Table 2.

A table showing risk factors for ECMO-BTT, including relevant references. The risk factors are separated into major risk factors of substantial risk and less major risk factors which may be mitigated and accepted

Risk factor	Comment	References
Major risk factors
Retransplantation versus first transplantation	Patients bridged to second transplantation have a substantially reduced survival compared with primary transplant recipients.	Hoetzenecker et al. (2018) [8••]
Additional organ system dysfunction	Patients with other organ dysfunction, such as liver or kidney dysfunction, carry an increased risk of morbidity and mortality. Certainly, irreversible organ dysfunction should be strongly considered as a contra-indication to BTT	Tipograf et al. (2019) [9••] Kukreja et al. (2020) [19]
Deconditioning	Quantifying the level of deconditioning is difficult. However, the higher the potential for deconditioning during the bridging period, the higher is the incidence of CIM postoperatively. Participating in physical therapy may mitigate the risks associated with deconditioning during BTT	Rehder et al. (2013) [7•] Hoetzenecker et al. (2018) [8••] Tipograf et al. (2019) [9••] Hakim et al. (2018) [10] Hayes at el. (2016) [11]
Minor risk factors
Type of ECMO-BTT	Venovenous ECMO is associated with improved survival compared with more advanced support. VA-ECMO denotes a more critically-ill patient, and naturally, suggests less success	Kukreja et al. (2020) [19]
Center volume/experience	Centers with more experience with lung transplants and ECMO are likely to have greater success using ECMO as BTT. This is true with more complex patients that require more advanced ECLS.	Hayes et al. (2016) [11] Langer et al. (2019) [18] Hayanga et al. (2016) [20] Halpren et al. (2019 [21])
Length or bridging period	The length of the bridging period is associated with mixed results in the literature. A period of greater than 30 days may be associated with less success.	Crotti et al. (2013) [6] Langer et al. (2019) [18]
Underlying disease process	Patients with cystic fibrosis may have a survival advantage over other diseases. Conversely, patients with interstitial lung disease may have worse outcomes.	Lafarge et al. (2013) [22]
Infection	Patients with suppurative lung disease, such as cystic fibrosis, can be safely bridged with ECMO. However, infection with certain organisms, such as Achromonavter, may be challenging to treat with indwelling intravenous cannulae	Biscotti et al. (2015) [23]