Intraoperative cerebral monitoring in carotid surgery

We have used and studied intraoperative cerebral monitoring in order to prevent intraoperative and early postoperative cerebral ischaemia. The techniques examined have included stump pressure measurement, the evaluation of somatosensory evoked potentials (SEPs) and completion intraoperative angiography. Stump pressure was measured in 920 patients and a safety level of 50 mmHg confirmed. Below this value, non-shunted patients were three times more likely to have cerebrovascular accident (CVA). SEPs were prospectively monitored in 72 patients and a mean decrease of N20-P25 in complex amplitude was seen in patients with a positive CT scan. In particular, pathological SEPs were found in 53% of patients with a positive CT scan, and in 54% of those with a contralateral carotid occlusion. In these patients, the N20-P25 amplitude fell progressively in the first 4 min. Using SEPs, the indication for shunting was 42% lower than with the measurement of back pressure and no patient with normal SEPs had a postoperative neurological deficit. The data obtained under local anaesthesia in 25 patients monitored by stump pressure and SEPs did not give better results. Intraoperative completion angiography performed routinely since 1978 has made it possible to reduce the need for immediate reoperation from 10-2%.