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Transcranial Motor Evoked Potentials Monitoring Is Better Than Somatosensory Evoked Potentials Monitoring for Detection of Spinal Cord Ischemia in Rat Aortic Occlusion Model
Manabu Kakinohana, M.D., Ph.D.; Takeshi Sasara, M.D.; Tetsuya Kawabata, M.D.; Seiya Nakamura, M.D.; Kazuhiro Sugahara, M.D., Ph.D.
Anesthesiology, Faculty of Medicine, University of the Ryukyus, Nishihara, Okinawa, Japan
Introduction : Somatosensory Evoked Potentials (SEPs) is the most popular monitoring for the function of spinal cord during thoracoabdominal aortic replacement surgery. Transcranial Motor Evoked Potentials Monitoring (MEPs) also provides a method for monitoring the functional integrity of descending motor pathways during thoracoabdominal aortic replacement surgery. In the present experiment using aortic occlusion model in rat (1), we compare between MEPs and SEPs to evaluate which method is the most appropriate for detecting spinal ischemia after aortic occlusion and neurological outcome during reperfusion.

Materials and Methods : After Animal Care and Use Committee approval (University of the Ryukyus) male SD rats weighing 350 – 400 g were studied. In rats anesthetized ketamine, spinal ischemia (10 min) was induced by the occlusion of thoracic aorta combined with systemic hypotension (40 mmHg). MEPs were recorded from the right soleus muscle after transcranial-electrical stimulation (100 – 120 V: 5 train-pulse stimulation) before, during ischemia (2, 6, 9 min), at 15, 30 min and 72 hrs after reflow. SEPs were recorded from the epidural space of Th10 level after the left sciatic nerve stimulation. At 3 days of reperfusion animals were perfusion fixed and spinal histopathological changes were determined using Nissl staining following the assessment of neurological outcome. Changes of amplitude in MEPs and SEPs after aortic occlusion compared with baseline were statistically analyzed using one-way repeated measures ANOVA followed by the Dunnett test.

Results : MEPs disappeared within 2 min after aortic occlusion. In SEPs, however, it took over 6 min after aortic occlusion for 50 % reduction from the baseline. Either MEPs or SEPs was returned back to baseline at 15 min after reflow. Althogh the evoked potential waves from both of the monitorings could be identified at 72 hrs of reflow, all rats showed the spastic paraplegia at this time. Histopathological analysis of the spinal cords in lumbosacral segments revealed a selective loss of small interneurons localized predominantly in the intermadiate zone.

Comments : Our results suggest that MEPs can idetify the presence of spinal ischemia during aortic occlusion more rapidly than SEPs, but neither MEPs nor SEPs can not predict an irreversible ischemic spinal cord injury. We emphasize that MEPs is the better method for detecting spinal cord ischemia, but not for predicting ischemic spinal cord injury.

References : (1) Taira Y and Marsala M. Stroke 1996:1850-8

Anesthesiology 2002; 96: A581