Intra-abdominal hypertension (IAH) may co-occur with the
acute respiratory distress syndrome (ARDS), with significant impact on morbidity and mortality. Lung-protective controlled
mechanical ventilation with low tidal volume and
positive end-expiratory pressure (PEEP) has been recommended in ARDS. However,
mechanical ventilation with spontaneous breathing activity may be beneficial to lung function and reduce lung damage in mild ARDS. We hypothesized that preserving spontaneous breathing activity during pressure support ventilation (PSV) would improve respiratory function and minimize
ventilator-induced lung injury (VILI) compared to pressure-controlled ventilation (PCV) in mild extrapulmonary
acute lung injury (ALI) with IAH. Thirty Wistar rats (334±55g) received Escherichia coli
lipopolysaccharide intraperitoneally (1000μg) to induce mild extrapulmonary ALI. After 24h, animals were anesthetized and randomized to receive PCV or PSV. They were then further randomized into subgroups without or with IAH (15 mmHg) and ventilated with PCV or PSV (PEEP = 5cmH2O, driving pressure adjusted to achieve tidal volume = 6mL/kg) for 1h. Six of the 30 rats were used for molecular biology analysis and were not mechanically ventilated. The main outcome was the effect of PCV versus PSV on
mRNA expression of
interleukin (IL)-6 in lung tissue. Regardless of whether IAH was present, PSV resulted in lower mean airway pressure (with no differences in peak airway or peak and mean transpulmonary pressures) and less
mRNA expression of
biomarkers associated with
lung inflammation (IL-6) and fibrogenesis (
type III procollagen) than PCV. In the presence of IAH, PSV improved oxygenation; decreased alveolar collapse, interstitial
edema, and diffuse alveolar damage; and increased expression of
surfactant protein B as compared to PCV. In this experimental model of mild extrapulmonary ALI associated with IAH, PSV compared to PCV improved lung function and morphology and reduced type 2 epithelial cell damage.