Comparison of the effect of asphyxia, hypoxia, and acidosis on intestinal blood flow and O₂ uptake in newborn piglets

The aim of our study was to compare the effects of asphyxia and the two components of asphyxia, i.e. hypoxia and acidosis, on intestinal blood flow and oxygen consumption in anesthetized newborn piglets less than 3 days old. The first series of experiments, consisting of four groups of piglets, showed that blood flow to the proximal and distal small intestine and colon (as determined by the microsphere technique) significantly decreased after piglets were subjected to a sustained hypoxic hypoxemia (Pa02 50% of control) or asphyxia (acidosis plus hypoxia) for 90 min. A sustained acidosis (arterial pH — 7.0-7.15 for 90 min), however, decreased blood flow only to the proximal small intestine, and sham operation did not significantly alter any intestinal blood flow. All animals subjected to asphyxia and two of five of the animals subjected to hypoxia alone in this series, produced gross and microscopic intestinal lesions similar to those seen in human newborn with necrotizing enterocolitis. Acidosis alone, however, did not produce any pathologic lesions. The second series of experiments showed that the 90-min hypoxic hypoxemia decreased blood flow to both the mucosa and muscularis layers of the small intestine. The third series of experiments, consisting of four groups of piglets, determined the effects of 60-min acidosis, hypoxic hypoxemia, asphyxia, or sham operation on venous outflow and oxygen consumption of the isolated in situ terminal ileum. Acidosis or sham operation altered neither ileal blood flow nor oxygen consumption. Hypoxia or asphyxia, however, decreased ileal oxygen consumption without significantly decreasing blood flow. Our study indicates that hypoxia, a component of asphyxia, plays a more significant role than does acidosis in asphyxia-induced intestinal ischemia and pathology, and that hypoxic hypoxemia plays a more significant role than does ischemia or acidosis in asphyxia-induced decrease in ileal oxygen consumption.