Physiologic Mechanisms of Neonatal Jaundice
At any time in the infant’s first few days after birth, the serum bilirubin level reflects a combination of the effects of bilirubin production, conjugation, and enterohepatic circulation. Using measurements of blood carboxyhemoglobin (COHb) corrected for ambient CO (COHbc) as an index of bilirubin production and high-performance liquid chromatography (HPLC) measurements of conjugated bilirubin, Kaplan and associates (25) demonstrated that an imbalance between bilirubin production and conjugation is fundamental in the pathogenesis of neonatal bilirubinemia. Several processes account for the bilirubinemia that occurs in virtually all newborns (Table 35-3).
Increased Bilirubin Load on the Liver Cell
Bilirubin Production
CO is produced in equimolar quantities with bilirubin and measurements of CO production show that the normal
newborn produces an average of 8 to 10 mg/kg (13.7 to 17.1 μmol/ kg) of bilirubin per day (26,27). This is more than twice the rate of normal daily bilirubin production in the adult and is explained by the fact that the neonate has a higher circulating erythrocyte volume, a shorter mean erythrocyte lifespan, and a larger early labeled bilirubin peak (see Table 35-3). Bilirubin production decreases with increasing postnatal age but is still about twice the adult rate by age 2 weeks (26).
newborn produces an average of 8 to 10 mg/kg (13.7 to 17.1 μmol/ kg) of bilirubin per day (26,27). This is more than twice the rate of normal daily bilirubin production in the adult and is explained by the fact that the neonate has a higher circulating erythrocyte volume, a shorter mean erythrocyte lifespan, and a larger early labeled bilirubin peak (see Table 35-3). Bilirubin production decreases with increasing postnatal age but is still about twice the adult rate by age 2 weeks (26).
TABLE 35-3 PHYSIOLOGIC MECHANISMS OF NEONATAL JAUNDICE | ||||
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