High positive end-expiratory pressure ventilation mitigates the progression from unilateral pulmonary contusion to ARDS: An animal study

BACKGROUND Pulmonary contusion (PC) is common in severely traumatized patients and can lead to respiratory failure requiring mechanical ventilation (MV). Ventilator-induced lung injury (VILI) might aggravate lung damage. Despite underrepresentation of trauma patients in trials on lung-protective MV, results are extrapolated to these patients, potentially disregarding important pathophysiological differences. METHODS Three MV protocols with different positive end-expiratory pressure (PEEP) levels: ARDSnetwork lower PEEP (ARDSnet-low), ARDSnetwork higher PEEP (ARDSnet-high), and open lung concept (OLC) were applied in swine for 24 hours following PC. Gas exchange, lung mechanics, quantitative computed tomography, and diffuse alveolar damage (DAD) score were analyzed. Results are given as median (interquartile range) at 24 hours. Statistical testing was performed using general linear models (group effect) over all measurement points and pairwise Mann-Whitney U tests for DAD. RESULTS There were significant differences between groups: PEEP (p < 0.0001) ARDSnet-low (8 [810] cmH(2)O), ARDSnet-high (12 [1212] cmH(2)O), OLC (21 [2022] cmH2O). The fraction of arterial partial pressure of oxygen and inspired oxygen fraction (p = 0.0016) was lowest in ARDSnet-low (78 (73111) mm Hg) compared with ARDSnet-high (375 (365423) mm Hg) and OLC (499 (430523) mm Hg). The end-expiratory lung volume (EELV) differed significantly (p < 0.0001), with highest values in OLC (64% [6070%]) and lowest in ARDSnet-low (34% [2437%]). Costa's surrogate for mechanical power differed significantly (p < 0.0001), with lowest values for ARDSnet-high (73 [5876]) compared with OLC (105 [108116]). Diffuse alveolar damage was lower in ARDSnet-high compared with ARDSnet-low (0.0007). CONCLUSION Progression to ARDS, 24 hours after PC, was mitigated by OLC and ARDSnet-high. Both concepts restored EELV. ARDSnet-high had the lowest mechanical power surrogate and DAD. Our data suggest, that ARDSnet-high restored oxygenation and functional lung volume and reduced physiological and histological surrogates for VILI. ARDSnet-low generated unfavorable outcomes, such as loss of EELV, increased mechanical power and DAD after PC in swine. The high respiratory rate in the OLC may blunt favorable effects of lung recruitment.