Somatosensory evoked potentials (SSEP) are commonly used to monitor cerebral activity during intracranial aneurysm surgery. Temporary arterial occlusion is sometimes necessary and brain physiological response is heterogeneous and highly dependent to patient's physiological conditions and vascular anatomy. The aim of this study was to analyse the relation between baseline SSEP and brain physiological sensitivity to arterial temporary occlusion.

Eighty cases undergoing elective or urgent intracranial aneurysm surgery were monitored using SSEP monitoring. Aneurysms were either located on the middle cerebral artery (63.8%), the anterior cerebral artery complex (25%), the posterior communicating artery departure (8.8%) or located elsewhere (2.5%). Bilateral baseline and intraoperative SSEP were recorded. Comparison between groups was performed using Pearson Chi² test. A statistical significant level of P<0.05 was used throughout.

At the beginning of the surgery, baseline SSEP were abnormal (i.e. asymmetrical) in 27 (33.8%) cases (asy group) and normal in 53 (66.3%) cases (sym group). During intraoperative arterial temporary occlusion, no significant difference in SSEP reduction between these two groups could be observed (asy: 18/27; sym: 25/53, P=0.98). However, the proportion of SSEP recovery in the asy group (8/18) was significantly lower than in the sym group (19/25) (P=0.04).

Our study suggests that, based on initial measurement only, baseline SSEP asymmetry is associated with impaired SSEP recovery after arterial temporary occlusion and cerebral hypoperfusion. Temporary clipping should be minimized in patients with baseline SSEP asymmetry. Future search should concentrate on the correlation between these electrophysiology findings and their clinical repercussion.