The Effect of Positive End-Expiratory Pressure Levels on Perfusion Index and Neurocognitive Functions in Geriatric Patients

Overview

With the increasing geriatric population, age-related physiological changes and common comorbidities increase the risk of surgical and anesthesia-related complications in this patient group. Therefore, careful planning of anesthesia management and ventilation strategies is crucial to achieve safe and successful clinical outcomes. Positive end-expiratory pressure (PEEP), one of these strategies, should be applied with careful consideration of the balance between ensuring oxygenation and maintaining cardiovascular stability in geriatric patients. Early detection of hypoperfusion during the intraoperative period is also an important part of perioperative management. To this end, near-infrared spectroscopy (NIRS) is used as a noninvasive monitoring method to assess cerebral oxygenation, while the perfusion index (PI) is used to evaluate peripheral circulation, providing clinicians with valuable information for predicting potential complications. However, one of the most important neurological complications that can occur after surgery in geriatric patients is postoperative cognitive dysfunction (POCD). The Mini-Mental State Examination (MMSE) is widely preferred for assessing cognitive function during the perioperative period due to its ease of application and reliability. The primary objective of this study is to investigate the effects of different PEEP levels on PI in geriatric patients undergoing laparoscopic cholecystectomy and to reveal changes in neurocognitive function by comparing preoperative and postoperative MMSE scores. Our secondary objectives are to evaluate the effects of PEEP on NIRS values and to analyze the possible relationships between NIRS, PI, hemodynamic parameters, and MMSE scores.

This study was conducted at the General Surgery Operating Room of Ankara Bilkent City Hospital, Ministry of Health, Turkey, with a total of 78 patients aged 65 years and older who were scheduled to undergo elective laparoscopic cholecystectomy. The study was designed as a prospective randomized controlled trial. Using a computer-assisted randomization method, the 78 patients were divided into three groups. Group 5 was ventilated with 5 cmH₂O PEEP, Group 7 with 7 cmH₂O PEEP, and Group 9 with 9 cmH₂O PEEP. On the day of surgery, patients' age, gender, height, weight, body mass index (BMI), comorbidities, medications taken regularly, surgical history, and education level were recorded using a standardized data form in the preoperative waiting area. The Mini Mental State Examination (MMSE) was administered to all patients 2 hours before surgery. After patients were taken to the operating room, noninvasive arterial blood pressure, electrocardiography (ECG), and pulse oximetry were performed as part of standard monitoring. Additionally, four-channel frontal EEG-based SedLine® (Patient State Index, PSI; Masimo Corporation, Irvine, CA, USA) monitoring was used to monitor anesthesia depth, and NIRS (O3® regional oximetry, Masimo Corporation, Irvine, CA, USA) monitoring was used to assess cerebral oxygenation. After cleaning the forehead area with an appropriate antiseptic, the SedLine® PSI electrode and O3® NIRS sensors were placed, and baseline values were recorded. For peripheral perfusion monitoring, the PI probe (Masimo Rainbow® Pulse CO-Oximetry, Masimo Corporation, Irvine, CA, USA) was placed on the third finger of the hand without the noninvasive blood pressure cuff. The hand was wrapped to reduce optical interference from ambient light and maintain thermal equilibrium. Before anesthesia induction, 3 minutes of preoxygenation was administered with 100% oxygen via a balloon mask. Anesthesia induction was then performed with fentanyl (2 mcg/kg), lidocaine (1 mg/kg), propofol (2 mg/kg), and rocuronium (0.6 mg/kg); midazolam was not administered. After achieving adequate depth of anesthesia, an endotracheal tube of appropriate size was placed in the patient. Ventilator settings were adjusted to a 50:50 oxygen-air mixture and a fresh gas flow of 2 L/min, targeting a tidal volume of 6-8 mL/kg based on ideal body weight and maintaining EtCO₂ within the range of 35-45 mmHg. PEEP was applied at a level determined by randomization in each patient. Anesthesia maintenance was achieved with sevoflurane and remifentanil infusion (0.01-0.1 mcg/kg/min) to maintain a target PSI range of 25-50. An orogastric tube was placed for gastric decompression. The surgical procedure was performed using the standard laparoscopic cholecystectomy technique. Pneumoperitoneum pressure was adjusted and maintained at 10-12 mmHg; the operating table was positioned at approximately 30° reverse Trendelenburg. Operating room temperature was maintained at 18-20 °C. Parameters evaluated (SAP, DAP, MAP, heart rate, SpO₂, PI, PSI, NIRS left and right) before and after anesthesia induction; after intubation; before pneumoperitoneum and at 1, 5, 10, 15, 30, 45, and 60 minutes after the start of pneumoperitoneum; every 30 minutes thereafter; and also at the end of pneumoperitoneum, at the end of surgery, and after extubation. Additionally, the hemoglobin levels at admission and discharge, the total amount of fluid administered, and the duration of anesthesia and surgery were also recorded. For postoperative pain management, patients received standard tramadol 1 mg/kg IV and paracetamol 1 g IV after gallbladder removal. Following the operation, 2 mg/kg sugammadex IV was administered, and patients were extubated once they began spontaneous breathing. After recovery in the operating room, patients were transferred to the postoperative recovery room. On postoperative day 1, patients underwent the MMSE test, and the results were recorded. Additionally, if any complications developed during the postoperative period, this was noted.