Transcranial Doppler measurement before and after carotid endarterectomy.

Carotid endarterectomy not only removes a source of emboli but significantly increases flow up the internal carotid artery (ICA). ICA flow and middle cerebral artery velocity (Vmca) measurements were made before, during and after endarterectomy in 40 consecutive patients. Mean ICA flow increased from 207 ml/min (95% confidence interval (CI) 136-259) to 388 ml/min (95% CI 348-428) (P < 0.001, Mann-Whitney U test) following endarterectomy. Despite this, Vmca did not rise significantly at the end of the procedure. By the first postoperative day Vmca rose to 55.3 cm/s (95% CI 47.6-62.4) (P < 0.025, ANOVA) only to fall preoperative values (46.0 cm/s (95% CI 40.0-52.1)) by 6 weeks. These results suggest that cerebral autoregulation takes time to adapt to the increased flow and pressure following endarterectomy, but has stabilized by 6 weeks.