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IPAH Patients Overlooked on Lung Transplant List

Posted on: Friday, 28 August 2009, 07:20 CDT

Mortality remains high among patients awaiting lung transplant, despite changes to the allocation system that were designed to reduce mortality and increase the equitable distribution of donor organs, according to new research.

Previously, the only factor determining a patient’s priority was the amount of time he or she had been on the waiting list, but 2005 saw the implementation of a new allocation system based on a "lung allocation score" (LAS). LAS is determined by such factors as the patient's functional status, exercise capacity, lung function, hemodynamic data and the need for ventilator support.

Overall, mortality on the lung transplant waiting list has fallen as a result of the change, especially among patients with chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF) and cystic fibrosis (CF). Patients with idiopathic pulmonary arterial hypertension (IPAH), however, make up only a small minority of lung-transplant candidates, and therefore little is known about whether they have benefited from the changes to lung allocation protocols.

"Most people will agree that the LAS has improved organ allocation for most patients on the waiting list, but we wished to study how it has specifically affected patients with idiopathic pulmonary arterial hypertension (IPAH)—a condition for which the LAS may not adequately capture the severity of the patient's illness," Hubert Chen, M.D., M.P.H., assistant professor of medicine at UCSF and lead author of the study is quoted as saying.

Dr. Chen and colleagues obtained data for all lung transplant registrants in the U.S. listed between May 4, 2002, and May 3, 2008. They simultaneously examined death versus transplant for the nearly 8,000 registrants diagnosed with COPD, IPF, CF or IPAH, comparing the "Pre-LAS" period (May 4, 2002 to May 3, 2005) to the "post-LAS" (May 4, 2005 to May 3, 2008).

Researchers found that after the implementation of LAS, the risk of death for every individual disease except IPAH decreased significantly.
 
Before the implementation of LAS, the likelihood of transplant was highest for COPD patients and lowest for IPAH patients. After the LAS, IPAH patients remained the least likely to receive a transplant, despite being at greater risk of death while waiting than either COPD patients or those with IPF.

"The fact that the LAS has led to an overall improvement in the time to transplantation is not particularly surprising," noted Dr. Chen. "But we would hope that those changes would have positively affected all lung transplant candidates, whereas we found distinct differences in the impact according to disease, particular for pulmonary arterial hypertension."

A possible explanation is the fact that key prognostic indicators in IPAH are not considered under the LAS. "Hemodynamic variables currently included in LAS, such as pulmonary capillary wedge pressure, provide little information for patients with IPAH," wrote Dr. Chen. "In contrast, mean right arterial pressure and cardiac index, which are known to be strong predictors of mortality for patients with IPAH, are not utilized."

In an accompanying editorial, Kevin Chan, M.D., of the University of Michigan wrote, "The LAS has had a positive impact on the majority of wait-listed patients in the U.S. Although the overall likelihood of transplantation has increased and wait-list mortality has fallen, Chen and colleagues show that patients with IPAH are relatively disadvantaged by the current system. Equity of donor lung allocation in the era of LAS is not quite there yet."

SOURCE: American Journal of Respiratory and Critical Care Medicine, September 1, 2009

Source: Ivanhoe

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