Pulmonary Dead Space Fraction: A Predictive Factor for Transplant Suitability in Clinical Ex Vivo Lung Perfusion

Abstract

<h3>Purpose</h3> Dead space fraction (DSF) correlates with disease severity in cases of pulmonary embolism (PE) and lung injury, and with mortality in acute respiratory distress syndrome. We sought to determine the relationship between DSF and donor lung transplant suitability during clinical ex vivo lung perfusion (EVLP). <h3>Methods</h3> DSF was calculated in 80 consecutive double lung cases undergoing acellular EVLP from 6/2019 to 8/2021 in our department. 53 cases were judged suitable for transplant. End-tidal CO₂ and CO₂ levels in perfusate were measured, and DSF stratified into quartiles (Q1, lowest; Q4, highest). DSF was calculated using the following formula: (PCO₂ in left atrium - End tidal CO₂) / PCO₂ in left atrium. <h3>Results</h3> Tobacco use history correlated with significantly higher DSF (vs. no tobacco use history, (<i>p</i> < 0.05). Presence of PE also correlated with higher DSF (<i>p</i> < 0.05). Lungs in the highest DSF quartile (Q4) displayed significantly higher peak airway pressure, lower PaO₂/FiO₂, and lower dynamic compliance during EVLP (<i>p</i> < 0.01, each; <b>Figure A-D</b>). The Q4 DSF group also had higher lung weight following EVLP (<i>p</i> < 0.05). Transplant suitability decreased with higher DSF; 85% (17/20 cases) of Q1, 85% (17/20 cases) of Q2, 60% (12/20 cases) of Q3, and 35% (7/20 cases) of Q4 (<i>p</i> < 0.01, <b>Figure E</b>) lungs were suitable for transplant. Of the 53 EVLP cases transplanted, 30-day recipient survival was 98% and the incidence of Grades 0, 1, 2, and 3 primary graft dysfunction at 72 hours was 19%, 57%, 13%, and 6%, respectively with 3 ungradable cases. <h3>Conclusion</h3> In human lungs undergoing acellular EVLP, higher DSF correlates with decreased transplant suitability. Further studies are needed to establish mechanisms by which high DSF contributes to lower transplant suitability.