Postoperative cognitive decline remains a common and clinically significant complication among geriatric patients undergoing major abdominal cancer surgery. Age-related physiological vulnerability, impaired cerebral autoregulation, and perioperative hemodynamic instability contribute to the development of postoperative neurocognitive impairment.

Goal-directed fluid therapy (GDFT), guided by dynamic hemodynamic parameters, has been proposed as an individualized approach to optimize tissue perfusion while avoiding both hypovolemia and fluid overload. Non-invasive monitoring technologies, such as pleth variability index (PVI) and perfusion index (PI), allow continuous assessment of fluid responsiveness without the risks associated with invasive monitoring, making them particularly suitable for elderly surgical populations.

This prospective observational cohort study aims to evaluate the association between intraoperative PVI/PI-guided GDFT and postoperative cognitive outcomes in geriatric patients undergoing elective major abdominal cancer surgery. Patients are managed according to routine clinical practice, either with individualized GDFT or conventional fluid therapy, as determined by the attending anesthesiologist.

The primary outcome is the change in cognitive function, assessed using Mini-Mental State Examination (MMSE) scores from baseline to postoperative day 1 and postoperative day 7. Longitudinal changes in cognitive function will be analyzed using adjusted statistical models to account for repeated measurements over time and potential confounding factors, including age, ASA physical status, duration of surgery, and intraoperative blood loss.

Secondary outcomes include intraoperative fluid administration, hemodynamic parameters, estimated blood loss, and net fluid balance. The study is designed to provide clinically relevant evidence on whether individualized, non-invasive hemodynamic monitoring strategies are associated with improved perioperative physiological stability and early postoperative cognitive recovery in elderly surgical patients.

Postoperative neurocognitive disorders, including early postoperative cognitive decline, represent a significant source of morbidity in geriatric patients undergoing major abdominal cancer surgery. These impairments are multifactorial and are thought to arise from the interaction of perioperative hemodynamic instability, impaired cerebral autoregulation, systemic inflammatory responses, and age-related reductions in physiological reserve.

Among perioperative factors, intraoperative fluid management plays a central role in maintaining adequate tissue perfusion and organ function. Both hypovolemia and fluid overload have been associated with adverse outcomes, including impaired microcirculatory perfusion and potential effects on cerebral oxygen delivery. Traditional fluid management strategies, typically based on fixed formulas and static physiological parameters, may not adequately reflect inter-individual variability, particularly in elderly patients with altered cardiovascular compliance and limited adaptive capacity.

Goal-directed fluid therapy (GDFT) has emerged as an individualized hemodynamic management strategy aimed at optimizing stroke volume and tissue perfusion through the use of dynamic indicators of fluid responsiveness. While randomized trials and meta-analyses have demonstrated that GDFT can improve perioperative outcomes such as complication rates and length of hospital stay, its impact on postoperative cognitive outcomes remains insufficiently characterized, especially in oncologic geriatric populations.

Recent advances in non-invasive hemodynamic monitoring technologies, including the use of pleth variability index (PVI) and perfusion index (PI), allow continuous assessment of fluid responsiveness without the need for invasive cardiac output monitoring. These tools offer a practical and safer alternative in routine clinical practice, particularly in elderly patients where invasive monitoring may not always be feasible.

This study is designed as a prospective observational cohort study conducted in geriatric patients undergoing elective major abdominal cancer surgery. Patients are managed according to standard clinical practice, and intraoperative fluid management strategy-either PVI/PI-guided GDFT or conventional fluid therapy-is determined by the attending anesthesiologist. No intervention is assigned by the study protocol, and no modification of routine clinical care is performed.

The primary objective of the study is to evaluate the association between intraoperative fluid management strategy and postoperative cognitive trajectory. Cognitive function is assessed using the Mini-Mental State Examination (MMSE) at three time points: preoperatively (baseline), postoperative day 1, and postoperative day 7. The primary outcome is defined as the change in MMSE scores over time.

To appropriately account for repeated cognitive measurements and potential confounding, longitudinal statistical models will be employed. Specifically, mixed-effects modeling will be used to evaluate the interaction between time and fluid management strategy, while adjusting for clinically relevant covariates, including age, ASA physical status, duration of surgery, and intraoperative blood loss.

Secondary objectives include evaluating the association between fluid management strategy and intraoperative physiological parameters, including total fluid administered, mean arterial pressure, heart rate, estimated blood loss, and net fluid balance.

Given the observational nature of the study, results will be interpreted as associations rather than causal effects. The study aims to generate clinically relevant evidence regarding whether individualized, non-invasive, goal-directed fluid strategies are associated with improved early postoperative cognitive recovery and optimized perioperative physiological stability in geriatric surgical patients.

Inclusion Criteria:

• Age ≥ 65 years (geriatric patients)
• Scheduled for elective major abdominal cancer surgery
• American Society of Anesthesiologists (ASA) Physical Status I-IV
• Eastern Cooperative Oncology Group (ECOG/WHO/Zubrod) performance status ≥ 2
• Ability to complete cognitive assessments
• Provision of written informed consent

Exclusion Criteria:

• Severe cardiac dysfunction (Cardiac Index ≤ 2.2 L/min/m²)
• History of neurological or psychiatric disorders (e.g., dementia, Alzheimer's disease)
• Use of medications that significantly affect cognitive function
• Severe hepatic or renal failure
• Prior chemotherapy or radiotherapy before surgery
• Intraoperative or perioperative blood transfusion
• Prolonged mechanical ventilation (inability to extubate immediately after surgery)
• Pre-existing cognitive impairment (baseline Mini-Mental State Examination [MMSE] score < 24)

The study population consists of geriatric patients (aged 65 and older) scheduled for elective major abdominal cancer surgery at the University of Health Sciences, Dr. Abdurrahman Yurtaslan Ankara Oncology Training and Research Hospital. Participants will be selected from patients who meet the inclusion criteria and provide informed consent during their preoperative evaluation in the anesthesiology clinic

Individual participant data (IPD) will not be shared to ensure patient confidentiality and data privacy, as per the ethical committee approval and institutional policies. Only aggregated study results will be published.