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THRESHOLD CURRENT IN THE INTRATHECAL SPACE OF CHILDREN

Department of Anesthesiology and Pain Medicine and Pediatric Oncology, University of Alberta Hospital and
^* Stollery Children’s Hospital, 8440-112 Street, Edmonton, Alberta, T6G 2B7

INTRODUCTION

Previously, it was hypothesized that with electrical stimulation it would require < 1mA to observe motor activity in the intrathecal space.^1,2 This has been shown in individual case reports and in a porcine model, but never in a formal study. This study was designed to determine the threshold current necessary to elicit motor activity in the intrathecal space of pediatric oncology patients undergoing diagnostic or therapeutic lumbar punctures.

METHODS

After IRB approval, pediatric oncology patients scheduled for lumbar puncture were recruited. Following sedation with propofol, patients were turned to the lateral position and prepped in a sterile fashion. An 18- or 20-gauge introducer was inserted at the L4-5 level followed by an insulated 24-gauge Pajunck unipolar needle (with a Sprottetip and stylet). The needle was then advanced into the intrathecal space and confirmed by the presence of cerebrospinal fluid (CSF). At this point, an independent observer attached the insulated needle to a nerve stimulator and the current was increased until the minimal threshold current for motor activity was observed.

RESULTS

Twenty pediatric oncology patients (ASA II or III) aged 7.9 ± 4.0 years (1.6 yrs-16 yrs) were studied. The mean patient weight was 28.2 ± 15.0 kg. There were 10 male and 10 female patients. The mean current to elicit motor activity in the intrathecal space was 0.6 ± 0.3 mA (range 0.1-1mA). Nineteen twitches were at the L3-5 myotomes and one patient had twitches at L2. 19 twitches were unilateral and 1 was bilateral.

DISCUSSION

This study demonstrated that the mean threshold current necessary to elicit motor response in the intrathecal space of pediatric patients was 0.6 ± 0.3mA and confirms the hypothesis that the minimal threshold current in the intrathecal space is < 1mA. As this differs from the threshold currents reported for electrical stimulation in the epidural space, one may potentially distinguish the epidural space from the intrathecal space.

REFERENCES

1 Anesth Analg 2001;93:1152–5.[Abstract/Free Full Text]

2 Anesthesiology 2002; A723.

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