Strategies to prevent neurologic deficit based on motor-evoked potentials in type I and II thoracoabdominal aortic aneurysm repair

Purpose: Motor-evoked potentials (MEPs) were monitored during thoracoabdomi nal aortic aneurysm (TAAA) repair to assess spinal cord ischemia and evalua te the subsequent protective strategies to prevent neurologic deficit. Methods: Between January 1996 and December 1997, 52 consecutive patients wi th type I (n = 24) and type II (n = 28) TAAA underwent surgery (mean patien t age, 60 years; range, 21-78 years). The surgical protocol included left h eart bypass, cerebrospinal fluid drainage, and monitoring transcranial myog enic MEPs. When spinal cord ischemia was detected, distal aortic pressure a nd mean arterial pressure were increased. By means of sequential crossclamp ing, MEPs were used to identify critical intercostal or lumbar arteries. Results: Reproducible MEPs could be recorded in all patients, and spinal co rd ischemia was detected within 2 minutes. During distal aortic perfusion, 14 patients (27%) showed rapid decrease in the amplitude of MEPs to less th an 25% of baseline, indicating spinal cord ischemia, which could be correct ed by increasing distal aortic pressure. The mean distal aortic pressure to maintain adequate cord perfusion was 66 mm Hg; however, it varied among in dividuals between 48 and 110 mm Hg. In 24 patients (46%), MEPs disappeared after segmental clamping and returned after reattachment of intercostal art eries. In 9 patients (17%), MEPs disappeared completely, but no intercostal arteries were found. After aortic endarterectomy; 6 or 8 mm Dacron grafts were anastomosed to intercostal arteries, and MEPs returned after reperfusi on. Using this aggressive surgical approach based on MEPs, no early or fate paraplegia occurred in this series. Conclusion: Monitoring of MEPs is an effective technique to assess spinal c ord ischemia. Operative strategies based on MEPs prevented neurologic defic its in patients treated for type I and II TAAA.