The influence of positive end-expiratory pressure on stroke volume variation and central blood volume during open and closed chest conditions.

OBJECTIVE: Intermittent positive pressure ventilation and positive end-expiratory pressure (PEEP) affect cardiac preload. Their effect is dependent on chest wall compliance. This study compares the effects of intermittent positive pressure ventilation and PEEP on stroke volume variation and central blood volume during open and closed chest conditions. MATERIALS AND METHODS: Fourteen anesthetized and mechanically ventilated pigs (25-40 kg) were studied. Central blood volume was assessed using global end-diastolic volume and right ventricular end-diastolic volume measured by thermodilution. Further, left and right ventricular stroke volume variations were determined with ultrasonic flow probes placed around the pulmonary artery and ascending aorta, respectively. Measurements were performed during mechanical ventilation without and with PEEP (15 cmH(2)O) in open and closed chest conditions. RESULTS: With the chest closed mean arterial pressure, cardiac output, stroke volume, global end-diastolic volume, and right ventricular end-diastolic volume were significantly lower when compared to open chest conditions. Concomitantly, right ventricular, but not left ventricular stroke volume variation increased significantly. Applying PEEP led to a significant reduction of cardiac output, stroke volume and right ventricular end-diastolic volume, with a concomitant increase in left and right ventricular stroke volume variation both during open and closed chest conditions (all P-values<0.05). CONCLUSIONS: We conclude that PEEP increases right and left ventricular stroke volume variation both during open and closed chest conditions. The concomitant reduction of right ventricular end-diastolic volume further indicates that PEEP has a preload reductive effect during open chest conditions, too.