Blood flow distribution in infant pigs subjected to surface cooling, deep hypothermia, and circulatory arrest: Deleterious effects in pigs with left-to-right shunts

Abstract

Surface cooling, deep hypothermia and circulatory arrest have been used effectively for correction of congenital heart defects in infancy. Which patients are best suited for this technique has not been addressed. The addition of surface cooling to deep hypothermia and circulatory arrest provides homogeneous cooling and avoids swelling due to reperfusion injury after circulatory arrest. However, surface cooling in patients with large left-to-right shunts causes increased peripheral resistance and increased shunting which can result in decreased perfusion of vital organs. The purpose of this study is to measure the effect of a large left-to-right shunt on total organ blood flow distribution in infant piglets during surface cooling, deep hypothermia, and circulatory arrest. Eleven 2-week-old piglets had surface cooling, deep hypothermia, and circulatory arrest for 45 minutes, followed by rewarming and weaning from cardiopulmonary bypass. Microspheres (15 mu) were injected before surface cooling, at 28 degrees C, at 15 degrees C, and after weaning from cardiopulmonary bypass. Group I (five piglets) was the control. Group II (six piglets) had a large (6 mm) left-to-right aortopulmonary shunt established before microsphere injection. Cardiac outputs in both Groups I and II decreased with surface cooling. The distribution of cardiac output in Group I did not change with surface cooling; however, Group II pigs showed marked change in distribution of cardiac output, resulting in decreased renal, visceral, and pulmonary flow (p less than 0.05). Amylase determinations before and after surface cooling, deep hypothermia, and circulatory arrest were unchanged in Group I but elevated in Group II (p less than 0.05). These observations suggest altered cellular metabolism in visceral organs during the period of surface cooling which may be compounded by circulatory arrest and rewarming.