Effect of PEEP on Cardiac Function

The purpose of this single-center, prospective study is to evaluate the physiologic effect of changes in PEEP on biventricular mechanics and RV-pulmonary arterial (RV-PA) coupling in adult patients undergoing cardiac surgery.

Inclusion Criteria: * 1\. Age ≥ 18 years * 2\. Scheduled to undergo cardiac surgery requiring general anesthesia * 3\. Planned use of intraoperative transesophageal echocardiography (TEE) as part of routine clinical care * 4\. Planned placement of a pulmonary artery catheter as part of clinical care (Pulmonary artery catheter placement will be performed solely based on clinical judgment by the treating anesthesia and surgical teams. At our institution, pulmonary artery catheters are routinely placed in cardiac surgery patients with clinical indications including: * preoperative pulmonary hypertension (e.g., estimated PCWP \>20 mmHg or elevated filling pressures on preoperative echocardiography), * right ventricular dysfunction or suspected RV failure (preoperative visual TTE assessment), * significant cardiopulmonary comorbidity, * or anticipated complex, prolonged, or high-acuity cardiac surgery. The research team will not influence decisions regarding catheter placement. Only patients already scheduled to receive a clinically indicated pulmonary artery catheter will be eligible for enrollment.) * 5\. Able and willing to provide written informed consent prior to surgery Exclusion Criteria: * 1\. Significant arrhythmia (e.g., atrial fibrillation with uncontrolled ventricular response or other rhythm disturbances) that would interfere with reliable pressure waveform or echocardiographic measurements. * 2\. Severe valvular disease where protocol-related PEEP changes may pose unacceptable hemodynamic risk, as determined by the clinical team. * 3\. Significant chronic lung disease or other pulmonary pathology where PEEP adjustments may be unsafe (e.g., severe COPD with dynamic hyperinflation, bullous lung disease), at the discretion of the anesthesia team. * 4\. Contraindication to changes in PEEP, including inability to tolerate the planned PEEP titration due to hemodynamic instability or clinician concern. * 5\. Any contraindication to TEE (if clinically required TEE is not performed or is contraindicated, the subject will not be eligible) * 6\. Investigator or clinical team discretion (e.g., safety concerns, inability to obtain reliable measurements, or conflict with other perioperative research protocols)