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PEDIATRIC ANESTHESIA

Threshold Current of an Insulated Needle in the Intrathecal Space in Pediatric Patients

Ban C.H. Tsui, MD MSc FRCP(C)^*, Alese M. Wagner, BSc^*, Kirsten Cunningham, MB, ChB^*, Shirley Perry, MScN, Sunil Desai, MB, ChB, FRCP(C), and Robert Seal, MD, FRCP(C)^*

*Department of Anesthesiology and Pain Medicine, University of Alberta, Edmonton, Alberta, Canada; and Department of Pediatric Oncology, Stollery Children's Hospital, 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 Street, Edmonton, Alberta, Canada T6G 2B7. Address e-mail to btsui{at}ualberta.ca.

A threshold current of <1 mA has been suggested to be sufficient to produce a motor response to electrical stimulation in the intrathecal space. We designed this study to determine the threshold current needed to elicit motor activity for an insulated needle in the intrathecal space. Twenty pediatric patients aged 7.3 ± 3.9 yr scheduled for lumbar puncture were recruited. After sedation with propofol, patients were turned to the lateral position and an 18-gauge or 20-gauge introducer needle was placed at the L4-5 level through which an insulated 24-gauge Pajunck unipolar needle (with a Sprotte tip and stylet) was inserted. The needle was advanced into the intrathecal space as suggested by the presence of a "pop." At this point, a nerve stimulator was attached to the insulated needle and the current was gradually increased until motor activity was evident. The needle hub was checked for cerebrospinal fluid. If cerebrospinal fluid was not present, the needle was advanced further until cerebrospinal fluid was present. The threshold current was retested. The mean current in the intrathecal space required to elicit a motor response was 0.6 ± 0.3 mA (range, 0.1–1 mA). In 19 patients, the twitches were observed at the L4-5 myotomes and 1 patient had twitches at L2. Twitches were observed unilaterally in 19 children and bilaterally in one child. This confirms the hypothesis that the threshold current in the intrathecal space is <1 mA and that it differs significantly from the threshold currents reported for electrical stimulation in the epidural space.

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999