Cardiopulmonary Bypass And Procurement

Finally, as mentioned in the section on "Lung Preservation", distant organ procurement for heart and lung transplantation can be accomplished by the induction of profound hypothermic circulatory arrest afforded by cardiopulmonary bypass. In the Harefield experience, blood cardioplegia is administered prior to harvesting the heart-lung block which has been cooled to 8°C. The heart-lung block is stored in hypothermic donor blood for transport. Although much more cumbersome than preservative flush-storage, this technique was simplified by the advent of portable cardiopulmonary bypass.34

Perfusate-Storage Vehicle

During organ procurement and storage, ATP depletion and subsequent decreased activity of Na+-K+ ATPase allows an influx of extracellular Na+, Ca2+ and water, an efflux of intracellular K+ and Mg2+, with myocyte edema formation. Adenosine derived from the catabolism of ATP is further metabolized to xanthine and hypoxanthine, prerequisites to the formation of oxygen free radicals during the oxidative respiratory burst following reperfusion. Additionally, the intracellu-lar adenylate pool decreases as nonphosphorylated nucleotide precursors freely cross the cell membrane and escape into the extracellular mileu. A goal of all preservation solutions currently in clinical use is the prevention of this untoward ionic redistribution.35

The ideal perfusate for the induction of cardioplegic arrest and subsequent preservation is uncertain. The optimal ionic composition is partially temperature dependent, as well, in order to avoid the paradoxical effects of totally acalcemic solutions.36 Blood contains physiologic concentrations of calcium as well as an extracellular type ionic composition. Blood based cardioplegia strategies support the notion that blood is an excellent physiologic vehicle with favorable oncotic, buffering, antioxidant, substrate delivery, and oxygen transport capabilities, is readily available and is superior to crystalloid asanguinous cardioplegia.37 An attempt to modify intracellular preservation solutions (e.g., St. Thomas, Euro-Collins) by the addition of impermeants, oncotic agents, metabolic substrates, ATP precursors and antioxidants was the goal of the development of the UW solution, in an effort to mimic the favorable effects of blood.

Although there continues to be regional variation worldwide over the preferred perfusate for simple flush-storage, the balance of clinical series and experimental reports favors intracellular solutions, specifically the University of Wisconsin solution, over other extracellular solutions.38 Nonetheless, a number of studies have used UW solution bases with single compound deletions, substitutions, or additions in an attempt to identify the importance of the different components to clinical heart transplantation.39-42

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