Fetal intestinal oxygen consumption at various levels of oxygenation

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.