To the Editor:
Shukrallah et al.1 describe the use of donor aorta as an adjunct conduit to facilitate pulmonary artery cannulation for ex vivo lung perfusion (EVLP). As challenges pertaining to cannulation are inherent to EVLP, the article provides helpful practical content, but only considers cannulation challenges related to the pulmonary artery, and offers just a single solution that may not always suffice.
In prior EVLP studies, we recognized lung cannulation challenges at both the pulmonary artery and atrial cuff and developed several novel cannulation strategies, which have been extensively described in methods and supplementary sections https://links.lww.com/ASAIO/A752.2,4–6 In ex vivo lungs, a shortened main pulmonary artery can be managed with a donor artery, vein, and/or synthetic (e.g., Dacron) graft.2 In the absence of a main pulmonary artery, donor aorta can be fashioned end-to-end to bridge the left and right pulmonary arteries, then a second graft can be anastomosed end-to-side to the donor aorta to serve as the inflow conduit (Supplemental Figure 1A https://links.lww.com/ASAIO/A752).
Although optimal cannulation and perfusion strategies remain to be determined, configurations with a closed atrium have been shown to result in less edema and enhanced lung physiology.3 For EVLP circuits with a closed atrium, a shortened atrial cuff can be reconstructed using donor pericardium (Supplemental Figure 1B https://links.lww.com/ASAIO/A752), vein, or commercial soft tissue or pericardial patch products, thus enabling connection to the circuit. While many protocols use collared polymer tubing, we previously described2,4–6 the use of donor vessel as an organ-to-circuit “bio-bridge” (Supplemental Figure 1C https://links.lww.com/ASAIO/A752) to facilitate venous drainage and enable: (1) tight regulation of vascular flow, (2) consistent maintenance of pulmonary venous drainage despite differing anatomy and distribution of pulmonary veins across studies, (3) optimal placement of ex vivo lungs in prone or supine position, and (4) evaluation of oxygenation and ventilation separately in left and right lungs.4 To better understand flow characteristics through the bio-bridge, we performed computational fluid dynamics modeling, which indicated smooth laminar flow through the bio-bridge into the venous drainage cannula (Supplemental Figure 1D https://links.lww.com/ASAIO/A752).6 Immunohistochemical staining confirmed that the endothelium of the bio-bridge was intact and viable after 36 hours of normothermic cross-circulation EVLP.6 Based on these and other studies, we posit that use of the donor vessel bio-bridge as a natural vascular conduit between the organ and circuit confers demonstrable advantages due to: (1) non-thrombogenic surface and (2) intrinsic elasticity, which provides vasoprotective capacitance to dampen abrupt changes in circuit pressures.4
After more than a decade of clinical practice, the EVLP field has made remarkable progress, but still lacks standardization not only in cannulation techniques but also across platforms (e.g., commercial, custom), circuit configurations (e.g., open, closed atrium), perfusates (e.g., acellular, cellular), flow and ventilation settings, and reported parameters and outcomes. In the future, consensus guidelines should be established to help standardize cannulation and perfusion techniques and data reporting in order to facilitate rigorous cross-study comparisons and inform best practices.
1. Shukrallah B, Ganapathi AM, Whitson BA: Donor aorta as conduit for ex vivo lung perfusion. ASAIO J. 67: e182–e183, 2021.
2. Hozain AE, O’Neill JD, Pinezich MR, et al.: Xenogeneic cross-circulation for extracorporeal recovery of injured human lungs. Nat Med. 26: 1102–1113, 2020.
3. Linacre V, Cypel M, Machuca T, et al.: Importance of left atrial pressure during ex vivo lung perfusion. J Heart Lung Transplant. 35: 808–814, 2016.
4. Guenthart BA, O’Neill JD, Kim J, et al.: Regeneration of severely damaged lungs using an interventional cross-circulation platform. Nat Commun. 10: 1985, 2019.
5. Guenthart BA, O’Neill JD, Kim J, Fung K, Vunjak-Novakovic G, Bacchetta M: Cell replacement in human lung bioengineering. J Heart Lung Transplant. 38: 215–224, 2019.
6. O’Neill JD, Guenthart BA, Kim J, et al. Cross-circulation for extracorporeal support and recovery of the lung. Nat Biomed Eng. 1: 0037, 2017.