Evoked Spinal Cord Potential (ESP) for Detection and Prevention of Spinal Cord Ischemia During Aortic Cross-Clamping.

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Evoked spinal cord potential (ESP) was recorded and analyzed in order to detect and prevent the paraplegia caused by spinal cord ischemia during thoracic aortic cross-ciamping.(1) Experiment.Material and Methods: Adult dogs underwent continuous monitoring of ESP before, during, and after aortic cross-clamping. Stimulating electrodes were placed in the epidural space near L-1, sensing electrodes were placed in the intervertebral disc between T-3 and T-5. 5 to 100 responses were averaged to construct %e%sP..Results: ESP responses to aortic cross-clamping were categorized into three types: loss of ESP during aortic cross-clamp (type 1),'no change in ESP during cross- clamp (type 2), and transient depression and return of ESP during cross-clamp (type 3). All dogs of type 1 response demonstrated paraplegia, where-as no dog of type 2 response showed paraplegia. Some dogs of type 3 response demonstrated spastic paraplegia. Although cross-clamp was removed 10 minutes after ESP became 20% of the previous amplitude in another series of type 1 dogs, paraplegia was not prevented.Histological examination revealed infarction of the grey matter of the spinal cord below T-8 in the dogs with paraplegia.Selective perfusion of the intercostal arteries furing cross-clamping and intraaortic infusion of vasodilators seemed promising to prevent spinal cord ischemic injury.(2) PracticeESP was monitored in 30 patients who underwent thoracic aortic surgery.23 patients showed type 2 response. ESP was slightly depressed in 4 patients. 3 patients demonstrated type 1 response; temporary bypass was re-established in one case, cross-clamp could be released within a few minutes after ESP loss in other two cases. No paraplegia was experienced.We have invented a special bypass tube to perfuse intercostal arteries during aortotomy in case of prolonged type 1 response which strongly suggests spinal cord ischemia.