This retrospective study presents the long-term outcome of 25 consecutive patients receiving BLTx in a low-volume center. This report demonstrated that the satisfactory outcome can be achieved using the urgency-based organ allocation criteria in a donor-scare country.
According to the TORSC report, the average annual organ donation rate after brain death in Taiwan was around 6.5 per million of population (PMP) in recent years, which is far below that of Spain (35.3 PMP), Belgium (30.1 PMP), Portugal (28.1 PMP), the U.S.A. (25.6 PMP) and France (25 PMP). The low donation rate in Taiwan creates a severe shortage of donor lungs and limits the annual number of LTx. Ample evidence now exists confirming a relationship between surgical outcome and volume of the procedure, which becomes especially important for complex procedures such as transplantation [3-6]. Weiss et al. reported that the cumulative risk of mortality at 30 days, 1 year, and 5 years after LTx was highly dependent on volume. In general, high-volume centers (those centers achieving an average of 20 LTx per year) had superior short- and long-term outcomes, and low-volume centers (those centers achieving less than 10 LTx per year) have alarmingly high mortality rates. In Taiwan, none of the seven authorized LTx centers have been able to reach 10 LTx per year due to the low organ donation rate. Based on these findings, it is easier to understand why the official report of national LTx outcomes in Taiwan is worse than those reported by the ISHLT. Interestingly, some low-volume centers have been able to produce excellent outcomes, implying that factors influencing mortality after LTx are far more complex than simply volume. Weiss et al. speculate that low-volume centers may be able to provide similar outcomes as the high-volume centers if they are equipped with specialized staff, integrated patient support systems, and a culture of excellence. These characteristics provide a benchmark for LTx centers to strive for, no matter the size or volume of the center.
The other important issue that significantly impacts transplant outcomes is the organ allocation system. The new allocation rules implemented in France since 2007, which prioritize allocation of donor lungs to candidates with conditions posing an immediate threat to life, are similar to those in Taiwan. The national LTx report from France demonstrated that the survival results for emergency LTx (ELTx) were worse than those for non-urgent LTx [7]. Survival rates in the ELTx group were 64.5% and 55% at 1 and 2 years, respectively, which were significantly lower than the regular, nonurgent LTx group (77% and 71%, respectively). As with France’s experience, Spain and the United States also have similarly poor outcomes for emergent or urgent LTx [8,9]. According to the United Network for Organ Sharing (UNOS) data, patients on MV or ECMO before LTx had decreased survival after LTx [10]. The 1-year survival associated with ventilator and ECMO support groups were 67.7% and 57.6%, respectively, which were both inferior to those in the high lung allocation score group. Based on these findings, it is reasonable to conclude that this kind of urgency-based allocation policy may contribute to futile and unsuccessful transplantation, especially for low-volume, limited experience LTx centers in donor-scare countries, such as those in Taiwan.
Our report is consistent with the conclusion that lung allocation policy has great influence on the distribution of underlying disease indications for LTx. Although COPD was one of the major diagnoses for LTx in the UNOS and ISHLT reports, only one patient with COPD (4%) received LTx in our study population [1,11]. This unique phenomenon may result from the urgency-based lung allocation system in Taiwan. These allocation rules could potentially make access to LTx more difficult for patients not fulfilling the emergency criteria when donor lungs are scarce, gradually leading to an increase in waiting-list mortality for non-urgent patients, such as those with COPD.
In this study, eighteen (72%) patients were already dependent on MV or ECMO support prior to LTx. In order to provide adequate hemodynamic support during LTx, ECMO was used preferentially as an alternative to cardiopulmonary bypass (CPB). We prefer the ECMO circuit to assist LTx instead of CPB for several reasons. First, modern ECMO technology, including replacement of silicone oxygenators, the introduction of heparin-bonded circuits, and new centrifugal pumps, gives ECMO the capacity to support gas exchange without the need for high-dose heparin administration or anticoagulation therapy. Second, our institution is one of the highest-volume ECMO centers in the world. In our institution since 1994, more than 1,950 patients have been treated with ECMO for sundry causes of cardiopulmonary collapse. Therefore, the refined technical aspects of ECMO combined with the experience using ECMO in our hospital significantly decreases the incidence of major ECMO-attributed complications, including bleeding and peripheral access-related limb ischemia, in our transplant population. Finally, ECMO can provide a bridge to transplantation in patients unresponsive to maximal pulmonary-respiratory support [12-15]. In this report, of 23 patients (92%) receiving BLTx under ECMO support, only one needed to switch to traditional cardiopulmonary bypass (due to severe hemodynamic instability). Furthermore, ECMO allowed 3 (12%) patients cardiopulmonary failure to be stabilized before LTx and thus be successfully bridged (up to 86 days) to BLTx in a high-urgency setting; each of these patients was weaned off ECMO smoothly and discharged without any complications.
The 1-, 3-, and 5-year survival rates after BLTx in this study are similar to those of the Japanese registry report (86%, 79%, and 73%), and are slightly superior to those from UNOS (84%, 66%, 51%) and ISHLT (79%, 64%, 53%) [11,16,17]. Given the small sample size in our study, we can only speculate on the reasons for our improved outcomes. Most likely, a combination of specialized staff, operative technique, and optimal recipient-donor matching (100% cross match and race matching, and only 4% CMV mismatching) is responsible for these outcomes; however, further investigation of these trends is warranted to confirm this speculation.
This study is limited by its single-institution, small sample size, and retrospective nature. Moreover, there was no control group to reduce the influence of selection bias. However, a control group may present ethical challenges because LTx is a promising, feasible and lifesaving procedure for patients with end-stage pulmonary disease.