Use of somatosensory evoked potentials for thoracic and thoracoabdominal aortic resections

Despite tremendous development in surgical and anesthetic techniques, resection of the thoracic and thoracoabdominal segments of the aorta remain associated with the risk of paralysis. Routine use of somatosensory-evoked potential (SEP) monitoring in patients undergoing surgery of the thoracic aorta has become a standard intra- and postoperative procedure at our institution since its first use in 1993.

One hundred forty nine (149) thoracic aortic operations were performed during January 1993 through January 1998 using SEP-directed serial sacrifice of paired intercostal arteries. Full, partial, or no cardiovascular bypass was variably used, dictated by anatomy; 49 patients required deep hypothermic circulatory arrest (DHCA). Patients were monitored during both the intraoperative procedure as well for the post-anesthesia period until neurologic stability and/or ability to reproducibly demonstrate lower extremity neurologic competency was established. Postoperative neurologic function was compared to ischemic intervals, extent of aortic resection, number of intercostal arteries sacrificed, type of perfusion, and underlying aortic pathology.

Overall mortality in the group was 13 patients (8.7%), with no one cause predominating. Nine patients sustained permanent paraplegia, only 1 of whom lost SEPs during the procedure. Abnormal SEPs were seen in 19 patients, 14 of whom had normal neurologic function after awakening. Three of 19 (15.8%) developed late paraplegia that resolved with medical therapy. Eleven patients (7.4%) developed cerebrovascular accidents (CVA), with the majority (8) appearing in the group undergoing DHCA. The risk of CVA was significantly higher in DHCA patients (p < 0.01) than other patients. No patient with CVA had abnormal SEPs; 4 DHCA patients developed abnormal SEPs, 1 with permanent paralysis.

The routine use of SEP monitoring during thoracic and thoracoabdominal aortic surgery as well as during the postoperative period may be useful in decreasing the observed incidence of paraplegic events associated with these procedures.