Surgical monitoring of spinal cord function: cauda equina stimulation technique.

Spinal cord and subcortical brain stem evoked potentials had an amplitude at least 2 times higher when the cauda equina rather than bilateral peripheral nerves was stimulated. Cauda equina stimulation is indicated when potentials to peripheral nerve stimulation are absent or are too low in amplitude to permit reliable surgical monitoring. The technique is essentially without risks, but should be performed with a small lumbar puncture needle (21 to 22 gauge), and is contraindicated in patients with general infections, increased cerebrospinal fluid pressure, or a hemorrhagic tendency (thrombocytopenia or anticoagulant therapy).