The use of electrophysiological monitoring in the intraoperative management of intracranial aneurysms

Objectives-Somatosensory evoked potentials (SSEPs) and brainstem auditory e voked potentials (BAEPs) have been increasingly utilised during surgery for intracranial aneurysms to identify cerebral ischaemia. Between July 1994 a nd April 1996, we surgically treated 70 aneurysms in 49 consecutive patient s (58 operations) with the aid of intraoperative evoked potential monitorin g. This study sought to evaluate the usefulness of SSEP and BAEP monitoring during intracranial aneurysm surgery. Methods-Mean patient age was 51.9 (range 18-79) years. The sizes of the ane urysms were 3-4 mm (15), 5-9 mm (26), 10-14 mm (11), 15-19 mm (seven), 20-2 4 mm (six), and >25 mm (five). SSEPs were monitored in 58 procedures (100%) and BAEPs in 15 (26%). The neurological status of the patients was evaluat ed before and after surgery. Results-Thirteen of the 58 procedures (22%) monitored with SSEPs had SSEP c hanges (12 transient, one persistent); 45 (78%) had no SSEP changes. Three of 15 patients (20%) monitored with BAEPs had changes (two transient, one p ersistent); 12 (80%) had no BAEP changes. Of the 14 patients with transient SSEP or BAEP changes, these changes resolved with adjustment or removal of aneurysm clips (nine), elevating MAP (four), or retractor adjustment (one) . Mean time from precipitating event to electrophysiological change was 8.9 minutes (range 3-32), and the mean time for recovery of potentials in pati ents with transient changes was 20.2 minutes (range 3-60). Clinical outcome was excellent in 39 patients, good in five, and poor in three (two patient s died), and was largely related to pretreatment grade. Conclusions-SSEPs and BAEPs are useful in preventing clinical neurological injury during surgery for intracranial aneurysms and in predicting which pa tients will have unfavourable outcomes.