High Pleural Pressure Prevents Alveolar Overdistension and Hemodynamic Collapse in Acute Respiratory Distress Syndrome with Class III Obesity A Clinical Trial

Rationale: Obesity is characterized by elevated pleural pressure (Ppl) and worsening atelectasis during mechanical ventilation in patients with acute respiratory distress syndrome (ARDS). Objectives: To determine the effects of a lung recruitment maneuver (LRM) in the presence of elevated Ppl on hemodynamics, left and right ventricular pressure, and pulmonary vascular resistance. We hypothesized that elevated Ppl protects the cardiovascular system against high airway pressure and prevents lung overdistension. Methods: First, an interventional crossover trial in adult subjects with ARDS and a body mass index >= 35 kg/m(2) (n = 21) was performed to explore the hemodynamic consequences of the LRM. Second, cardiovascular function was studied during low and high positive end-expiratory pressure (PEEP) in a model of swine with ARDS and high Ppl (n = 9) versus healthy swine with normal Ppl (n = 6). Measurements and Main Results: Subjects with ARDS and obesity (body mass index = 57612 kg/m(2)) after LRM required an increase in PEEP of 8 (95% confidence interval [95% CI], 7-10) cm H2O above traditional ARDS Network settings to improve lung function, oxygenation and V/Q matching, without impairment of hemodynamics or right heart function. ARDS swine with high Ppl demonstrated unchanged transmural left ventricular pressure and systemic blood pressure after the LRM protocol. Pulmonary arterial hypertension decreased (8 [95% CI, 13-4] mm Hg), as did vascular resistance (1.5 [95% CI, 2.2-0.9] Wood units) and transmural right ventricular pressure (10 [95% CI, 15-6] mm Hg) during exhalation. LRM and PEEP decreased pulmonary vascular resistance and normalized the V/Q ratio. Conclusions: High airway pressure is required to recruit lung atelectasis in patients with ARDS and class III obesity but causes minimal overdistension. In addition, patients with ARDS and class III obesity hemodynamically tolerate LRM with high airway pressure.