Baseline Gas Transfer (KCO) and Accessible Alveolar Volume (VA) after Lung Transplant: Determinants and Relative Contributions on Graft Survival

Purpose Low baseline diffusing capacity (DLCO), at 1-year after lung transplant, is associated with an increased risk of graft loss. DLCO is the product of 2 measurements; the gas transfer factor (KCO) and the accessible alveolar volume (VA). Our aim was to understand the relative contributions of baseline KCO and VA on survival after lung transplant. Methods A retrospective cohort analysis was conducted of all bilateral lung transplant recipients between 1998 and 2018, with DLCO measured at 1 year after transplant. Low baseline VA was defined as 80%-pred. Patients were divided into 4 groups: Normal VA-Normal KCO, Normal VA-Low KCO, Low VA-Normal KCO, Low VA-Low KCO. Multivariate logistic regression and Cox proportional hazard models were used for statistical analysis. Results 708 patients underwent double lung transplant during the study period. 258 patients had DLCO measured at 1-year post transplant. The mean recipient age was 44.0 (SD 15.5) with 50% males. The median time to measurement of DLCO was 378 days. The median (IQR) VA %-pred was 82 (21), %-Pred KCO 74 (19) and %-Pred FEV1 84 (29). Donor age was significantly associated with low KCO OR 1.06 (95%CI 1.03-1.08), p Conclusion Donor age, ILD and transplant era were associated with baseline KCO and VA. Low baseline VA was a greater risk for future graft loss than low KCO. There may be benefit in the incorporation of baseline VA and KCO at 1-year post transplant to identify patients with an increased risk of graft loss.