Evidence of Air Trapping During Ex Vivo Lung Perfusion: A Swine Experimental Lung Imaging and Mechanics Study

Ex vivo lung perfusion (EVLP) allows the ventilation and perfusion of lungs to evaluate their viability for transplantation. The aim of this study is to compare the mechanical, morphologic and functional properties of lungs during EVLP with values obtained in vivo to guide a safe mechanical ventilation strategy. Lungs from 5 healthy pigs were studied in vivo and during 4 hours of EVLP. Lung compliance, airway resistance, gas exchange, and hemodynamic parameters were collected at positive end-expiratory pressure (PEEP) of 5 cm H₂O. Computed tomography was performed at PEEP 0, PEEP 5, and total lung capacity (TLC). Lung pressure-volume (PV) curves were performed from PEEP 0 to TLC. Lung compliance decreased during EVLP (53 ± 5 mL/cm H₂O vs 29 ± 7 mL/cm H₂O, P < .05), and the PV curve showed a lower inflection point. Gas content (528 ± 118 mL vs 892 ± 402 mL at PEEP 0) and airway resistance (25 ± 5 vs 44 ± 9 cmH₂O/L∗s^-1, P < .05) were higher during EVLP. Alveolar dead space (5% ± 2% vs 17% ± 6%, P < .05) and intrapulmonary shunt (9% ± 2% vs 28% ± 13%, P < .05) increased ex vivo compared to in vivo, while the partial pressure of oxygen to inspired oxygen fraction ratio (PO₂/FiO₂) did not differ (468 ± 52 mm Hg vs 536 ± 14 mm Hg). In conclusion, during EVLP lungs show signs of air trapping and bronchoconstriction, resulting in low compliance and increased alveolar dead space. Intrapulmonary shunt is high despite oxygenation levels acceptable for transplantation.