The monitoring of somatosensory evoked potentials and neurologic complications in aneurysm surgery

Somatosensory evoked potential (SSEP) changes during cerebral aneurysm surgery and their relationship to post operative neurologic complications have been studied on many occasions. However, it is still a matter of debate whether SSEP monitoring is really helpful in detecting or preventing neurologic complications. We studied 87 patients undergoing aneurysm surgery of the anterior cerebral circulation and SSEPs were monitored in 60 of these patients. All patients were grade 2 by the subarachnoid hemorrhage (SAH) grading system. Median nerve SSEP was monitored for middle cerebral or internal carotid artery aneurysms and posterior tibial nerve: SSEP for anterior cerebral artery aneurysms. A decrease in the cortical amplitude of more than 50%, compared with control, was considered significant and interventions were then taken to reverse the SSEP. The pre- and postoperative neurologic deficits of each patient were evaluated immediately before and after surgery. No significant difference was found in the incidence of postoperative neurologic complications in the SSEP monitored (15% [9/60]) and unmonitored patients (22% [6/27]). In the SSEP monitored patients, the amplitudes of SSEPs decreased significantly in 14 patients and 4 of these showed neurologic complications. However, SSEP amplitudes were not significantly changed in 46 patients, and 5 of these showed neurologic complications. Significant changes in the amplitude of SSEP might represent neuronal injury, but the absence of change in the SSEP cannot guarantee patient safety. Our results suggest that SSEP monitoring may be useful for detecting the danger of neuronal injury, but that it does not reduce the incidence of neurologic complications in aneurysm surgery.