Circulatory effects of profound hypothermia during extracorporeal circulation

¹ Cardiology Branch, National Heart Institute, National Institutes of Health, Bethesda, Maryland

The effects of hypothermia on peripheral vascular resistance, venous return, and systemic blood volume were studied in dogs using extracorporeal circulation and a constant systemic perfusion rate. Cooling to 15–20 C produced a significant fall in total systemic peripheral vascular resistance and a large augmentation of systemic blood volume. The latter was superimposed on the gradual increase in systemic blood volume which occurs in many dogs on cardiopulmonary bypass. Both systemic vascular resistance and blood volume returned toward control levels during rewarming. Indicator dilution curves demonstrated a decrease in the "actively" circulating blood volume despite the observed increase in total systemic blood volume. These observations suggest that during hypothermia significant arteriolar dilatation occurred and that substantial volumes of blood were "trapped" in the peripheral vascular bed. This trapping resulted in the striking decrease in venous return and increase in systemic blood volume.

Note:
With the Technical Assistance of Robert M. Lewis