Inclusion Criteria:  undergo a total thyroidectomy operation ASA I-II euthyroid patients in the preoperative period  Exclusion Criteria:  Hemoglobin< 8 g / dl Hypertension Hyperlipidemia Pregnancy Patients diagnosed with diabetes mellitus Cerebrovascular insufficiency Known carotid artery lesion Metabolic diseases Any intracranial pathology present Surgeries exceeding 180 minutes