Size-matching in lung transplantation using the adjusted total lung capacity ratio

Evidence guiding optimal size-matching in lung transplantation is limited, and no consensus exists. Most current approaches fail to account for the recipient's underlying pathology. A recently proposed "adjusted" total lung capacity (TLC) ratio, incorporating actual (aTLC) and predicted TLC (pTLC), may offer a physiologically relevant size-matching strategy. However, its clinical performance has not been reported.

We retrospectively reviewed 376 double lung transplants at our center between January 2017 and March 2023, excluding lobar transplants. We calculated the adjusted TLC ratio as the donor pTLC divided by the mean of the recipient pTLC and aTLC. Patients were categorized into 3 groups as follows: all recipients (Cohort A, n = 376), restrictive lung disease (Cohort B, n = 204), and restrictive disease without volume-reduction procedures (Cohort C, n = 150). The primary outcome was peak posttransplant forced expiratory volume in 1 s (FEV1). Secondary outcomes included baseline lung allograft dysfunction (BLAD), chronic lung allograft dysfunction (CLAD), survival, and time to normalization of lung function.

Based on posttransplant peak FEV1, we identified an adjusted TLC ratio of 0.9 to 1.0 as the optimal range for lung-size matching. Optimally sized (0.9-1.0) and undersized (0.79-0.89) grafts showed the highest FEV1 posttransplant. Oversized grafts (>1.0) were associated with lower FEV1 across all cohorts and higher BLAD incidence in Cohort A. The adjusted TLC ratio did not influence survival.

Size-matching using an adjusted TLC ratio of 0.79 to 1.0 correlates with improved long-term outcomes in lung transplantation, whereas oversizing may impair lung function. The effect on survival remains inconclusive due to study limitations.