Obese Lung-Transplant Recipients At Higher Risk Of Death

April 1, 2002

GAINESVILLE, Fla. — Obese people are three times more likely to die after a lung transplant than individuals at healthier weights, providing first-time evidence that extremely heavy people should lose weight before having lung transplant surgery, University of Florida researchers have found.

“Our results are significant in that they provide some scientific evidence for what has likely been the clinical experience of transplant programs, that obese patients probably have higher morbidity and shorter survival after lung transplantation,” said James Rodrigue, Ph.D., an associate professor in the UF College of Health Professions’ clinical and health psychology department, who is one of the study’s principal investigators.

“Our findings also highlight the need for obese patients to participate actively in a weight-reduction program before transplantation,” he said.

The findings were published in the February issue of Chest, the journal of the American College of Chest Physicians.

“Recently developed guidelines have suggested that obese people should not be eligible to receive transplants until they are no more than 30 percent above their ideal weights, but the UF study is the first to provide evidence of the harmful effects that abnormal weight, particularly obesity, play in patients’ outcomes after lung transplantation,” said Maher Baz, M.D., an assistant professor in the College of Medicine’s department of medicine, division of pulmonary and critical care, and the study’s other principal investigator.

More than half of adult Americans are considered overweight or obese by World Health Organization guidelines. In addition to an association with heart disease, diabetes and hypertension, obesity adversely affects lung function. It increases an individual’s respiratory muscle demand, requiring more oxygen consumption than normal. The added strain on the lungs and muscles involved in breathing can damage an obese person’s respiratory system.

More than 3,800 Americans who suffer from such diseases as chronic obstructive pulmonary disease, emphysema, chronic bronchitis, asthma and cystic fibrosis are waiting for lung transplants, according to the United Network for Organ Sharing. In 2000, less than 1,000 received transplants because of the scarcity of donated organs.

In the UF study, researchers followed through the fall of 2000 the progress of 85 patients who had undergone lung transplants at Shands at UF medical center between March 1994 and October 1998. Using WHO’s body mass index measure – dividing weight in kilograms by height in meters squared – the transplant recipients were grouped into four categories: underweight (BMI score below 18.5), normal weight (BMI 18.5 to 24.9), overweight (BMI 25 to 29.9) and obese (BMI 30 and above). An individual who is 5 feet 8 inches tall and weighs 197 pounds, for example, has a BMI of 30.

Twelve percent of the study’s patients were obese before their lung transplantation.

UF researchers discovered that the underweight patients had a superior survival rate – above 80 percent – for the first four years after transplant, but survival rates fell to 50 percent after that time. Researchers were surprised to learn that patients who were overweight had similar survival rates as their normal-weight counterparts, who had rates as high as 90 percent in the first two years after transplant and 70 percent thereafter. Obese patients, however, experienced the lowest survival rates. After transplantation, their survival rates steadily fell to 30 percent at two years and beyond.

UNOS data show the national average for lung-transplant survival rates is 75.8 percent at one year and 55.6 percent at three years.

UF researchers theorize that increased respiratory demands and altered respiratory muscle mechanics caused by obesity led to the high mortality rates in obese lung-transplant recipients.

“Not only is it more difficult for obese patients to recover after a major chest operation, but their impaired respiratory muscles make it very difficult for them to recover after setbacks such as pneumonia or rejection, complications that are probably better tolerated by patients that are not obese,” Baz said.

Rodrigue suggested that additional research studies on obesity and lung-transplant recipients should include a larger group of patients, an examination of the role weight gain plays on survival after a lung transplant, the mechanisms responsible for the shortened survival, and the types of weight-management strategies that are most effective in extending survival after lung transplants.

“Our findings should force a discussion among transplant professionals about what to do with obese patients who may need lung transplantation,” Rodrigue said. “Perhaps the bottom line is that lung-transplant programs should offer behavioral health services to their patients to help them lose weight and make other necessary lifestyle adjustments.”