Hemodynamic effects of different lung-protective ventilation strategies in closed-chest pigs with normal lungs

OBJECTIVE: The benefits of lung-protective ventilation strategies used for acute respiratory distress syndrome in subjects with normal lungs are uncertain. The purpose of this study was to investigate the hemodynamic effects of conventional lung-protective ventilation (CLPV) and high-frequency oscillatory ventilation (HFOV) in a normal lung animal model. DESIGN: Prospective laboratory investigation. SETTING: Animal laboratory in a university medical center. SUBJECTS: Seven landrace pigs (mean weight 41 kg). INTERVENTIONS: Pigs were ventilated at random conventionally with positive end-expiratory pressure 2-3 cm H2O and tidal volume 10-12 mL/kg (control), with CLPV (positive end-expiratory pressure 10 cm H2O, tidal volume 6 mL/kg), or with HFOV. Hemodynamics were analyzed after insertion of biventricular conductance catheters and a pulmonary artery catheter. MEASUREMENTS AND MAIN RESULTS: The protective strategies led to higher mean airway pressures and severe hypercapnia with acidosis, which was only significant with CLPV. Compared with control, oxygenation was worse with CLPV and HFOV. With HFOV and CLPV, mean arterial pressure, cardiac output, and stroke volume decreased significantly; pulmonary arterial elastance increased. The slope of the end-diastolic pressure volume relationship for the left and right ventricle remained unchanged (preserved ventricular function), whereas the intercept increased with both protective strategies (augmented intrathoracic pressure); left and right end-diastolic volumes decreased significantly. CONCLUSIONS: In the absence of a fluid resuscitation strategy, CLPV and HFOV caused decreased mean arterial pressure, cardiac output, and stroke volume and worsened oxygenation in this normal lung animal model. This resulted primarily from a biventricular decrease in preload.