To reduce the incidence of misleading assessments, and to derive criteria for critical spinal cord ischemia during thoracic or thoracoabdominal aortic aneurysm repair, the authors epidurally stimulated and recorded somatosensory evoked potentials (ESEP) below and above, respectively, the spinal segment at risk (electrospinogram).Methods
Epidural somatosensory evoked potentials were analyzed in 100 consecutive patients undergoing resection of aortic aneurysms using two bipolar catheters (stimulation at the L2 level and recording at the T3 level) for the following criteria: 1) the time until ESEP disappeared completely after cross clamping, 2) the duration of complete ESEP loss during and after cross clamping, and 3) the time until ESEP recovered after declamping. Postoperatively, neurologic deficits were evaluated by a neurologist who was unaware of the ESEP recordings.Results
Three types of patients could be identified. First, thirty-one patients neither showed ESEP loss nor neurologic deficits. Second, ESEP loss occurring later than 15 min after cross clamping was associated with a neurologic deficit in 2 of 29 patients (6.9%). And, third, 12 of 40 patients (30%) presented a neurologic deficit when ESEP loss occurred within 15 min after cross clamping. Further indicators of an impending risk were a total ESEP loss greater than 40 min (sensitivity 100%, specificity 68%, positive predictive value [PPV] 35%, and negative predictive value [NPV] 100%), and a recovery of ESEP later than 20 min after declamping (sensitivity 93%, specificity 86%, PPV 52%, and NPV 99%).Conclusions
Epidural somatosensory evoked potentials appeared to be a reasonable intraoperative predictor of postoperative neurologic outcome, and informs surgeons and anesthesiologists about the impending danger at an early state of the operation.