Value of the Time-Weighted Average (TWA) of Mean Arterial Pressure (MAP) and Cerebral Oximetry (rSO₂) as Predictors of Postoperative Tissue Perfusion Impairment in Patients Undergoing Cardiac Surgery

Overview

Neurological problems after heart surgery are common and include confusion, memory loss, and difficulty thinking clearly. These issues may appear hours or days after surgery and can negatively affect recovery. During heart surgery, blood flow and oxygen delivery to the brain may decrease, causing changes in blood pressure and cerebral oxygenation. Previous studies suggest that prolonged drops in mean arterial pressure (MAP) or cerebral oxygenation (rSO₂) are linked to worse postoperative outcomes. Continuous monitoring of blood pressure and cerebral oxygenation is standard in cardiac surgery. This study aims to evaluate the duration and severity of intraoperative drops in MAP and cerebral oxygenation. These measures may provide a more accurate assessment of neurological risk than isolated measurements. The primary objective is to determine whether decreases in MAP and cerebral oxygenation, as well as their duration and intensity during surgery, are associated with postoperative neurological complications. This is a prospective, observational study in adult patients undergoing cardiac surgery, with or without cardiopulmonary bypass (CPB). CPB diverts blood through a machine that performs the work of the heart and lungs while the heart is operated on. All patients will receive standard monitoring, including continuous MAP and cerebral oxygenation measurements. No additional interventions will be performed. Neurological status will be assessed using validated clinical scales before and after surgery. Other outcomes include kidney function, ICU and hospital stay length, postoperative complications, and in-hospital mortality. Validating these measures as a predictive tool could enable early identification of patients at higher risk of neurological injury and allow more individualized intraoperative management to reduce morbidity, hospital stay, and healthcare costs.

Postoperative neurocognitive dysfunction (PND), which includes postoperative delirium (POD) and postoperative cognitive dysfunction (POCD), is a frequent complication in patients undergoing cardiac surgery, with reported incidences of 14-35% for POD and up to 80% for POCD. Both conditions have been associated with prolonged intensive care unit (ICU) and hospital stays, long-term cognitive decline, and increased mortality. POD is defined by the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), as an acute and fluctuating disturbance of attention and awareness, accompanied by cognitive or perceptual changes, typically occurring in the first days after surgery. The most commonly used assessment tool is the Confusion Assessment Method for the ICU (CAM-ICU), which demonstrates high sensitivity and specificity and is suitable for intubated patients or those in critical care. POCD is considered a persistent reduction in cognitive function, particularly memory, attention, processing speed, and executive functions. It usually appears after the first postoperative week and can last from weeks to months, being more common in older adults. The Mini Mental State Exam (MMSE) is recommended as a screening and predictive tool for POCD. There is evidence that significant decreases in cerebral oxygen saturation (rSO₂), measured non-invasively by near-infrared spectroscopy (NIRS) (either a drop \>20% from baseline or absolute values \<50%), are associated with higher rates of postoperative neurocognitive dysfunction. Prolonged intraoperative hypotension, defined as mean arterial pressure (MAP) \<65 mmHg, is also linked to worse postoperative neurological outcomes. Several studies have compared whether rSO₂ or MAP better detect postoperative neurocognitive dysfunction, with some showing that rSO₂ is a more sensitive predictor, reflecting global perfusion and immediate prognosis. Clinical practice guidelines recommend monitoring rSO₂ to improve neurological outcomes after cardiac surgery. Decreases in rSO₂ can indicate microcirculatory dysfunction even when blood pressure appears normal, correlating with adverse clinical outcomes such as elevated lactate, acute kidney injury, prolonged mechanical ventilation, or extended vasopressor use. The time-weighted average (TWA) allows quantification not only of the magnitude but also the duration of hemodynamic or hypoxic deviations. TWA is calculated as: TWA = ∑ (depth of deviation × duration in minutes) / total procedure duration For TWA-MAP, the depth is the number of mmHg below 65 mmHg, multiplied by the duration, and adjusted to the total procedure time. The same principle applies to TWA-rSO₂. Elevated TWA-MAP indicates macrohemodynamic dysfunction, whereas elevated TWA-rSO₂ reflects cerebral microcirculatory dysfunction. Previous studies have correlated TWA-MAP with acute kidney injury, ICU stay, and mortality. TWA-rSO₂ has been used in observational studies and correlated with lactate levels, creatinine, or duration of vasopressor therapy. However, no studies have evaluated the predictive value of TWA-MAP and TWA-rSO₂ for postoperative neurocognitive dysfunction (delirium or cognitive impairment) after cardiac surgery. Critical gaps remain in establishing validated TWA thresholds for predicting brain injury, determining whether neurological impairment develops beyond the intraoperative period, and evaluating the diagnostic sensitivity and specificity of this tool.