Multilevel somatosensory evoked potentials and cerebrospinal proteins: indicators of spinal cord injury in thoracoabdominal aortic aneurysm surgery

Objective: Multilevel somatosensory evoked potentials (SSEP) and the release of biochemical markers in cerebrospinal fluid (CSF) were investigated to identify patients with spinal cord ischemia during thoracoabdominal aortic repair and/or a vulnerable spinal cord during the postoperative period. Methods: Thirty-nine consecutive patients undergoing elective aneurysm repair using distal aortic perfusion and cerebrospinal fluid drainage were studied. Continuous SSEP were monitored using nerve stimulation of the right and left posterior tibial nerves with signal recording at the level of both common peroneal nerves, the cervical cord and at the cortical level. CSF concentrations of the markers glial fibrillary acidic protein (GFAp), the light subunit of neurofilament triplet protein (NFL), and S100B were determined at different time points from before surgery until 3 days postoperatively. Results: SSEP indicated spinal cord ischemia in two patients leading to additional intercostal artery reattachments. In one of them the signal loss was permanent and the patient woke up with paraplegia. In the other the signal returned but the patient later developed delayed paraplegia. Three patients without SSEP indications of spinal cord ischemia during surgery later developed delayed paraplegia. The patients with spinal cord symptoms had significant increases, during the postoperative period of CSF biomarkers GFAp (571-fold), NFL (14-fold) and S100B (18-fold) compared to asymptomatic patients. GFAp increased before or in parallel to onset of symptoms in the patients with delayed paraplegia. Conclusions: Peroperative multilevel SSEP has a high specificity in detecting spinal cord ischemia but does not identify all patients with a postoperative vulnerable spinal cord. Biochemical markers in CSF increase too late for intraoperative monitoring but GFAp is promising for identifying patients at risk for postoperative delayed paraplegia.