LAUSR

Abstract Background Evaluation of donor lung function relies on the arterial oxygen partial pressure to inspired oxygen fraction ratio (PaO2/FiO2) measurement. Hemodynamic, metabolic derangements, and therapeutic intervention occurring during brain dead observation may influence the evaluation of gas exchange. Methods We performed a mathematical analysis to explore the influence of the extrapulmonary determinants on the interpretation of PaO2/FiO2 in the brain‐dead donor and during Ex‐Vivo Lung Perfusion (EVLP). Results High FiO2 and increased mixed venous oxygen saturation, caused by increased delivery and reduced consumption of oxygen, raise the PaO2/FiO2 despite substantial intrapulmonary shunt. Anemia does not modify the PaO2/FiO2—intrapulmonary shunt relationship. During EVLP, the reduced artero‐venous difference in oxygen content increases the PaO2/FiO2 without this corresponding to an optimal graft function, while the reduced perfusate oxygen‐carrying capacity linearizes the PaO2/FiO2—intrapulmonary shunt relationship. Conclusions Adopting PaO2/FiO2 to evaluate graft suitability for transplantation should account for extrapulmonary factors affecting its interpretation.