Cardiovascular Effects of Increasing Positive End-Expiratory Pressure in A Model of Left Ventricular Cardiogenic Shock in Female Pigs.

Abstract

Cardiogenic shock (CS) presents a medical challenge with limited treatment options. Positive end-expiratory pressure (PEEP) during mechanical ventilation has been linked with clinical benefits in patients with CS. We investigated if increasing PEEP levels could unload the left ventricle (LV) in CS in a large animal model of LV-CS. LV-CS was induced in 26 female pigs (60 kg) by microsphere injections into the left main coronary artery. In one study protocol PEEP was increased (5, 10, and 15 cmH2O) and then reverted (15, 10, 5 cmH2O) in 3-minute intervals. In another protocol PEEP increments with higher granularity were conducted through 3-minute intervals (5, 8, 10, 13, and 15 cmH2O). Hemodynamic measurements were performed at all PEEP levels during the healthy state and LV-CS with LV pressure-volume loops. The primary endpoint was pressure-volume area (PVA). Secondary endpoints included other mechano-energetic parameters and estimates of LV preload and afterload. Cardiac output (CO) decreased significantly in LV-CS from 4.5±1.0 L/min to 3.1±0.9 L/min (P<0.001). Increasing PEEP resulted in lower PVA, demonstrating a 36±3% decrease in the healthy state (P<0.001) and 18±3% in LV-CS (P<0.001) at PEEP 15 cmH2O. These effects were highly reversible when PEEP was returned to 5 cmH2O. While mean arterial pressure declined with higher PEEP, CO remained preserved during LV-CS (P=0.339). Increasing PEEP caused reductions in key measures of LV preload and afterload during LV-CS. Right ventricular stroke work index was decreased with increased PEEP. Despite a minor increase in heart rate (HR) at PEEP levels of 15 cmH2O (71 bpm vs. 75 bpm, p<0.05), total mechanical power expenditure (PVA normalized to HR) decreased at higher PEEP. Applying higher PEEP levels reduced PVA, preserving CO while decreasing MAP. PEEP could be a viable LV unloading strategy if titrated optimally during LV-CS.