The relationship between evoked potentials and measurements of S-100 protein in cerebrospinal fluid during and after thoracoabdominal aortic aneurysm surgery

Objective: This study was performed to correlate the changes in concentration of S-100 protein in the cerebrospinal fluid (CSF) during and after thoracoabdominal aortic aneurysm (TAAA) surgery with the results of somatosensory and motor evoked potential monitoring. Methods: The study was designed as a prospective study at St Antonius Hospital in Nieuwegein, The Netherlands. The participants were 19 patients who were undergoing elective TAAA surgery. CSP samples for analysis of S-100 protein were drawn after the induction of anesthesia, during the cross-clamp period of the critical aortic segment, after 5 minutes of reperfusion of this segment, during the closure of the skin, and 24 hours after the closure of the skin. In all the patients, continuous intraoperative recording of myogenic motor potentials evoked by transcranial electrical stimulation (tcMEP) and somatosensory potentials evoked by stimulation of the postetior tibial nerve took place to monitor the integrity of the spinal cord. The operative technique consisted of staged or sequential clamping to maximize the beneficial effect of the distal perfusion by the left heart bypass, continuous CSP drainage to keep the CSF pressure below 10 mm Hg, and moderate hypothermia (32 degrees C rectal temperature). We correlated the measured concentrations of S-100 protein in CSF with the results of evoked potential monitoring during surgery and the number of intercostals reimplanted and oversewn. Results: In all the patients, the concentration of S-100 protein was increased in CSF The highest concentration of S-100 protein was found in the CSF sample taken 5 minutes after reperfusion of the critical aortic segment. There was a good (negative) correlation between the changes in 5-100 protein in CSF and the changes in motor evoked potential monitoring during the cross-damp period. The best (negative) correlation was detected between the S-100 protein elevation in the CSP sample drawn 5 minutes after reperfusion and the tcMEP amplitude reduction during clamping (r = -0.73; P = .007). No relation was found between the S-100 protein dynamics in CSF and somatosensory evoked potential monitoring. A positive (r = 0.58; P = .05) correlation was found between the change in tcMEP amplitude during clamping and the number of reattached intercostals. A moderate to good (r = -0.5 to -0.7; P < .05) correlation between the number of reattached intecostals and the changes in 5-100 protein concentration in CSF during TAAA surgery was found. Our data show that transient elevations in S-100 protein after cross clamping are larger in those patients with marked decrease in tcMEP from baseline during the cross-clamp period. Conclusion: A correlation is shown between an increasing concentration of S-100 protein in CSF and a reduction in tcMEP amplitude during cross clamping of the aorta. The S-100 protein in CSF seems to be a marker of potential clinical value in the evaluation of the effects of procedures to detect and reduce spinal cord ischemia.