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 [8-10] cmH 2 O), ARDSnet-high (12 [12-12] cmH 2 O), OLC (21 [20-22] cmH 2 O). The fraction of arterial partial pressure of oxygen and inspired oxygen fraction ( p = 0.0016) was lowest in ARDSnet-low (78 (73-111) mm Hg) compared with ARDSnet-high (375 (365-423) mm Hg) and OLC (499 (430-523) mm Hg). The end-expiratory lung volume (EELV) differed significantly ( p < 0.0001), with highest values in OLC (64% [60-70%]) and lowest in ARDSnet-low (34% [24-37%]). Costa's surrogate for mechanical power differed significantly ( p < 0.0001), with lowest values for ARDSnet-high (73 [58-76]) compared with OLC (105 [108-116]). 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.

Detection of posttraumatic pneumothorax using electrical impedance tomography-An observer-blinded study in pigs with blunt chest trauma.

INTRODUCTION: Posttraumatic pneumothorax (PTX) is often overseen in anteroposterior chest X-ray. Chest sonography and Electrical Impedance Tomography (EIT) can both be used at the bedside and may provide complementary information. We evaluated the performance of EIT for diagnosing posttraumatic PTX in a pig model. METHODS: This study used images from an existing database of images acquired from 17 mechanically ventilated pigs, which had sustained standardized blunt chest trauma and had undergone repeated thoracic CT and EIT. 100 corresponding EIT/CT datasets were randomly chosen from the database and anonymized. Two independent and blinded observers analyzed the EIT data for presence and location of PTX. Analysis of the corresponding CTs by a radiologist served as reference. RESULTS: 87/100 cases had at least one PTX detected by CT. Fourty-two cases showed a PTX > 20% of the sternovertebral diameter (PTXtrans20), whereas 52/100 PTX showed a PTX>3 cm in the craniocaudal diameter (PTXcc3), with 20 cases showing both a PTXtranscc and a PTXcc3. We found a very low agreement between both EIT observers considering the classification overall PTX/noPTX (κ = 0.09, p = 0.183). For PTXtrans20, sensitivity was 59% for observer 1 and 17% for observer 2, with a specificity of 48% and 50%, respectively. For PTXcc3, observer 1 showed a sensitivity of 60% with a specificity of 51% while the sensitivity of observer 2 was 17%, with a specificity of 89%. By programming a semi-automatized detection algorithm, we significantly improved the detection rate of PTXcc3, with a sensitivity of 73% and a specificity of 70%. However, detection of PTXtranscc was not improved. CONCLUSION: In our analysis, visual interpretation of EIT without specific image processing or comparison with baseline data did not allow clinically useful diagnosis of posttraumatic PTX. Multimodal imaging approaches, technical improvements and image postprocessing algorithms might improve the performance of EIT for diagnosing PTX in the future.