Intraoperative SSEP Monitoring during Aneurysm Surgery

Somatosensory evoked potential(SSEP) has been recorded during 31 operations for intracranial aneurysm. We had monitored the SSEP in each stage of aneurysm surgery(preoperative, anesthetic induction, dura opening, temporary vascular occlusion, aneurysm neck clipping and 30 minute after aneurysm neck clipping). Temporary occlusion of intracranial arteries have performed in 21 cases. In cortical amplitude of more than 50% as compared with induction was considered to be "significant" SSEP change. Eleven out of 21 cases of temporary vascular occlusion showed significant decrease of amplitude. Three out of 4 cases with flat wave had new neurologic deficits postoperatively. We studied the relationship between SSEP changes and postoperative neurologic deficit and concluded as follows: 1) The monitoring of amplitude of SSEP may help control the duration and number of application in temporary clipping during aneurysm surgery. 2) Decreased in amplitude with temporary clipping, especially flat wave, is a strong suggestion of the postoperative neurologic deficit. These results indicate that monitoring of SSEP during aneurysm surgery would be helpful to reduce the incidence of postoperative neurologic deficits.

The Findings of Brainstem Auditory Evoked Pontential(BAEP) and Somatosensory Evoked Potential(SSEP) in Head Injury

There were 84 cases of brainstem auditory evoked potential(BAEP) and 90 cases of somatosensory evoked potential(SSEP) from the 124 cases of head injury. The studies were performed within the first three days after head injury in most cases and after ten days in emergency operative cases. The results of BAEP and SSEP studies recorded from 67 normal volunteers were used as a control group. The latency, amplitude and wave pattern of the evoked potential were examined and a peak or interpeak latency were considered abnormal when it exceeded the corresponding mean(2SD found in the control group. The wave patterns were arranged in BAEP as grade I:all waves were normal; grade II: waves I, II, III were abnormal;grade III:waves IV, V, VI were abnormal;grade IV:all waves were abnormal. In SSEP as grade I:all waves were normal;grade II:N13 wave was abnormal;grade III:N19wave was abnormal;grade IV:all waves were abnormal. The abnormal findings by percentage were:47.6% in latency of BAEP, 68.9% in latency of SSEP, 49.4% in wave pattern of BAEP and 87.8% in wave pattern of SSEP. The BAEP was superior to SSEP in correlation to clinical parameters including GCS, duration of coma, basal cisterns in initial brain CT scan and Glasgow outcome scale(GOS). As a BAEP criterion, the wave V latency and the BCT(III-V interpeak latency) and as a SSEP criterion, the central conduction time(N19-N13) were more correlated to duration of coma and GOS. The appearance of the basal cisterns on initial brain CT is significantly correlated with wave V and BCT of BAEP only. Grade I and II were reliable predictors of a good prognosis. Therefore, we concluded that BAEP and SSEP are adjunctively diagnostic tests for determining the outcome of head injuried patients.