Blood Flow and Oxygen Delivery to the Organs of the Neonatal Lamb as a Function of Hematocrit

Abstract

ABSTRACT. We chronically catheterized 15 newborn lambs (9.5 ± 2.8 days) and measured the distribution of cardiac output by the radionuclide-microsphere technique at hematocrits ranging from 10 volumes % to 55 volumes %. Seven animals were made progressively anemic and eight polycythemic by means of exchange transfusions. Cardiac output and heart rate increased with decreasing hematocrit while whole body oxygen consumption showed a small decrease during severe anemia. Both cerebral and cardiac blood flow markedly increased during anemia which assured a relatively stable oxygen delivery to both organs. The changes seen for blood flow to the carcass (skin, bones, and muscle) were predictable from the effects of blood viscosity: small decreases in flow at the highest hematocrits and small increases in flow at the lowest hematocrits. Consequently, oxygen delivery was as low as 1 ml of oxygen/min/100 g at a hematocrit of 10 volumes %. Renal blood flow remained unchanged while oxygen delivery fell when hematocrit was decreased. Hepatic oxygenation was measured using a modification of the Fick principle. Hepatic blood flow showed only a small decrease as hematocrit increased and changed minimally during anemia resulting in a falling delivery of oxygen with anemia. A stable hepatic oxygen consumption was assured by a marked increase in oxygen extraction during anemia. Two differing organ responses to changes in hematocrit can be seen in the newborn: the brain and heart vary blood flow to assure an adequate delivery of oxygen while a number of other organs show less blood flow regulation and, most likely, vary oxygen removal from blood. Over a wide range of hematocrits, compensatory responses occur in the newborn which effectively prevent the development of tissue hypoxia.

Log in or create a free account to read this content

Gain free access to this article, as well as selected content from this journal and more on nature.com

Access through your institution

or

Sign in or create an account

Continue with Google

Continue with ORCiD