By Ramsey Hachem, M.D.
Washington University School of Medicine Barnes-Jewish Hospital
Division of Pulmonary and Critical Care
February, 2006
Approximately one half of the 1700 lung transplants performed annually worldwide are single lung transplants. This raises an important question in the field of lung transplantation: should patients receive one lung or two? A simple answer might be that if one lung is good for you, then two would be better. But is the answer quite so straightforward? An alternative approach might be that if one lung is sufficient, then one donor could donate a lung to two recipients and expand the donor pool thus shortening the waiting time for transplantation. But is one lung sufficient? In kidney transplantation, one donor donates a kidney to two recipients and a single kidney transplant is sufficient. Similarly, in living lobar liver transplantation, a living donor donates a part of their liver, which provides the recipient with adequate liver function. Likewise, single lung recipients have sufficient lung function to improve their exercise capacity substantially and no longer need supplemental oxygen.
However, certain lung diseases require a bilateral transplant. Patients with cystic fibrosis, and bronchiectasis in general, need bilateral transplants because the chronically infected remaining lung would infect the transplanted lung. In addition in recent years, the majority of patients with pulmonary hypertension have received bilateral transplants. The pulmonary physiology of a single lung recipient with pulmonary hypertension is unique; the high blood pressure in the native lung diverts nearly all of the blood flow to the transplanted lung, but airflow is evenly distributed between both lungs. Furthermore, while the transplanted lung can adequately manage the additional blood flow, complications in the graft, such as pneumonia or rejection, can result in severe hypoxemia (very low blood oxygen levels). Nonetheless, single lung transplantation was the preferred operation for patients with pulmonary hypertension until approximately 10 years ago. Indeed, patients with pulmonary hypertension who had a single lung transplant have similar survival results to those who had a bilateral transplant. However, most centers today choose a bilateral transplant for patients with pulmonary hypertension; 88% of patients with pulmonary hypertension reported to the International Society for Heart and Lung Transplantation (ISHLT) Registry had a bilateral transplant in 2003.
But, what about patients with emphysema, pulmonary fibrosis, or sarcoidosis? Should they receive one lung or two? This has been a controversial topic and most programs have their own preferences. Proponents of bilateral transplantation argue that two lungs provide additional lung reserve when complications, such as chronic rejection, arise. On the other hand, proponents of single lung transplantation argue that the donor pool can be expanded which might reduce mortality on the waiting list and waiting times for transplantation. Unfortunately, no prospective randomized studies have been performed to address this issue, and the only available data comes from large registries of lung transplantation, such as the ISHLT Registry and the United Network for Organ Sharing (UNOS) Registry. Unfortunately, while registry data provides large sample sizes for analysis, they often lack important information. Nonetheless, when the survival of bilateral recipients with emphysema, or COPD, is compared to that of single recipients, it is apparent that their survival is significantly better than single recipients. However, this type of single variable analysis does not account for other potentially important variables that might impact survival such as recipient age, co-morbidities, and severity of illness. In fact, there are often certain clinical factors that influence the choice of operation (single or bilateral transplant) for a particular individual that are not accounted for in registry analyses. For example, because single lung transplantation is typically a shorter operation and easier to recover from, many single recipients are sicker, frailer, or older. Furthermore, patients with pulmonary fibrosis who have a single lung transplant have similar survival results as those who have a bilateral transplant. The explanation for this finding is unclear from the registry data and no studies have been performed to investigate this further.
So what’ll it be? One lung or two? This remains an unanswered complex question. Obviously, some patients need to have a bilateral transplant, but a single lung is often sufficient for many others.