All seven patients who received lung transplants using Oxy-RVAD using ECMO as BTT were discharged without serious side effects associated with ECMO. This outcome suggests the feasibility of Oxy-RVAD using ECMO as a BTT in patients who develop RVHF with V-V ECMO.
Many lung transplantation candidates require invasive mechanical ventilation and ECMO support while on the waiting list(9). In these patients, complications associated with ECMO and deterioration of their lung condition can result in RVHF leading to hemodynamic instability, multiple organ failure, and a poor prognosis. There are several current therapies for right heart decompensation including fluid optimization, inotropes, adjustment of ventilator settings, and inhaled nitric oxide. However, these may not be sufficient for patients with hemodynamic instability and, in such patients, mechanical support may be required.
Considering hemodynamic instability of lung transplantation candidates with RVHF during V-V ECMO, hemodynamic stability should be maintained longer, and with fewer complications, when associated with ECMO. Additionally, ECMO should not interfere with the patient’s rehabilitation, as muscle strength is one of the major factors associated with successful lung transplantation outcomes(10). Oxy-RVAD using ECMO, has several advantages and can provide a successful BTT. Oxy-RVAD using ECMO is more physiologic, can prevent right ventricular distension, preserve transpulmonary blood flow, and prevent peripheral arterial cannula complications such as limb ischemia and Harlequin syndrome(11, 12). In addition, it has been reported that there are fewer thromboembolic complications with Oxy-RVAD than V-A ECMO(12). Furthermore, the main pulmonary artery tissue at the cannula insertion site is firm, allowing the cannula to be maintained for an extended period of time(11). The position of the ECMO cannula does not affect lung transplantation surgery, and the main pulmonary artery cannula has the advantage of being used as the drain cannula during lung transplantation surgery. Finally, rehabilitation with Oxy-RVAD using ECMO is easier when compared to peripheral V-A or V-A-V ECMO(13).
Only a few studies have reported using Oxy-RVAD using ECMO for BTT. Lee et al. reported on Oxy-RVAD using ECMO as a BTT. Their successful lung transplantation rate was 10/14 (71.4%), 9/10 (90%) of the patients who underwent transplantation were discharged, the total ECMO application period was 21.5 days, and the average Oxy-RVAD using ECMO application period was 8 days. Their 1-year survival rate was 8/10 (80%)(14) (Table 3). These results are similar to this study. Taken together, these two studies suggest that Oxy-RVAD using ECMO as a BTT in patients with RVHF is safe and feasible.
V-AV or V-A ECMO can immediately correct hemodynamic instability caused by RVHF. However, these techniques have several limitations. In the terminal stage of lung disease, it can be difficult or impossible to properly control the flow of V-AV ECMO, because the reinfusion cannulas are located in the artery and vein respectively. The disadvantages of peripheral V-A ECMO are distal limb ischemia, compartment syndrome, retroperitoneal hemorrhage, poor upper body oxygenation, and difficulty in performing rehabilitation for lung transplantation patients. Additionally, the duration of ECMO is short, and the ability to perform rehabilitation is difficult (Table 3).
Applying central V-A ECMO, Chicotka et al.(5), reported a successful lung transplantation rate of 64.5% (20/31) with a mortality rate during ECMO of 35.4% (11/31). The average duration of ECMO was 26.1 days. Our previous study also showed a transplant success rate of 66.6 % with a mortality rate during ECMO of 33.3%. The average duration of ECMO was 11 days(7). Taken together, it appears that Oxy-RVAD using ECMO is noninferior compared to V-A ECMO as BTT, in terms of the duration of ECMO, the success rate of lung transplantation, and the mortality rate during ECMO.
Rehabilitation during the waiting period for a lung transplant is an important factor in the success of the procedure, and it is important that ECMO does not interfere with rehabilitation in patients who have undergone ECMO as BTT. The proportion of patients who underwent rehabilitation with a peripheral ECMO reinfusion cannula inserted into the femoral artery was 28% (2/7) in a study by Hoetzenecker et al.(15) and 33% (2/6) in the study by Ius et al(16). For central ECMO, where the reinfusion cannula was inserted into either the axillary or innominate artery, 77% (24/31) of the patients underwent rehabilitation(6). In Lee et al.’s study applying Oxy-RVAD using ECMO as BTT, 14/14 (100%) of the patients received rehabilitation as did (7/8) 87% of the patients in this study(14). It appears that central ECMO or Oxy-RVAD using ECMO may be more advantageous than peripheral ECMO for allowing rehabilitation, an important factor for successful lung transplantation (Table3).
There are, however, complications and disadvantages to Oxy-RVAD using ECMO. In a previous study, Lee et al. found a 21.4% (3/14) incidence of pulmonary congestion and 7.1% (1/14) incidence of infection(14). This study noted minor bleeding around the cannula inserted into the main pulmonary artery, but no patient experienced pulmonary congestion. When Oxy-RAVD using ECMO is performed, blood from the right ventricle and ECMO flow into the lungs and as the amount of blood to the lungs increases, there is an increase in pulmonary arterial pressure(17). In patients with severe pulmonary hypertension, increased pulmonary arterial pressure can lead to pulmonary hemorrhage and edema(18). Therefore, it may be useful to minimize this flow to maintain hemodynamic stability and to reduce the complications of pulmonary hemorrhage and edema.
Limitations of this study include its small sample size, its retrospective nature, and being conducted in a single center. Future studies on the safety and effectiveness of Oxy-RVAD using ECMO as a BTT should be prospective and multicenter to include a large sample population. Lastly, because only a few studies on ECMO for BTT with RVHF have been reported, there are limitations in the comparisons of various types of ECMO.