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.