Dynamics of acute respiratory distress syndrome development due to smoke inhalation injury: Implications for prolonged field care

BACKGROUND: Smoke inhalation injury (SII) causes 30% to 40% mortality and will increase as a cause of death during prolonged field care. We used a combat relevant model of acute respiratory distress syndrome due to SII to study temporal changes in ventilation-perfusion (V/Q) matching, computed tomography (CT) scan data, and histopathology and hypothesized that SII leads to increase in shunt (Q_shunt), V/Q mismatch, lung consolidation, and diffuse alveolar damage. METHODS: Swine received severe SII and airway pressure release ventilation (APRV, n = 6), or conventional ARDSNet mechanical ventilation (MV) (CMV, n = 8). A control group without injury received volume controlled MV (CTRL, n = 6), The multiple inert gas elimination technique and CT were performed at baseline (BL), 0.5 hours, 1 hours, 2 hours, 24 hours, and 48 hours after injury. Diffuse alveolar damage scoring was performed post mortem. Significance at p less than 0.05: APRV versus CTRL^‡; CMV versus CTRL^†; APRV versus CMV*; ^& denotes changes versus BL. RESULTS: (1) SII caused increases in Q_shunt more so in APRV than CMV group. Q_shunt did not change in CTRL. (2) PaO₂-to-FIO₂ ratio (PFR) was lower in APRV versus CTRL at 2 hours (375 ± 62‡ vs. 549 ± 40) and 24 hours (126 ± 34‡*^& vs. 445 ± 5) and 48 hours (120 ± 41‡& vs. 430 ± 13). In CMV animals, PFR was lower versus CTRL and BL at 24 hours (238 ± 33^†&) and 48 hours (98 ± 27^†&). Q_shunt correlated with PFR (r = 0.75, p < 0.0001, APRV and (r = 0.65, p < 0.0001, CMV). CT showed decrease in normally aerated lung, while poorly and nonaerated lung increased. CONCLUSION: Smoke inhalation injury leads to early development of shunt, V/Q mismatch, lung consolidation, and diffuse alveolar damage. These data substantiate the need for new point of injury interventions in the prolonged field care setting.