One discussion this week involved the role of evoked potentials in thoracoabdominal aortic (TAA) repair.

Reference: Achouh PE, et al. Role of somatosensory evoked potentials in predicting outcome during thoracoabdominal aortic repair. The Annals of Thoracic Surgery. 2007 Sep; 84(3):782-787.

Summary:  Between January 2000 and April 2005, a study out of Houston, TX, used SSEP monitoring in 444 patients (270 thoracoabdominal aorta and 174 descending thoracic aorta).  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.

Primary findings included:

• 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.
• 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.

Achouh et al (2007) conclude that “intraoperative SSEP monitoring was reliable in ruling out spinal injury in DTA and TAA repair, but had a low sensitivity. Somatosensory evoked potential did not predict delayed ND. Spinal SSEP change was an independent predictor for mortality in DTA and TAA repair and correlated with low preoperative glomerular filtration rate” (p.787).