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Department of Anesthesiology and Pain Medicine, University of Alberta, Edmonton, Alberta, Canada
Address correspondence and reprint requests to Ban C. H. Tsui, MSC, MD, FRCP(C), Department of Anesthesiology and Pain Medicine, University of Alberta Hospitals, 3B2.32 Walter Mackenzie Health Science Centre, 8440-112 St., Edmonton, Alberta, Canada T6G 2B7. Address e-mail to btsui{at}ualberta.ca
We designed this study to determine the threshold current for nerve stimulation of an insulated needle in the epidural space. The intended dermatome was identified using the bony landmarks of the spine. An 18-gauge insulated Tuohy needle was inserted perpendicularly to the skin and advanced until "loss of resistance" was felt. A nerve stimulator was then connected to the insulated needle. Twenty patients were studied using an insulated Tuohy needle and one patient was studied using a noninsulated Tuohy needle. Muscle twitch was elicited with a current of 11.1 ± 3.1 mA (mean ± SD) in all patients in which an insulated needle was used. Muscle twitches were within 2 myotomes of the intended level (based on bony landmarks). Muscle twitch was not elicited with a noninsulated needle. After catheter threading, positive stimulation tests were elicited via epidural catheters in all patients (4.9 ± 2.3 mA). Postoperative radiograph confirmed all catheter placements within 2 myotomes of the muscle twitches. Electrical stimulation may be a useful adjuvant tool to loss of resistance for confirming proper thoracic epidural needle placement. The threshold current criteria for an insulated needle (617 mA) would be higher than the original Tsui test criteria described for an epidural catheter (110 mA) in the epidural space.
IMPLICATIONS: Electrical stimulation may be a useful adjuvant tool for confirming proper thoracic epidural needle placement. The threshold current for an insulated needle is higher than the original Tsui test criteria described for an epidural catheter in the epidural space.
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