Effects on Pulmonary Vascular Mechanics of Two Different Lung-Protective Ventilation Strategies in an Experimental Model of Acute Respiratory Distress Syndrome

Abstract

Objectives: To compare the effects of two lung-protective ventilation strategies on pulmonary vascular mechanics in early acute respiratory distress syndrome. Design: Experimental study. Setting: University animal research laboratory. Subjects: Twelve pigs (30.8 +/- 2.5 kg). Interventions: Acute respiratory distress syndrome was induced by repeated lung lavages and injurious mechanical ventilation. Thereafter, animals were randomized to 4 hours ventilation according to the Acute Respiratory Distress Syndrome Network protocol or to an open lung approach strategy. Pressure and flow sensors placed at the pulmonary artery trunk allowed continuous assessment of pulmonary artery resistance, effective elastance, compliance, and reflected pressure waves. Respiratory mechanics and gas exchange data were collected. Measurements and Main Results: Acute respiratory distress syndrome led to pulmonary vascular mechanics deterioration. Four hours after randomization, pulmonary vascular mechanics was similar in Acute Respiratory Distress Syndrome Network and open lung approach: resistance (578 +/- 252 vs 626 +/- 153 dyn. s/cm(5); p = 0.714), effective elastance, (0.63 +/- 0.22 vs 0.58 +/- 0.17 mm Hg/mL; p = 0.710), compliance (1.19 +/- 0.8 vs 1.50 +/- 0.27 mL/mm Hg; p = 0.437), and reflection index (0.36 +/- 0.04 vs 0.34 +/- 0.09; p = 0.680). Open lung approach as compared to Acute Respiratory Distress Syndrome Network was associated with improved dynamic respiratory compliance (17.3 +/- 2.6 vs 10.5 +/- 1.3 mL/cm H2O; p < 0.001), driving pressure (9.6 +/- 1.3 vs 19.3 +/- 2.7 cm H2O; p < 0.001), and venous admixture (0.05 +/- 0.01 vs 0.22 +/- 0.03, p < 0.001) and lower mean pulmonary artery pressure (26 +/- 3 vs 34 +/- 7 mm Hg; p = 0.045) despite of using a higher positive endexpiratory pressure (17.4 +/- 0.7 vs 9.5 +/- 2.4 cm H2O; p < 0.001). Cardiac index, however, was lower in open lung approach (1.42 +/- 0.16 vs 2.27 +/- 0.48 L/min; p = 0.005). Conclusions: In this experimental model, Acute Respiratory Distress Syndrome Network and open lung approach affected pulmonary vascular mechanics similarly. The use of higher positive end-expiratory pressures in the open lung approach strategy did not worsen pulmonary vascular mechanics, improved lung mechanics, and gas exchange but at the expense of a lower cardiac index.