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For lung transplants, bigger is better

JOHNS HOPKINS (US) — Oversized donor lungs may be a better, safer fit for lung transplant recipients than organs matched to the size of the patient, research suggests.

As illustrated by a recent Pennsylvania controversy involving a 10-year-old girl in need of new lungs, transplant teams have long tried to match donor lungs to the size of the recipient as closely as possible. The concern has been that lungs of the wrong size could lead to poor lung function and poor outcomes.

But the new study found that transplanting oversized lungs is associated with a 30 percent increased chance of survival one year after the operation.

“Despite what we thought, bigger lungs turn out to be better,” says Christian A. Merlo, a lung transplant expert at the Johns Hopkins University School of Medicine.

“The survival rates for lung transplant, unfortunately, are not as good as with other solid organ transplants like liver, kidney and heart,” he says. “But our study tells us that if we were to routinely transplant larger lungs into patients, we could potentially make a real impact on survival. And that’s the goal of research.”

The issue of lung size leaped into the spotlight recently with the case of the 10-year-old Pennsylvania patient. Regulations have made children younger than 12 ineligible to receive adult lungs, primarily because of the potential size mismatch.

Her situation sparked a national debate on organ allocation procedures, and her family successfully petitioned the courts to enable her to receive lungs from an adult.

Lung size can be estimated from the height and sex of the patients and is termed the “predicted total lung capacity.” Taller people have bigger lungs and a man’s lungs are larger than a woman’s of the same height. Researchers define lung size mismatch as the ratio of the predicted lung capacity of the donor relative to the recipient.

For example, a ratio of 1.0 is a perfect size match, whereas a ratio of 1.3 indicates that the transplanted lung is significantly larger than the predicted total lung capacity for the recipient. Merlo’s research found that double lung transplant recipients who received lungs with an average ratio of 1.3 were 30 percent less likely to die in the first year.

Powerful predictor of survival

For the study, published in the Annals of Thoracic Surgery, researchers analyzed data from 4,520 double lung transplants and 2,477 US single lung transplants performed between 2005 and 2010.

The findings were clearer about the benefits of larger lungs in double lung transplants than in single ones, though oversized lungs did convey some survival benefit in those cases as well.

“Size is a more powerful predictor of survival than we ever thought,” says Ashish S. Shah, associate professor of surgery and surgical director of lung transplantation at Johns Hopkins Hospital and another study author. “Fears of oversized lungs appear to be unfounded. We hope this research dispels some myths.”

In lung transplant, the sickest patients move to the top of the list. Once an adult patient is atop the list, height, sex and blood type are used to determine whether those lungs are suitable for that patient.

Merlo and Shah say it might be better to build in a calculation for predicted lung capacity. That way, oversized lungs could be offered to patients instead of smaller lungs that may not work as well.

Lungs can be too large, they caution. Beyond a certain size, surgeons could have trouble closing the chest cavity, the lungs could be too compressed and collapse or could weigh too heavily on the heart, causing low blood pressure and other problems.

Currently, children younger than 12 cannot receive adult lungs and adults cannot receive lungs from pediatric donors. The new findings suggest that there may be some benefit to removing age from the equation altogether when allocating lungs, putting children and adult donors and recipients into the same pool.

Then, doctors could make decisions based on each individual case and the size of the donor organs that become available.

“This study tells us that rather than looking at things like age or height, you have to look at each patient very carefully and determine what their lung capacity is,” Shah says.

“There may be children who could take adult lungs that would be oversized for them with a good result. And there may be small adults who would do well with pediatric lungs.”

Still, while larger lungs may be ideal, transplant candidates who don’t get new organs are more likely to die, so smaller lungs are often better than none at all.

There are currently more than 1,600 people listed for lung transplants in the United States and many die before getting new lungs. One-year survival after lung transplantation is 80 percent.

The research was supported in part by the Health Resources and Services Administration

Source: Johns Hopkins University

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