Objective: To determine the minimal electric threshold of neurostimulation dorsally and ventrally to the interarcuate ligament in the lumbosacral area necessary to cause muscle contraction of the hind limb or tail and determine whether a continuous electrical stimulation applied to an insulated needle during lumbosacral epidural needle placement could be used to distinguish the epidural from the intrathecal space in rabbits.
Animals: 24 New Zealand white rabbits.
Procedures: Rabbits received iohexol (0.2 mL/kg) either dorsally (group 1) or ventrally to the interarcuate ligament in the lumbosacral area (groups 2 and 3). Correct placement of the needle was determined by use of the loss of resistance to injection technique (group 2) or a continuous electrical stimulation (group 3) and confirmed by examination of the iohexol distribution pattern on radiographs.
Results: In all rabbits of group 1, iohexol was injected in the lumbosacral area, outside the epidural space. In groups 2 and 3, iohexol was injected intrathecally. No pure iohexol epidural migration of iohexol was observed. Mean ± SD minimal electric threshold to elicit a motor response was 1.2 ± 0.3 mA, 0.3 ± 0.1 mA, and 0.3 ± 0.1 mA in groups 1, 2, and 3, respectively.
Conclusions and clinical relevance: Neurostimulation was a useful technique to determine correct intrathecal needle placement in rabbits but failed to detect the lumbosacral epidural space when the common technique, used in dogs and cats for the lumbosacral epidural approach, was used.