The effects of brain blood flow on brain bilirubin deposition in newborn piglets.

Since kernicteric lesions are usually found in the subcortical regions of the brain and these areas also receive the highest blood flow during asphyxia and hypercapnia, we hypothesized that increases in brain bilirubin deposition may be related to increases in brain blood flow. Fourteen piglets underwent a 3-h infusion of bilirubin to maintain total serum bilirubin at approximately 8 mg/dl, during which time blood gases, hemodynamic variables, and brain blood flow were determined. After sacrificing the animals, regional brain bilirubin content was determined. Ten piglets underwent the same protocol; in addition, hypercapnia was induced during the last hour of study (PaCO2 approximately 70 mm Hg). The regional brain blood flow and bilirubin deposition were significantly increased over control values (p less than 0.05) following hypercapnia in the subcortical region and significantly so in the midbrain and cerebellum. In separate groups of control (n = 6) and hypercapnia (n = 6) piglets, 125I-labeled albumin was infused and demonstrated that hypercapnia was not associated with increased regional brain albumin content. We conclude that hypercapnia-induced augmentation in regional brain blood flow is associated with increased deposition brain blood flow is associated with increased deposition of unbound bilirubin. Although the causal relationship between these two observations has not been firmly established, the findings deserve future investigation to clarify the role of brain blood flow, brain bilirubin deposition, and the production of kernicterus in high risk infants.