Viaspan was the trademark under which the University of Wisconsin cold storage solution was sold. Currently, UW solution is sold under the ViaSpan trademark and several other trademarks. UW solution was the first solution thoughtfully designed for use in organ.
Currently in the U.S. there are over 100,000 patients awaiting kidney or liver transplants with transplant rates of only 20% for kidney and 38% for liver. There is clearly a need to improve both preservation of the organs and to expand the donor pool. The purpose of this article is to review the current methods of preservation for kidneys and livers, including a review of the preservation solutions in clinical use and those undergoing pre-clinical studies.
The main goal in organ preservation is to maintain function of the organ and tissue during storage so that the graft will function at reperfusion. To this end, maintenance of cellular energy must be accomplished. This is done by reducing metabolic demand (and subsequent ATP hydrolysis) by hypothermia. As the temperature of the tissue falls, the metabolic demand drops according to the Arrhenius equation. When cells cool, the ATP utilization falls, as does the work provided by the Na+/K+ ATPase (sodium pump). This pump keeps intracellular sodium low under normothermic conditions. However, when the pump activity falls during hypothermia, the intracellular sodium rises, which pulls water into the cell resulting in lethal cell swelling. Southard described the effects of hypothermia on cell swelling in the kidney and how these effects could be mitigated by using simple cell impermeants.2 Molecules such as saccharides and anions are large enough to leave the capillary and enter the interstitial space but too large or too charged to enter the cell, prevent hypothermiainduced lethal cell swelling by osmotically pulling water out of the cell.
There are currently 2 modes of preservation methods for kidneys and livers: static and dynamic. Simple cold storage (SCS) is the main method for static storage while hypothermic machine perfusion (HMP), normothermic machine perfusion (NMP) and oxygen persufflation (OP) comprise the methods for dynamic preservation. Of these 4 methods, only SCS and HMP are approved clinically for kidneys and only SCS for livers.
New University of Wisconsin organ cooler does not use any ice, but instead relies on a special preservation solution that may be more effective overall. The device can keep the solution within a narrow temperature range, and so preserving the organ as ideally as possible. Because ice is not utilized, the device may even be used with new preservation techniques that keep the organ at body temperature.
New methods require some dynamic movement of either fluid or gas to facilitate preservation. Hypothermic machine perfusion was one of the earliest methods of preservation while normothermic machine perfusion has shown promise in recent years. Venous oxygen persufflation is a method by which gaseous oxygen is bubbled via the blood vessels through the organ and the gas escapes via pin holes at the surface of the organ. The advantage of these methods over simple cold storage is that they all have been shown to improve recovery of Donation after Cardiac Death organs. These organs have the potential to increase the donor pool by 20–40%.