Letters to the Editor: Letters & Announcements
To the Editor:
We read with interest the article by Voelckel et al. (1) and commend the authors for highlighting the importance of routinely determining the lower current threshold at which electrolocation occurs, thus possibly reducing the risk of subsequent neuropathy. The overriding concern of the clinical practitioner (especially the inexperienced one) is to achieve a successful block, and the focus becomes the upper current threshold of electrolocation.
It would be interesting to know whether more attempts at needle insertion and redirection were required in the group randomized to lower current. Such attempts could have increased the risk of direct trauma to the nerve and may have partly accounted for the observed findings.
It would be clinically significant if there is an association between multiple attempts at electrolocation and subsequent nerve damage. This would be particularly important in regional techniques where the motor response significantly affects the incidence of successful surgical anesthesia (e.g., the infraclavicular brachial plexus block), and where multiple-injection techniques are used. The temptation to engage in a prolonged search for the “best” motor response may have to be tempered with the knowledge that such searching may increase the risk of neuropathy. The use of larger gauge needles required for continuous catheter techniques may further increase this risk. Nevertheless, the incidence of transient neurologic dysfunction in a large prospective series of multiple-injection injection techniques for axillary, interscalene, and sciatic-femoral blocks was only 1.7% (2).
A final consideration is the accuracy of nerve stimulators. Significant variance has been demonstrated in most commercial nerve stimulators, particularly at low currents (3,4). Clinicians should take electrical current threshold limits into account.
Ki Jinn Chin, FANZCA, MMed
Victor W. T. Chee, MMed
Department of Anaesthesiology
Tan Tock Seng Hospital
Singapore, Republic of Singapore
1. Voelckel WG, Klima G, Krismer AC, et al. Signs of inflammation after sciatic nerve block in pigs. Anesth Analg 2005;101:1844–6.
2. Fanelli G, Casati A, Garancini P, Torri G. Nerve stimulator and multiple injection technique for upper and lower limb blockade: failure rate, patient acceptance, and neurologic complications. Study Group on Regional Anesthesia. Anesth Analg 1999;88:847–52.
3. Barthram CN. Nerve stimulators for nerve location: are they all the same? A study of stimulator performance. Anaesthesia 1997;52:761–4.
4. Hadzic A, Vloka J, Hadzic N, et al. Nerve stimulators used for peripheral nerve blocks vary in their electrical characteristics. Anesthesiology 2003;98:969–74.