Donor to recipient sizing in thoracic organ transplantation

Abstract

Donor-to-recipient organ size matching is a critical aspect of thoracic transplantation. In the United States potential recipients for lung transplant and heart transplant are listed with limitations on donor height and weight ranges, respectively. Height is used as a surrogate for lung size and weight is used as a surrogate for heart size. While these measures are important predictors of organ size, they are crude surrogates that fail to incorporate the influence of sex on organ size. Independent of other measures, a man's thoracic organs are approximately 20% larger than a woman's. Lung size can be better estimated using the predicted total lung capacity, which is derived from regression equations correcting for height, sex and age. Similarly, heart size can be better estimated using the predicted heart mass, which adjusts for sex, age, height, and weight. These refined organ sizing measures perform better than current sizing practice for the prediction of outcomes after transplantation, and largely explain the outcome differences observed after sex-mismatch transplantation. An undersized allograft is associated with worse outcomes. In this review we examine current data pertaining to size-matching in thoracic transplantation. We advocate for a change in the thoracic allocation mechanism from a height-or-weight-based strategy to a size-matching process that utilizes refined estimates of organ size. We believe that a size-matching approach based on refined estimates of organ size would optimize outcomes in thoracic transplantation without restricting or precluding patients from thoracic transplantation.

Keywords: Heart transplant; Lung transplant; Organ allocation; Organ size; Size mismatch.

Figure 1

Lung size mismatch (the donor to recipient predicted total lung capacity ratio) is associated with the probability of primary graft dysfunction grade 3. The relationship of pTLCratio (pTLCdonor/pTLCrecipeint) and predicted probability of any grade PGD grade 3 within 72 h is shown using a fractional polynomial fit with 95%CIs (gray area). Adapted with permission from Eberlein et al[14]. pTLC: Predicted total lung capacity; PGD: Primary graft dysfunction.

Figure 2

Conceptual graphic on the possible effect of lung size mismatch on mechanical ventilation tidal volumes expressed as mL/kg predicted body weights of the donor. Reproduced with permission from Dezube et al[15]. Recip recipient, Don donor. PBW: Predicted body weight; TV: Tidal volume.

Figure 3

Lung size mismatch (predicted total lung capacity ratio) is associated with the mechanical ventilation tidal volumes at reperfusion, when the tidal volumes is related to the size of the allograft. Fractional polynomial regression of the TV in mL/kg donor-predicted body weight (PBW) plotted against the pTLCratio (pTLCdonor/pTLCrecipeint). The solid vertical bars represent the mean values of the TV in mL/kg donor-PBW according to pTLCratio-quintiles. Adapted with permission from Eberlein et al[14]. TV: Tidal volumes; pTLC: Predicted total lung capacity.

Figure 4

Kaplan Meier estimates of proportion of patients with bronchiolitis obliterans syndrome stratified by recipients of undersized or oversized donor lungs. Oversized was defined as a donor to recipient predicted total lung capacity (pTLC) ratio > 1.0 and undersized as pTLCratio ≤ 1.0. Comparison between over- and undersized cohorts was via log-rank test. Adapted with permission from Eberlein et al[5]. BOS: Bronchiolitis obliterans syndrome.

Figure 5

Oversized allograft (A) and chest wall strapping (B) analogy. A: Schematic flow volume loops according to donor predicted values (black line) and measured mean values of recipients of oversized allografts (red line) during the early post-transplant period (1-6 mo). Flows are plotted against absolute lung volume; B: Control (blue) and chest wall strapped (orange) flow volume loops are shown. Adapted with permission from Eberlein et al[5,28].

Figure 6

Impact of predicted total lung capacity ratio on the risk of death after lung transplant. Adapted with permission from Eberlein et al[6]. pTLC: Predicted total lung capacity.

Figure 7

Mean predicted total lung capacity ratio according to transplant year stratified by lung transplant indication. Adapted with permission from Taher et al[34]. pTLC: Predicted total lung capacity; CF: Cystic fibrosis; COPD: Chronic obstructive pulmonary disease; IPF: Idiopathic pulmonary fibrosis; IPAH: Idiopathic pulmonary arterial hypertension.

Figure 8

Unadjusted Kaplan-Meier graphs of survival, by septiles of matching by body weight (A) vs predicted total heart mass (B). Adapted with permission from Reed et al[2].

Figure 9

Relationship between predicted total lung capacity ratio and height ratio. The separation between clusters I (male donor-female recipient), II (sex matched) and III (female to male) is due to effects of sex on lung size. Adapted with permission from Eberlein et al[7]. pTLC: Predicted total lung capacity.