Higher Donor BMI Tied to Improved Lung Transplant Survival

Lung transplant patients who received a lung from obese donors had a 15-20% reduction in mortality at 1 year in one of the first studies to examine the impact of donor body mass index (BMI) and post-transplant survival.

Findings from the retrospective trial, which included data on patients and donors registered with the United Network for Organ Sharing Standard Transplant and Analysis database, suggest that donor obesity may confer a protective benefit for transplanted lungs.

The findings were presented this week in a poster session at the virtual CHEST conference, the annual meeting of the American College of Chest Physicians.

The BMI of lung transplant recipients has been shown to be an independent predictor of mortality, with studies showing an increased risk of death following transplant in patients who are either underweight or overweight, said Sung Choi, MD, of Rutgers New Jersey Medical School in Newark, who presented the findings.

For example, in a 2017 study involving over 17,000 lung transplants performed in the U.S. from 2005 to 2016, underweight and overweight lung recipients (i.e., BMI ≤20 and ≥28 at the time of listing) were found to be at increased risk for both short- and long-term mortality.

Recipient weight-loss prior to lung transplantation was also associated with a reduction in mortality and days on mechanical ventilation in a 2015 study, with greater reductions in BMI associated with greater survival benefit.

And, in a 2014 consensus statement, the International Society for Heart and Lung Transplantation recommended that a BMI of 30 or greater be considered a relative contraindication to lung transplantation.

Regarding donor BMI, however, Choi told MedPage Today that there hasn’t been prior research examining the impact on lung recipient outcomes and that the findings from his team’s study were a surprise: “We really weren’t expecting this result,” he said.

“We thought greater donor BMI might be associated with an increase in recipient mortality or maybe a null finding. What we found was striking to us. There appeared to be a dose-dependent relationship, with higher donor BMI associated with lower recipient mortality at 90 days and 1 year after the transplant,” Choi said.

Close to 16,000 adult patients who received single- or double-lung transplants from 2005 to 2018 were included in the analysis. Median age of the lung recipients was 59, and roughly 60% were male. Donors were categorized as underweight (BMI <18.5), normal weight (18.5 to <25), overweight (25 to <30), class I obesity (30 to <35), class II obesity (35 to <40), and class III obesity (≥40.0).

Average donor BMI was 25.9, and 45% were classified as normal weight.

A survival benefit at 1 year was observed among patients who received a lung transplant from donors in obesity class 1 (HR 0.867, 95% CI 0.772-0.975, P<0.01) and obesity classes II/III (HR 0.804, 95% CI 0.688-0.941, P<0.01) compared with lungs from normal-weight donors, the researchers reported.

In adjusted analyses, the team reported lower odds of survival with increased donor age, male sex, and presence of diabetes.

Choi told MedPage Today that the findings led the researchers back to the published literature in an effort to understand the possible mechanism involved. They found two studies — one in rats and the other in deceased patients — both of which suggested a role for obesity-related chronic adaption to hypoxic conditions.

In the rat study, lungs of young obese rats showed alveolar enlargement with diminished respiratory surface area when compared with those from normal-weight controls.

In the study of autopsy findings from 76 obese people matched to non-obese controls, alveolar capillary hemangiomatosis was exclusively seen in the obese subjects, with 72% exhibiting venous hypertension and capillary hemangiomatosis.

Choi said that although it is possible that the chronic hypoxic state associated with obesity may lead to advantages in lungs harvested from obese people, additional studies are still needed to confirm the association and further explore possible mechanisms.