HYPERBILIRUBINEMIA OF THE ELBW INFANTS

Hyperbilirubinemia
Most ELBW infants develop clinically significant typically unconjugated or indirect hyperbilirubinemia requiring treatment. Hyperbilirubinemia develops as a result of increased red blood cell turnover and destruction, an immature liver that is impaired during conjugation and elimination of bilirubin, and reduced bowel motility, which delays elimination of bilirubin-containing meconium. These manifestations of extreme prematurity in addition to typical conditions that cause jaundice (eg, ABO incompatibility, Rh disease, sepsis, inherited diseases) place these infants at higher risk for kernicterus at levels of bilirubin far below those in more mature infants. Kernicterus occurs when unconjugated bilirubin crosses the blood-brain barrier and stains the basal ganglia, pons, and cerebellum.

Infants with kernicterus who do not die may have sequelae such as deafness, mental retardation, and cerebral palsy. Phototherapy is used to decrease bilirubin levels to prevent the elevation of unconjugated bilirubin to levels that cause kernicterus.

Phototherapy, which uses special blue lamps with wavelengths of 420-475 nm, breaks down unconjugated bilirubin to a more water-soluble product via photoisomerization and photooxidation through the skin. Then, this product can be eliminated in bile and urine. The fluorescent bulbs are positioned at 50 cm above the infant with a resulting intensity of 6-12 μW/cm2. Tan has shown that the rate of bilirubin reduction is proportional to the light intensity. Phototherapy causes an increase in insensible water loss, so the amount of fluid intake typically should be increased. The infant's eyes are covered with patches to avoid exposure to blue light.

While phototherapy is initiated at birth of ELBW infants at some institutions, others start phototherapy when the bilirubin value approaches 50% of the birth weight value (eg, 4 mg/dL in an 800-g infant). If the level of bilirubin does not decrease satisfactorily with phototherapy, exchange transfusion is another option. If the level of bilirubin approaches 10 mg/dL (or 10 mg/dL/kg), exchange transfusion can begin to be considered in ELBW infants. In otherwise healthy term infants, exchange transfusion is not considered until the bilirubin level approaches 25 mg/dL.

In exchange transfusions, almost 90% of the infant's blood is replaced with donor blood, and the bilirubin level falls to 50-60% of the preexchange level. Complications include electrolyte abnormalities (hypocalcemia, hyperkalemia), acidosis, thrombosis, sepsis, and bleeding.