SOMATOSENSORY-EVOKED POTENTIAL, A PROGNOSTIC TOOL FOR THE RECOVERY OF MOTOR FUNCTION FOLLOWING MALPERFUSION OF THE SPINAL-CORD - STUDIES IN DOGS

The potential usefulness of somatosensory evoked potential monitoring during aortic cross-clamping is slowly being realized. In addition, the protection of endangered spinal nervous tissue during aortic cross-clamping has not been sufficiently evaluated. To test the pharmacologic protective efficacy of various agents, we recorded spinal evoked somatosensory potentials (bipolar epidural catheter) in dogs under controlled conditions (N2O/O2-enflurane anesthesia) following clamping of the aorta for 1 hour. There were 5 groups of animals: those treated with different medications, such as prostaglandin E1 (PGE1), prostacyclin (PGI2), superoxide dismutase (SOD), and PGE1 plus SOD for pharmacologic protection during ischemia, and the controls. The time to recovery of evoked potentials during the reperfusion period was 36 minutes in the controls, 15.9 minutes in the SOD group (p < 0.01), 12.5 minutes in the PGE1 group (p < 0.001), 10.8 minutes in the PGI2 group (p < 0.001), and 3.8 minutes in the combination group (p < 0.001). In addition, treatment resulted in a better neurologic outcome on the seventh postoperative day when compared with the control group. While in the control group only 1 animal could walk (9%), 7 of 12 in the PGE1 group (58%), 4 of 12 in the SOD group (33.8%), 8 of 12 in the PGI2 group (66.7%), and all animals in the combination group (100%) could walk. We computed an exponential correlation that related the mean time of potential recovery during reperfusion with Tarlov scoring (grade 0 = paraplegia; grade 1 = paraplegia with little movements; grade 2 = paraparesis; grade 3 = paraparesis with some problems; grade 4 = normal motor function) in the various groups. On the seventh postoperative day r = 0.97 and the regression equation was y = 50.6 x 10(-0.28x). The correlation reflects a close relationship between late postoperative outcome of motor function and early intraoperative regeneration of somatosensory potentials after declamping. We conclude that (1) spinal evoked potential can be used as a prognostic tool to indicate recovery of motor function of the lower extremities after aortic clamping, and (2) during aortic cross-clamping the endangered spinal cord can be protected by means of pharmacologic treatment.