Optimal flow rates during ex-vivo lung perfusion (EVLP)?

Over the last twenty or thirty years, a wealth of literature has been generated on attempts to define the optimal guidelines for temperature, flow, pressures and other evaluation phase parameters during ex-vivo lung perfusion (EVLP). Optimal flow rates in particular have ranged from 20% to 100% of cardiac output although no comparative studies seem to have conclusively shown any difference in post-transplant outcome.

Most of the many studies on optimal EVLP parameters, however, tend to support a flow rate corresponding to 40% of cardiac output (CO), although 100% of CO has been successfully used in the Lund protocol for many years. Occasionally, even flow rates as low as 20% of CO have been evaluated.

One such rather limited experimental study was recently published ⁽⁸⁾ in which porcine lungs donated after circulatory death (DCD) were subjected to EVLP for four hours at flow rates of either 20% or 40%. The lungs were then transplanted and followed for a further four hours.

After transplant, left lung-specific pulmonary vein partial pressure of oxygen was significantly higher in the low-flow group at three and four hours of reperfusion. The authors claim that their low-flow protocol improved lung function, reduced edema, and attenuated inflammation after transplant. Although the study is interesting there appear to be too many limitations to draw conclusions: there were only four pigs in each group, the warm ischemic times were exceptionally long, and there was no cold preservation time. We do not yet know if there is a cost to low-flow in a human setting.

References:

8. Beller JP et al, Reduced-flow ex vivo lung perfusion to rehabilitate lungs donated after circulatory death J Heart Lung Transplant. 2020 Jan;39(1):74-82. doi: 10.1016/j.healun.2019.09.009. Epub 2019 Sep 18. (link to abstract) 

Xvivo Insights PB-2020-02-27