Fetal intestinal oxygen consumption at various levels of oxygenation

Abstract

In seven chronically catheterized fetal lambs, blood flow and oxygen consumption (VO2) in the combined small and large intestines were determined at various oxygen concentrations in fetal arterial blood (CaO2). Intestinal blood flow (Qi) was measured with the radioactive-microsphere technique; intestinal oxygen delivery (DO2 = Qi X CaO2), VO2 [Qi X C(a-v)O2, where oxygen extraction [C(a-v)O2/CaO2] were computed with the Fick equation. Compared with normally oxygenated fetuses (CaO2 greater than 6.6 ml/dl), moderately hypoxemic fetuses (CaO2 = 4.4-6.6 ml/dl) had decreased intestinal DO2, increased oxygen extraction, and no change in intestinal VO2, Qi, or mesenteric-venous pH and base excess. During severe fetal hypoxemia (CaO2 less than 4.4 ml/dl), DO2 decreased further while oxygen extraction increased substantially. Intestinal VO2 dropped, however, because the rise in oxygen extraction could no longer completely compensate for the reduced DO2. With severe hypoxemia, Qi and mesenteric-venous pH and base excess also fell. These data indicate that the fetal intestinal tract is able to meet its oxygen needs during hypoxemia until a critically low level of oxygenation is reached. Below this level intestinal oxygenation becomes inadequate, and anaerobic metabolism ensures.

Effects of Hypoxemia on Gastrointestinal Blood Flow and Gastric Emptying in the Newborn Piglet

“…We have shown that severe hypoxemia in the newborn piglet causes significant decreases in stomach, small intestinal mucosa, and colon blood flow, as well as decreases in oxygen delivery and consumption. These results are consistent with those seen in the ovine fetus (7). These changes most likely reflect the compensatory routing of cardiac output to high priority organs (brain and heart) in the presence of hypoxemia, at the expense of low priority organs such as the GI tract (26,27).…”

“…100 g-I). Edelstone reported similar results in fetal lambs with CaOz 5 4.4 ml/dl (7). In four of seven of our animals, we noted a failure to meet oxidative demands when O2 delivery decreased below a critical level (~2 0 % of baseline values) or O2 extraction did not sufficiently increase (to 263% above baseline values).…”

“…The validity of Cpv02 to represent GI venous samples has been confirmed previously (7,17). Blood flow was expressed as ml .…”

“…This may reflect less intrinsic protection of the mucosa-submucosa against the damaging effects of ischemia. In cases of reduced blood flow and O2 delivery, the fetal and newborn intestinal tract is capable of increasing 02ExGI in order to maintain stable oxygen consumption (6,7). It appears that at critically low levels of 02, this compensatory mechanism is impaired or insufficient and V02GI is reduced.…”

Systemic oxygen transport in patients with congenital heart disease.

“…To date, 02 balance studies in animals and man have focused on normal, physiologic relationships,'-5 the acute pathophysiology of disease states,2' S1 or laboratory manipulations. [12][13][14][15][16][17][18][19][20] From the University of New Mexico School of Medicine, Departments of Pediatrics and Physiology, Albuquerque.…”