FACTORS INFLUENCING THE HYPEREMIC RESPONSE AFTER CAROTID ENDARTERECTOMY

Transcranial Doppler ultrasonography was used to evaluate serially the changes in middle cerebral artery blood flow velocity (MCAV) in 37 co nsecutive patients during the first 72h after carotid endarterectomy t o identify factors that may predispose towards postoperative hyperaemi a. Within 6h of endarterectomy, median MCAV in the operated hemisphere was 48 per cent (95 per cent confidence interval 37-60 per cent) abov e that on admission and remained 27 per cent (95 per cent confidence i nterval 19-37 per cent) higher at 72 h. There was a similar, but less marked, increase in MCAV in the contralateral middle cerebral artery d uring the same time period. There was no association between the posto perative increase in MCAV and clinical presentation, admission MCAV, t he presence or absence of a residual neurological deficit or infarctio n on computed tomography before operation, carotid clamp time, shunt u sage, internal carotid artery stump pressure or MCAV during clamping. The greatest increase in MCAV was observed in patients with internal c arotid artery stenosis greater than or equal to 50 per cent and, more particularly, in those with preoperative evidence of impaired cerebrov ascular reserve. In the latter patients, MCAV was 100 per cent above t he admission level within 12h of operation and was still 50 per cent r aised at 72 h.