This study was a single-center, exploratory, randomized controlled trial. First, the effects of ephedrine, phenylephrine, or norepinephrine on cerebral blood flow hemodynamics in patients undergoing carotid endarterectomy were evaluated using TCD techniques to investigate the specific mechanisms of the three vasopressors on cerebral blood flow and oxygen metabolism in brain tissues.

Carotid endarterectomy is a procedure used to remove plaque from the common and internal carotid arteries and improve cerebral perfusion. Clinical studies have demonstrated the effectiveness of this procedure in both symptomatic and asymptomatic patients. intraoperative circulatory management challenges in carotid endarterectomy include the following: ① the incidence of preoperative combined coronary artery disease, hypertension and diabetes mellitus is relatively high in patients undergoing carotid endarterectomy, and there is a pathological basis for systemic vascular injury, increasing the risk of perioperative cardiovascular and cerebrovascular complications, such as myocardial ischemia and stroke. ② During the CEA procedure, the common carotid artery, internal carotid artery and external carotid artery and the superior thyroid artery need to be blocked respectively, the source of blood supply to the cerebral hemisphere on the operated side is reduced and depends only on the Willis circle supply. ③ Carotid sinus pressure receptor pull stimulation causes circulatory fluctuations. During CEA, a relatively high arterial pressure is required to provide adequate cerebral perfusion. However, achieving this target blood pressure level intraoperatively can be challenging due to given conditions, the presence of induction drugs and anesthetics. Therefore, it is particularly important to maintain cerebral hemodynamic stability and ensure tissue perfusion with intraoperative use of vasopressors.

The purpose of this study was to evaluate the effects of ephedrine, phenylephrine, or norepinephrine on cerebral blood flow hemodynamics in CEA patients using TCD techniques to investigate the specific mechanisms of the three boosting agents on cerebral blood flow and oxygen metabolism in brain tissues.

Inclusion Criteria:

1. age 40-80 years.
2. elective carotid endarterectomy.
3. Signed informed consent

Exclusion Criteria:

1. American Society of Anesthesiologists physical status classification (ASA) IV - VI.
2. renal failure (estimated glomerular filtration rate less than 60 ml/min.m2).
3. cardiac arrhythmias.
4. Allergy to ephedrine, phenylephrine or norepinephrine, gadobutrol.
5. patients with preoperative TCD suggesting poor temporal window signal.
6. patients with severe carotid artery stenosis with no flow signal detected by TCD
7. Patients with tandem lesions of carotid artery stenosis

This study could not be blinded to the treating anesthesiologists. However, blinding was maintained for the patients and the assessors of outcome indicators. Postoperative follow-up was performed by a specially trained physician who did not have access to any information about the patients' cases and subgroups.