Prevention of spinal cord ischemia by monitoring spinal cord perfusion pressure and somatosensory evoked potentials.

The pressure difference between mean distal aortic pressure (MDAP) and cerebrospinal fluid pressure (CSFP), defined as relative spinal cord perfusion pressure (SCPP), and somatosensory evoked potentials (SEP) were monitored intraoperatively to detect and prevent intraoperative ischemic spinal cord injury in 19 patients who required cross-clamping of the descending thoracic aorta. Temporary axillo-femoral shunt utilizing a 10 mm woven Dacron tube graft was employed in 10 patients and partial cardiopulmonary bypass in nine. Ischemic SEP changes were seen in five patients. Two patients, whose SCPPs were 32 and 35 mmHg, experienced the complete loss of SEP and developed paraplegia. In the other three cases, increase of MDAP and/or withdrawal of cerebrospinal fluid (CSF) were performed to increase the SCPP to more than 40 mmHg when ischemic SEP changes occurred. SEP gradually recovered in two cases. The other patient underwent reimplantation of intercostal arteries since the ischemic SEP changes did not revert. These three patients recovered without any neurological deficit. In the other 14 cases without ischemic SEP changes, SCPP was kept at more than 40 mmHg during aortic cross-clamping. We conclude that the maintenance of SCPP at more than 40 mmHg by increasing MDAP and/or withdrawing CSF is an effective procedure in preventing postoperative paraplegia.