Studies in perfusion hypothermia with special reference to “deep hypothermia” and circulatory arrest

Abstract

Summary o 1. Perfusion hypothermia produces large temperature gradients within the body since organs are cooled roughly in proportion to their basal blood flows. The difference between the coldest and the warmest portion of the body after 30 minutes of perfusion exceeds 25° C. 2. The average body temperature, which provides a proper measure of total body cooling, may be calculated from the arteriovenous temperature difference and the extracorporeal flow rate. 3. True “deep” hypothermia is not obtainable by reasonable periods of perfusion alone. 4. An important rise of core temperatures occurs during circulatory arrest in hypothermia because of the relatively high average body temperature. 5. High average body temperatures lead to continuing production of lactic acid in muscle tissue, whereas low core temperatures impair lactic acid metabolism. Thus metabolic acidosis is progressive in prolonged perfusion hypothermia, and is accentuated by total circulatory arrest. Progressive acidosis may be minimized by uniform profound cooling by combining external with perfusion hypothermia. 6. Diluents appear to have little effect on total body heat exchange during perfusion cooling. 7. Perfusion warming has a differentially greater effect on core organs. Though these are readily brought to a normal range, much of the animal may remain cold.