Carotid endarterectomy (CEA) is the recommended treatment for symptomatic high degree stenosis of the internal carotid artery (ICA). ICA obstruction is often associated with an impaired cerebral autoregulation, implicating that cerebral perfusion pressure becomes dependent on systemic blood pressure. Therefore, to maintain cerebral perfusion pressure in this type of patients intraoperative hypotension needs to be avoided. Different short-acting agents such as phenylephrine, (a drug with vasoconstrictive properties), or ephedrine (a drug with vasoconstrictive properties combined with an increase in heart rate) can be used to correct intra-operative hypotension. In healthy subjects these agents affect the cerebral perfusion differently despite an identical effect on the systemic blood pressure. Cerebral perfusion decreases after phenylephrine administration while it is preserved after the use of ephedrine. The optimal agent for correcting hypotension in CEA patients, and thus in a situation of an impaired cerebral autoregulation, is unknown.

Therefore, the investigators propose to perform a prospective study observing the effect of phenylephrine and ephedrine on cerebral perfusion to make a recommendation regarding the use of either phenylephrine or ephedrine during CEA.

Inclusion criteria:

1. All patients undergoing CEA in the University Medical Centre Utrecht and having an appropriate temporal bone window for reliable perioperative TCD monitoring could be included.
2. All patients must have given written informed consent.

Exclusion criteria:

1. Not having a temporal bone window appropriate for TCD measurement
2. Not willing to give informed consent.
3. If the effect on BP of the given agents is insufficient (if relative hypotension persists five minutes after administration).