When it comes to lung transplants, bigger may be better. That's the main finding from a University of Iowa study, which found that oversized lungs lead to improved survival following lung transplants, particularly among patients receiving double-lung transplants.
Currently, in the United States height is used as a surrogate for lung size for transplant candidates. But Michael Eberlein, clinical assistant professor in internal medicine at the UI, and colleagues came up with a new formula, called "predicted total lung capacity ratio," to find out which size lungs matched best with patients who are candidates for transplants.
"An unresolved question in the field of lung transplantation is how the size of the donor lungs relative to the recipient affects transplant success," he explains. "It is commonly believed that transplanting oversized lungs is problematic, but no data were available to substantiate that idea."
The pTLC ratio is calculated using height and gender. Taller people have bigger lungs and a man's lungs are larger than a woman's of the same height. The pTLC-ratio is determined by dividing the donor's pTLC by the patient's pTLC. A ratio of 1.0 is a perfect size match, whereas for example a ratio of 1.3 indicates that the donor lung is significantly larger than the patient's lung.
Eberlein and colleagues used data from the United Network for Organ Sharing (UNOS) lung transplant registry for all adult patients (aged 18 years and older) who underwent first-time lung transplantation between May 2005 and April 2010. Of the 6,997 patients included in the study, 4,520 underwent bilateral lung transplant and 2,477 underwent single lung transplant.
For patients undergoing a double-lung transplant, the team found that each 0.1 increase in the predicted total lung capacity (pTLC) ratio was associated with a 7 percent decrease in risk of death a year after the procedure. This decrease was still independently associated with improved survival following additional adjustment to account for any bias to oversizing. For those receiving one lung, each 0.1 increase in pTLC-ratio was associated with a 6 percent decrease in the risk of death a year later; however, this association was not present following the same additional adjustment to account for any bias to oversizing.
"This study shows that lung size matters in lung-transplant procedures," says Eberlein, lead author of the study published Aug. 1 in the journal The Annals of Thoracic Surgery. "We found that oversized allografts, up to a point, were associated with improved survival after lung transplantation. We would hope that recipients, within surgically feasible limits, could be listed for higher donor height ranges and ultimately have a better chance of receiving an acceptable donor lung."
In an editorial in the same issue of The Annals, Seth Force, from Emory University School of Medicine in Atlanta, praised the work. "The real strength of this study may be in showing that utilizing pTLC allows for a more standardized way of matching donor lungs compared to the height method," Force says. "The data in this manuscript make a compelling argument for the lung transplant community, as well as UNOS, to consider changing to a pTLC method for lung sizing for listed patients."
Contributing authors include Kalpai Parekh and Lawrence Hunsicker from the UI; Servet Bolukbas from the Dr. Horst Schmidt Klinik in Wiesbaden, Germany; George Arnaoutakis, Jonathan Orens, Roy Brower, Ashish Shah and Christian Merlo from the Johns Hopkins University School of Medicine; and Robert Reed from the University of Maryland School of Medicine.
There was no outside funding for the study.