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LETTER TO THE EDITOR

Stimulating Catheters in Continuous Popliteal Block

University of Parma, Department of Anesthesiology and Pain Therapy, Ospedale Maggiore di Parma, Parma, Italy, acasati{at}ao.pr.it (Casati) Catholic University of Lovanio, St-Luc Hospital, Brussels, Belgium (Singelyn) Copenhagen University Hospital, Copenhagen, Denmark (Koscielniak-Nielsen)

In Response:

We thank Dr. Navas for his observations (1) on our recent manuscript (2). Results of our prospective, randomized, blinded trial suggested that stimulating catheters can provide some minor advantages over nonstimulating catheters in continuous posterior popliteal sciatic nerve block. We agree with Dr. Navas that although the observed reduction in onset time was statistically significant, its clinical relevance is questionable. However, the use of a stimulating catheter reduced the amount of local anesthetic and rescue pain medication required to produce the same quality of postoperative analgesia as is provided with a nonstimulating catheter.

In our investigation the sciatic nerve was reached 10 cm proximal to the popliteal crease before the 2 main branches of the sciatic nerve divide. One explanation for the shorter onset time was that the final position of the catheter tip was closer to the nerve when direct stimulation through the catheter was used to identify correct positioning. In this study we placed the catheter at the stimulation of either the tibialis or common peronealis nerve. Even though Taboada et al. (3) demonstrated better performance when the tibial twitch was used instead of the common peroneal twitch, we were not able to find differences in results by stratifying for the twitch used for catheter placement. However, our study was not designed to answer this question.

The shorter onset time observed in the common peroneal distribution, as compared with the tibial distribution, may have been attributable to the different size of the two nerves. This agrees with findings reported by Taboada et al. (3).

The quality of pain relief was measured at fixed intervals. Both groups had adequate pain relief, and we did not observe differences in pain relief. However, patients with nonstimulating catheters achieved adequate pain relief by consuming more local anesthetic and more rescue tramadol. This could be evidence that the final position of the catheter tip was closer to the nerve with the stimulating than nonstimulating catheters. This hypothesis is supported by findings of Salinas et al. (4), who showed in volunteers that the minimum stimulating current through the catheter resulting in a proper muscular twitch was lower when the catheter was placed with a stimulation-guided technique than that observed after placing the catheter with a "conventional" blind technique.

The femoral block was placed for tourniquet pain and was not relevant postoperatively because the block dissipated quickly. Pain after surgery was related to the sciatic nerve distribution and not the saphenous one.

Finally, we agree with Dr. Navas that keeping the catheter in place is one of the major problems in failure rate of continuous peripheral nerve blocks. We did not observe differences between stimulating and nonstimulating catheters with respect to this technical problem.

References

1. Navas AM. Stimulating catheters in continuous popliteal block. Anesth Analg 2006;102:xxx.
2. 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]
3. Taboada M, Atanassoff PG, Rodriguez J, et al. Plantar flexion seems more reliable than dorsiflexion with Labat's sciatic nerve block: a prospective, randomized comparison. Anesth Analg 2005;100:250–4.[Abstract/Free Full Text]
4. Salinas FV, Neal JM, Sueda LA, et al. Prospective comparison of continuous femoral nerve block with nonstimulating catheter placement versus stimulating catheter-guided perineural placement in volunteers. Reg Anesth Pain Med 2004;29:212–20.[Web of Science][Medline]

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