Continuous Negative Abdominal Pressure Reduces Ventilator-Induced Lung Injury In A Porcine Model

Background: In supine patients with acute respiratory distress syndrome, the lung typically partitions into regions of dorsal atelectasis and ventral aeration ("baby lung"). Positive airway pressure is often used to recruit atelectasis, but often overinflates ventral (already aerated) regions. A novel approach to selective recruitment of dorsal atelectasis is by "continuous negative abdominal pressure.Methods: A randomized laboratory study was performed in anesthetized pigs. Lung injury was induced by surfactant lavage followed by 1h of injurious mechanical ventilation. Randomization (five pigs in each group) was to positive end-expiratory pressure (PEEP) alone or PEEP with continuous negative abdominal pressure (-5 cm H2O via a plexiglass chamber enclosing hindlimbs, pelvis, and abdomen), followed by 4h of injurious ventilation (high tidal volume, 20ml/kg; low expiratory transpulmonary pressure, -3cm H2O). The level of PEEP at the start was approximate to 7 (vs. approximate to 3) cm H2O in the PEEP (vs. PEEP plus continuous negative abdominal pressure) groups. Esophageal pressure, hemodynamics, and electrical impedance tomography were recorded, and injury determined by lung wet/dry weight ratio and interleukin-6 expression.Results: All animals survived, but cardiac output was decreased in the PEEP group. Addition of continuous negative abdominal pressure to PEEP resulted in greater oxygenation (Pao(2)/fractional inspired oxygen 316134 vs. 80 +/- 24 mmHg at 4h, P = 0.005), compliance (14.2 +/- 3.0 vs. 10.3 +/- 2.2ml/cm H2O, P = 0.049), and homogeneity of ventilation, with less pulmonary edema (approximate to 10% less) and interleukin-6 expression (approximate to 30% less).Conclusions: Continuous negative abdominal pressure added to PEEP reduces ventilator-induced lung injury in a pig model compared with PEEP alone, despite targeting identical expiratory transpulmonary pressure.