Comparison of evoked spinal potentials by stimulation of the sciatic nerve and the spinal cord.

Spinal cord monitoring during surgery using evoked spinal potentials (ESP) is now popular. In cats, ESPs due to both sciatic nerve (SN-ESP) and spinal cord stimulation (SC-AESP and SC-DESP) were recorded from the epidural space. Both SN-ESP and SC-AESP were compared by parameter studies. Stimulus frequencies up to 100 Hz did not significantly alter the SC-AESP, whereas the later components of the SN-ESP decreased greatly in amplitude. The SN-ESP was more sensitive to asphyxia than the SC-AESP. Augmentation of the ESP occurred approximately 5 minutes after the asphyxia was introduced, which was interpreted as an impending sign of anoxia of the spinal cord. The SN-ESP had more potentials arising from synaptic and postsynaptic activities, while the SC-AESP was mainly derived from the spinal tracts. To monitor the function of the spinal cord, both methods should be used.