Role of somatosensory evoked potentials in predicting outcome during thoracoabdominal aortic repair

Background. Clinical utility of somatosensory evoked potentials ( SSEP) in descending thoracic and thoracoabdominal aortic repair is debated. We reviewed our practical experience with SSEP in descending thoracic and thoracoabdominal aortic repairs. Methods. Between January 2000 and April 2005, we used SSEP monitoring in 444 patients ( 270 thoracoabdominal aorta and 174 descending thoracic aorta). Median age was 68 years; 36% were female. Only changes of spinal origin were analyzed. Changes were classified as ( 1) no change, ( 2) transient changes that returned to baseline by the end of the procedure, or ( 3) persistent changes that did not return to baseline by the end of the procedure. Results. Somatosensory evoked potential changes occurred in 87 ( 19.6%) patients; 22 ( 25%) of these did not return to baseline. Immediate neurologic deficit occurred in 8 of 444 patients ( 1.8%); five deficits ( 5 of 87; 5.8%) occurred in patients with SSEP changes, compared with three deficits ( 3 of 357; 0.8%) in patients without changes. Odds ratio for this comparison was 7.2 ( p < 0.002). Somatosensory evoked potential was a poor screening tool for neurologic deficit, with a sensitivity of 62.5% and specificity 81.2%. Negative predictive value was 99.2%, indicating a very low event probability in the absence of SSEP changes. Delayed neurologic deficit occurred in 3.2% and was not related to SSEP changes. Somatosensory evoked potential changes were also associated with increased 30- day mortality and low glomerular filtration rate. Conclusions. Intraoperative SSEP monitoring was reliable in ruling out spinal injury in descending thoracic and thoracoabdominal aortic repair, but had a low sensitivity. It did not predict delayed neurologic deficit. Spinal SSEP change was an independent predictor of mortality and correlated with low preoperative glomerular filtration rate.