Spinal function monitoring by evoked spinal cord potentials in aortic aneurysm surgery

Evoked spinal cord potentials (ESCPs) were monitored in 12 patients who underwent repair of thoracoabdominal aortic aneurysm with a high risk of spinal ischemia. A pair of bipolar catheter electrodes were introduced into the epidural space, one at the level of the C5-T2 vertebrae and the other at the level of T11-L2. Conductive mixed ESCP in seven patients, conductive sensory ESCP in one patient, and segmental descending ESCP in three patients were observed by applying a rectangular electric current to one of each pair of epidural electrodes and recording through the other. Segmental ESCP in response to posterior tibial nerve stimulation was observed in one patient. Following aortic cross-clamping, the I wave of conductive mixed ESCPs gradually decreased in amplitude with latency prolongation in five of the seven patients and disappeared in one of these five; transient augmentation of amplitude was observed before eventual decline in four of these five patients. The N wave of segmental descending ESCP subsequently flattened in two of the three patients and the N₁ wave of segmental ESCP in the one patient. Three of the four patients in whom the ESCPs disappeared during aorta clamping recovered the ESCPs after declamping and showed no neurological disorders postoperatively. Intraoperative ESCP monitoring appears to be useful to detect spinal cord ischemia in the early stage and to alert surgeons and anesthesiologists so that timely resuscitative steps can be taken.