Additives To Preservation Solutions

In general, colloid is necessary for machine perfusion, but not for simple storage. Extended preservation times by perfusion require suitable nutritional precursors and oxygen supply. Otherwise, prerequisites for machine perfusion solutions, and for solutions used for cold flushing before hypothermic storage, have been similar. The major requirements have been suitable impermeable solutes (anions or non-electrolytes) replacing permeable chloride, together with a suitable buffer system.

The role of nutrient substrates during static storage, and on reperfusion, is also unclear. Substrates are not obligatory — solutions containing no utilizable metabolic fuel can give excellent preservation of most organs for 24 hours, and in the case of the kidneys, for up to 3 days experimentally with PBS solution. In contrast, substrates capable of supporting anaerobic glycolysis (such as fructose) have been shown to be beneficial in some experimental situations.238

Static storage normally implies anaerobic conditions with progressive fuel depletion. Precursors of ATP added to flushing solutions (such as adenosine, adenine, inosine, and phosphate), ATP itself,239 or high-energy intermediates such as fructose 1,6 bis phosphate240 have been shown helpful in some experiments. Whether these agents are acting by increasing the availability of high-energy compounds or by some other metabolic or hemodynamic manner is uncertain. In contrast, nutritional depletion in experimental conditions can enhance tolerance to ischaemic damage. Glycogen-depleted livers from fasted rats showed resistance to ischemic injury and better survival after transplantation.241

Small concentrations of added agents that quench or scavenge oxygen free radicals, antioxi-dants, calcium-channel blockers, and other pharmacologically or metabolically active compounds can help as adjuvants in increasing ischemic tolerance. In UWs, allopurinol, glutathione and adenosine have been demonstrated to be helpful — insulin and steroids appear of no benefit. Other additives have included cytokines, prostaglandins, leukotrienes, lazaroids (aminosteroids) and their intermediaries, hormones, chlorpromazine and other benzodiazepines, nitric oxide, interleukins, TNF antagonists, and other growth factors.172 For example, prostaglandin analogue (Iloprost) was shown to enhance ATP recovery when added to the cold reperfusion solution in experimental porcine liver preservation130 (see Figure 9.9). Most recently, the addition of a mixture of trophic factors during cold preservation has shown promise in experimental work.242

Storage-reperfusion injury affects endothelial cells and activates neutrophils and macrophages (e.g., Kupffer cells in liver). This injury leads to the expression of cell adhesion molecules, leukocyte and platelet adhesion, and exacerbation of reperfusion injury. Kupffer cells are a main source of oxygen radicals and also release other proinflammatory mediators, such as TNF-a, interleukins 1 and 6, eicosanoids, and nitric oxide. Agents suppressing TNF-a formation include calcium channel blockers, pentoxifylline, adenosine, and prostaglandin E, whereas liposaccharides from bacteria are stimulatory.172

Time (minutes)

FIGURE 9.9 Changes within ATP following hypothermic reperfusion with Iloprost. Absolute changes associated with ATP following liver storage (X), hypothermic reperfusion (HtR) (Y), and cessation of HtR (Z); controls (O); and Iloprost (•). Changes are normalized to total phosphorous signal, which remains constant throughout the experimental protocol, and are shown as mean ± SE, n = 5. A greater efficiency for ATP resynthesis was seen with inclusion of Iloprost.

Time (minutes)

FIGURE 9.9 Changes within ATP following hypothermic reperfusion with Iloprost. Absolute changes associated with ATP following liver storage (X), hypothermic reperfusion (HtR) (Y), and cessation of HtR (Z); controls (O); and Iloprost (•). Changes are normalized to total phosphorous signal, which remains constant throughout the experimental protocol, and are shown as mean ± SE, n = 5. A greater efficiency for ATP resynthesis was seen with inclusion of Iloprost.

9.12 STORAGE TEMPERATURE

Organs surrounded by preserving solution and stored and transported in a container of crushed ice maintain a storage temperature of melting ice (0°-2°C). Storage temperatures above 0°C aim to diminish cold-induced membrane paralysis while maintaining the protective effects of hypothermia. Temperatures above 15°-20°C have usually been considerably less effective than 0°C. Temperatures for continuous perfusion have been maintained between 4°C and 10°C. The optimal storage temperature of nonparenchymal cells may differ from that required by parenchymal cells, perhaps over quite a narrow range. In rat liver preservation, 48-hour storage was possible by simple hypothermic storage at 4°C but not at 0°C.243 Differences in effectiveness between various solutions (UW, sucrose, citrate) were less marked during storage at 4°C than at 0°C.

These results indicate a greater sensitivity of endothelial cells to cold damage than occurs with parenchymal cells, and temperatures around 4°C may be optimal for hypothermic storage.172 Storage at 4°C could be simply obtained by the portable electrical refrigerator storage of organs surrounded by cold liquid rather than by ice, but this would require good temperature control within the system, as air is a poor conductor of heat. Such equipment has been used in experimental studies244 but not clinically examined yet to any great degree.

9.13 PRE-REPERFUSION RINSE SOLUTIONS

A prevascularization flush-out or rinse at the conclusion of the storage period, just before reimplantation, has two main aims: first, to remove potentially toxic components of the preservation solution and accumulated waste products (e.g., high levels of potassium and hydrogen ions) or to prevent a large intracardiac bolus of cold fluid on clamp release. Second, rinsing aims to smooth the transition between hypothermic storage and isothermic revascularization. Anastomosis can be tested before revascularization by intravascular wash-out before final clamp release. This process has been most studied in relation to the liver. One method allows blood to flow to the liver via the portal vein, venting the initial effluent from the infrahepatic vena cava before completing this anastomosis, and finally releasing the clamp on the suprahepatic vena cava. Alternatively, the organ

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