Organ blood flow redistribution in response to hypoxemia in neonatal piglets

This study was designed to determine the effects of severe hypoxemia on new born piglet visceral blood flow. While the hemodynamic effects of a severe hypoxemic insult are well characterized in newborn animals, its impact on o rgan perfusion in premature infants is not well characterized. Cannulas wer e placed in the femoral vessels and left atrium of term (1-14 days old) and prematurely delivered (cesarean section at 90% of term gestation) piglets. After stabilization, some animals were subjected to 1 h of ventilator-cont rolled hypoxia (yielding PaO2 approximate to 30-40 torr) followed by 30 min of reoxygenation; the remaining animals served as unchallenged controls. R adiolabeled microspheres were injected in all animals at times 0 min (basel ine), 5 and 60 min (hypoxia), and 90 min (reoxygenation). Blood flows (mL/m in/g tissue) to organs were determined using reference organ techniques. Co ntrol animals displayed no alterations in any of the variables monitored. T hroughout the experimental period, organ blood flows were almost uniformly lower (p < .05, ANOVA) in premature versus term animals. The trend toward i ncreased cerebral and cardiac blood flows during hypoxia observed in the pr emature piglets was similar to that of term animals, but of lower magnitude . In term piglets, hypoxia produced an immediate and significant (*p < .05) decline in small-intestinal blood flow followed by autoregulatory escape ( 2.02 +/- 0.17 mL/min/g at time 0, 1.56 +/- 0.15 mL/min/g at 5 min hypoxia, 1.88 +/- 0.18 mL/min/g at 60 min hypoxia, 2.26 +/- 0.19 mL/min/g at 30 min reoxygenation), an effect not readily observed in the premature piglets (0. 48 +/- 0.10 mL/min/g at time 0, 0.44 +/- 0.07 mL/min/g at 5 min hypoxia, 0. 46 +/- 0.10 mL/min/g at 60 min hypoxia, 0.42 +/0 0.08 mL/min/g at 30 min re oxygenation). However, mucosal blood flows measured in these younger animal s declined throughout the experimental period to almost 50% of baseline, co mpared to a complete restoration to baseline blood flow observed following reoxygenation of term piglets. Intestinal blood flow in premature infants i s small when compared to term animals, and alterations in small intestinal blood mucosalflow induced by hypoxia appear less well tolerated by the prem ature animals. Taken together, this may in part account for the increased r isk of developing intestinal ischemic diseases in premature infants who are even temporarily exposed to a severe hypoxic challenge.