The effect of surface cooling on blood flow distribution in infant pigs with mature left to right shunts.

Surface cooling as an adjunct to cardiopulmonary bypass, core cooling, and circulatory arrest has been effectively used to produce more homogeneous cooling and better tissue preservation. A previous study, using pigs with newly created aortopulmonary shunts, revealed a redistribution of blood flow away from the kidneys and viscera during surface cooling that did not occur in normal pigs. The present study tests the hypothesis that pigs with mature aortopulmonary shunts behave in a similar manner. Group I (N = 7, unshunted pigs) and Group II (N = 7, shunted pigs) underwent surface cooling and blood flow distribution measurements by microspheres at 37, 32, 28, and 25 degrees C. Both Groups I and II experienced a decrease in cardiac output with hypothermia. Group II had decreased absolute tissue flow to the viscera, kidneys, muscle, and skin at 37 degrees C compared with Group I, even before the onset of hypothermia. During hypothermia, Group I experienced a decrease in all tissue flows, but Group II had a decrease only in visceral and renal flows at 25 degrees C. Blood flow distribution, as a percentage of cardiac output, showed little change (decrease only in skin) in Group I with hypothermia. In Group II, however, a maldistribution of cardiac output developed resulting in decreased percentage of cardiac output to the kidneys and viscera and an increased percentage of cardiac output to the lungs that was confirmed by an increase in the Qp/Qs ratio.(ABSTRACT TRUNCATED AT 250 WORDS)