Effects of hetastarch and mannitol on prolonging survival in stable hypothermia in rats

In rats, prolonged stable hypothermia (similar to 24 h at body temperature of 19 degrees C) is characterized by a time-dependent increase in hematocri t, plasma osmolality, and red blood cell fragility and a decrease in plasma volume. These changes impede tissue microcirculation and could limit survi val. As a countermeasure, we used plasma volume expanders of both long (het a-starch)- and short-lasting (mannitol) characteristics to improve microcir culation and hopefully hypothermia survival. Infusion of 6% hetastarch at h our 3 in hypothermia significantly (P < 0.05) enhanced survival over saline control(33.5 vs. 23.8 h); a significant delay in the increases of hematocr it and cell fragility was also observed compared with those in saline contr ols. Treating the animal with 6% hetastarch at hour 20 during hypothermia c aused a similar but less-effective improvement in survival. In contrast, tr eating the rats with 6% mannitol at hour 3 or 20 during hypothermia failed to enhance survival over saline control, although transient improvement in plasma volume was observed. Our results indicate that by using a long-lasti ng volume expander, which tends to better maintain plasma volume and rheolo gical parameters governing microcirculation than does saline or a short-las ting volume expander, hypothermia survival can be significantly improved.