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LETTER TO THE EDITOR

Stimulating Catheters: A Thing of the Past?

Royal Liverpool Children's Hospital; Liverpool, UK; amywalker{at}doctors.org.uk

To the Editor:

Drs. van Geffen and Gielen (1) reported that a combination of ultrasound and nerve stimulation facilitated identification of the sciatic nerve and catheter position in 10 children aged 2–14 yr. Their technique involved placement of a stimulating needle combined with direct ultrasound guidance (short axis) prior to blind advancement of a stimulating catheter. The success of the block was predicted after observing the spread of local anesthetic using ultrasound.

We have placed 31 sciatic nerve catheters in 29 patients ranging from 3 to 17 yr. Our technique involves identification of the nerve using a Micromaxx ultrasound machine and HFL 38 13–6 MHz probe (Sonosite, Bothel, WA). We used an 18 gauge 51 mm insulated Tuohy needle (Braun, Melsungen AG) with a 20-gauge polyamide radiopaque catheter. Using a short axis needle-probe technique, the needle is initially positioned lateral to the sciatic nerve where 25%–33% of the total local anesthetic is injected. The needle is then withdrawn and directed medial to the nerve and the remaining local anesthetic injected. The catheter is then threaded to a maximum of 3 cm beyond the needle. Catheter position is checked by injection of either 1–2 mL of saline or 1 mL of air (seen as a hyperechoic "flash") (2). Of the 29 patients in our series, three went back to the ward with a nurse-controlled analgesia system and two others required additional opiate (a single doses of morphine).

The rationale for using stimulating catheters is that at the point of optimal synchronous motor twitching, the tip of the catheter must lie very close to the nerve. Injection of local anesthetic at this point should therefore produce an effective nerve block. Drs. van Geffen and Gielen comment that with the application of ultrasound, electrical nerve stimulation may no longer be needed and that the only predictor for a successful block is circumferential spread of local anesthetic around the nerve. We not only agree with this comment but believe that stimulating catheters are not only redundant in this setting but potentially increase the risk of nerve damage. Urmey and Stanton (3) found that paraesthesia was elicited before a motor response in 70% of patients undergoing interscalene block. Sensory and motor fibers within large peripheral nerves may be anatomically separate. It could be possible, therefore, for a needle to enter a nerve without contacting any motor neuronal tissue. A recent article by Bigeleisen (4) suggests that puncture of peripheral nerves and injection of small volumes of local anesthetic do not lead to neurological injury. However his case series is relatively small and we believe that this suggestion should be treated cautiously until further randomized. controlled evidence has been sought. One paper (5) found no statistically significant difference in block success when comparing placement of continuous femoral nerve blocks with nonstimulating and stimulating catheters.

Drs. van Geffen and Gielen also comment that inexperienced residents can quickly acquire "hit-the-target" technical skill using a simulated interventional procedure model. This may be true, but in our experience it takes somewhat longer if the objective is to train juniors to consistently identify nerve tissue and become sufficiently proficient in the manipulation of a needle under ultrasound guidance for safe practice.

REFERENCES

1. van Geffen GJ, Gielen M. Ultrasound-guided subgluteal sciatic nerve blocks with stimulating catheters in children: a descriptive study. Anesth Analg 2006;103: 328–33.[Abstract/Free Full Text]
2. Sandhu NS, Capan LM. Ultrasound-guided infraclavicular brachial plexus block. Br J Anaesth 2002;89:254–9.[Abstract/Free Full Text]
3. Urmey WF, Stanton J. Inability to consistently elicit a motor response following sensory paraesthesia during interscalene block administration. Anaesthesiology 2002; 96:552–4.[Web of Science][Medline]
4. Bigeleisen PE. Nerve puncture and apparent intraneural injection during ultrasound-guided axillary block does not invariably result in neurologic injury. Anesthesiology 2006;105:779–83.[Web of Science][Medline]
5. Salinas FV, Neal JM, Sueda LA, et al. Prospective comparison of continuous femoral nerve blockade 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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