The Effect of Intravenous Versus Volatile Anesthesia on Postoperative Cognitive Dysfunction in Elderly Patients

The goal of this clinical trial is to compare the permeability of blood-brain barrier between the intravenous anesthesia group and the inhalation gas anesthesia group in the elderly patients undergoing surgery. The main questions it aims to answer are: * \[Is the permeability of blood-brain barrier between the intravenous anesthesia group and the inhalation gas anesthesia group in the elderly patients different?\] * \[Is the incidence of postoperative cognitive dysfunction between the intravenous anesthesia group and the inhalation gas anesthesia group different?\] Participants will be anesthetized with different categories of anesthetics. * Intravenous anesthetics * Inhalation gas anesthetics