Memory During Inhalation Anesthesia Performed With or Without Bispectral Index (BIS) in Patients Undergoing Thyroidectomy

The purpose of this study is 1) to investigate whether the use of BIS as a guide to the administration of inhaled anesthetic (sevoflurane or desflurane) compared with the use of hemodynamic parameters (blood pressure and heart rate) would affect the occurrence of implicit memory and /or dreams recall and 2) to check whether the occurrence of implicit memory and/or dreams recall is related with MAC (Minimal Alveolar Concentration) of inhalational anesthetics and/or preoperative anxiety levels.