Characterization of Donor to Recipient Size Matching in Lung Transplantation

Rationale: Donor to recipient lung size matching is an important aspect of lung transplantation (LTx). Height is an important predictor of lung size. However gender affects lung size independent of height. The predicted total lung capacity (pTLC), as an estimate of lung size, can be calculated from regression equations based on gender and height. Objective: To characterize the donor-recipient lung size matching based on the pTLC ratio (= pTLC donor/pTLC recipient), height and gender. Methods: All adult patients in the United Network for Organ Sharing (UNOS) transplant registry who underwent first-time LTx between October 1989 and April 2010 were studied, and the pTLC ratio was calculated. Subjects were then grouped into pTLC ratio strata (stratum 1: pTLC ratio<0.8 “very undersized”; stratum 2: pTLC ratio 0.8-1.0 “undersized”; stratum 3: pTLC ratio 1.0-1.2 “oversized” and stratum 4: pTLC ratio>1.2 “very oversized”). Results: The pTLC ratio was available for 17,779 of the 19,812 study patients (89.7%). The mean pTLC ratio was 1.07 � 0.21 (range 0.4 – 2.0). The mean pTLC ratio progressively decreased by transplant era from 1.14 in 1989 to 1.04 in 2010 (p <0.0001). Subjects in “size matched” strata 2 and 3 were 83% and 93% gender matched. In the very undersized stratum 1 87% of patients had a female donor to male recipient gender-mismatch, whereas in the very oversized stratum 4 80% of patients had a male donor to female recipient gender-mismatch. In the group of subjects with restrictive lung disease the percentage the very undersized stratum 1 increased from 5.9% in the 1989- 1994 eras to 16.4% in the 2006-2010 eras. Conclusion: Donor-recipient lung size matching is best estimated by donor to recipient pTLC ratio, as the important effect of gender on lung size is accounted for in this metric. The evolution towards lower pTLC ratio's (more under sizing) over time, especially for restrictive lung diseases, is contrary to the growing evidence showing the outcome benefits of oversized allograft.