response observed with the needle and with the stimulating catheter?

4. Why was the onset of sensory and motor block shorter for the common peroneal nerve than for the tibial nerve? Specifically, was the catheter tip placed closer to the common peroneal nerve?

5. If "there was no difference in the quality of pain relief at rest and during motion" in the two groups, then why was more rescue opioid analgesia required during the study period in the nonstimulating group?

6. Why was the femoral block placed? We can speculate that it might be for relief of tourniquet pain or to provide sensory loss in the distribution of the internal saphenous nerve.

7. When subjects experienced pain, where was it located? Could pain have been attributed to failure of the femoral block, leaving the distribution of the saphenous nerve sensate, rather than failure of the popliteal block?

8. Continuous popliteal block using the posterior approach may entail different technical problems linked to the durability of the catheter in this position in up to 25% of cases (3). Did the authors observe the same incidence and the same technical problems using stimulating and nonstimulating catheters?

References

1. Casati A, Fanelli G, Koscielniak-Nielsen Z, et al. Using stimulating catheters for continuous sciatic nerve block shortens onset time of surgical block and minimizes postoperative consumption of pain medication after hallux valgus repair as compared with conventional nonstimulating catheters. Anesth Analg 2005;101:1192–7.[Abstract/Free Full Text]
2. Vloka JD, Hadzic A, April E, Thys DM. The division of the sciatic nerve in the popliteal fossa: anatomical implications for popliteal nerve blockade. Anesth Analg 2001;92:215–7.[Abstract/Free Full Text]
3. Liu SS, Salinas FV. Continuous plexus and peripheral nerve block for postoperative analgesia. Anesth Analg 2003;96:263–72.[Free Full Text]

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