Effect of PEEP on Cardiac Function

Positive end-expiratory pressure (PEEP) is a critical modality of mechanical ventilation but has important and often underappreciated effects on biventricular mechanics. PEEP is frequently selected based primarily on respiratory mechanics and oxygenation targets; however, increasing intrathoracic pressure may reduce RV preload by elevating right atrial pressure, while increasing transpulmonary pressure may increase RV afterload by compressing intra-alveolar pulmonary vessels and redistributing pulmonary blood flow. This is important specifically in the context of cardiac surgery where right ventricular (RV) function plays a critical role in determining postoperative morbidity and mortality. Perioperative RV dysfunction has been consistently associated with adverse outcomes, including prolonged vasopressor and inotrope requirements, difficulty weaning from cardiopulmonary bypass, longer intensive care unit stays, and increased mortality.

Right ventricular-pulmonary arterial (RV-PA) coupling provides a physiologically integrated assessment of RV performance by quantifying the relationship between RV contractility and afterload. Animal studies have shown that incremental PEEP increases can impair biventricular mechanics and precipitate RV-PA uncoupling. However, these physiologic effects have not been systematically characterized in the perioperative setting in the cardiac surgery population. This protocol seeks to address this knowledge gap by systematically evaluating biventricular mechanics and RV-PA coupling across varying PEEP levels in a controlled setting, using tools already employed in routine cardiac surgical care (pulmonary artery catheter and intraoperative TEE).

The overarching goal of this proposal is to define how perioperative positive end-expiratory pressure alters biventricular mechanics and right ventricular-pulmonary arterial coupling, to inform physiologically guided, RV-protective ventilatory strategies during 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)