BACKGROUND: Intravenous and inhalational anesthetic agents have differing effects on cerebral hemodynamics: Sevoflurane causes some vasodilation, whereas propofol does not. The authors hypothesized that these differences affect internal carotid artery pressure (ICAP) and the apparent zero flow pressure (critical closing pressure) during carotid endarterectomy. Vasodilation is expected to increase blood flow, reduce ICAP, and reduce apparent zero flow pressure. METHODS: In a randomized crossover study, the gradient between systemic arterial pressure and ICAP during carotid clamping was measured while changing between sevoflurane and propofol in 32 patients. Middle cerebral artery blood velocity, recorded by transcranial Doppler, and ICAP waveforms were analyzed to determine the apparent zero flow pressure. RESULTS: ICAP increased when changing from sevoflurane to propofol, causing the mean gradient between arterial pressure and ICAP to decrease by 10 mmHg (95% confidence interval, 6-14 mmHg; P < 0.0001). Changing from propofol to sevoflurane had the opposite effect: The pressure gradient increased by 5 mmHg (95% confidence interval, 2-7 mmHg; P = 0.002). Ipsilateral middle cerebral artery blood velocity decreased when changing from sevoflurane to propofol. Cerebral steal was detected in one patient after changing from propofol to sevoflurane. The apparent zero flow pressure (mean ± SD) was 22 ± 10 mmHg with sevoflurane and 30 ± 14 mmHg with propofol (P < 0.01). There was incomplete drug crossover due to the limited duration of carotid clamping. CONCLUSIONS: Compared with sevoflurane, ipsilateral ICAP and apparent zero flow pressure are both higher with propofol. Vasodilatation associated with sevoflurane can cause cerebral steal.