Minimal-flow Anesthesia and Cognitive Outcomes in Elderly Surgical Patients

Purpose: Postoperative cognitive dysfunction (POCD) is a common complication in elderly patients following major surgery and is associated with impaired attention, memory, and executive functions. Advanced age and prolonged surgical duration are among the most important risk factors. Minimal flow anesthesia has been suggested to reduce postoperative cognitive impairment by providing more stable anesthetic depth and reducing physiological stress. The aim of this study is to investigate the relationship between surgical duration and postoperative cognitive dysfunction in elderly patients undergoing surgery under minimal flow anesthesia.

Detailed Description: Postoperative cognitive dysfunction (POCD) is a syndrome characterized by deterioration in cognitive domains such as attention, memory, executive function, and psychomotor speed, particularly in elderly patients after major surgical procedures. POCD may become evident in the early postoperative hours or may present days to weeks after surgery. Its incidence increases with age, prolonged surgical duration, anesthetic technique, comorbid conditions, and perioperative physiological disturbances. Diagnosis of POCD requires comparison of preoperative baseline cognitive status with postoperative neurocognitive assessments. The Mini-Mental State Examination (MMSE) and the Richmond Agitation-Sedation Scale (RASS) are validated and reliable tools for evaluating cognitive status in the perioperative period. Minimal flow anesthesia is defined as the use of fresh gas flow rates between 0.25 and 0.5 L/min, allowing partial rebreathing of anesthetic agents. This technique reduces anesthetic consumption, maintains stable anesthetic depth, and preserves temperature and humidity, potentially minimizing physiological stress. Previous studies suggest that minimal flow anesthesia with sevoflurane may be associated with a lower incidence of early postoperative cognitive impairment compared to higher flow techniques. In this prospective interventional study, patients aged 65-85 years undergoing surgery under minimal flow inhalational anesthesia will be enrolled. Patients will be divided into two groups based on surgical duration: surgeries lasting less than 2 hours and surgeries lasting 2 hours or longer, with 45 patients in each group. All patients will undergo preoperative cognitive assessment using the MMSE. Standard ASA monitoring and bispectral index (BIS) monitoring will be applied intraoperatively to maintain anesthetic depth between BIS values of 40 and 60. Anesthesia induction and maintenance will be performed using routine anesthetic agents and minimal flow inhalational anesthesia as part of standard clinical practice. Neuromuscular blockade will be reversed with sugammadex at the end of surgery. Postoperatively, patients will be evaluated using the RASS at the 10th, 30th, and 60th minutes in the recovery room. Neurology consultation will be requested for patients with RASS scores outside the normal range. Vital signs, pain scores (VAS), and blood glucose levels will be recorded during these assessments. Postoperative cognitive function will be reassessed using the MMSE at 24 hours and on postoperative day 7. Preoperative and postoperative cognitive assessments will be conducted by study investigators who are blinded to surgical duration. The anesthetic management will be performed by anesthesiologists not involved in the study. The primary objective of this study is to evaluate the association between surgical duration and postoperative cognitive dysfunction in elderly patients undergoing surgery under minimal flow anesthesia.