Neonatal Hyperbilirubinemia - Exam Notes

Q1. Causes and Management of Unconjugated Neonatal Hyperbilirubinemia (5 Marks - SMIMER)

Definition

CAUSES

A. Physiologic (Most Common)

• Physiologic jaundice of the newborn: Immature neonatal liver cannot adequately conjugate bilirubin (glucuronyl transferase deficiency). Bilirubin typically peaks at ~5 mg/dL on day 3 of life and resolves by 2 weeks. Occurs in ~50% of normal newborns.

B. Increased Bilirubin Production (Hemolysis)

C. Decreased Hepatic Uptake/Conjugation

• Prematurity (underdeveloped conjugation enzymes)
• Drugs (competitive inhibition)
• Gilbert syndrome (reduced UGT1A1 activity)
• Crigler-Najjar syndrome (types I and II - absent/severely reduced UGT1A1)
• Congenital hypothyroidism
• Galactosemia
• Sepsis, fasting

D. Increased Enterohepatic Circulation

• Breast milk jaundice: hormonally mediated or increased enterohepatic reabsorption; peaks at 10-21 days, may persist 3-10 weeks
• Intestinal obstruction (meconium ileus, Hirschsprung disease, pyloric stenosis, duodenal atresia)

E. Miscellaneous

• Dehydration
• Polycythemia (rapid turnover of increased RBC mass)

MANAGEMENT

1. Assessment / Monitoring

• Total serum bilirubin (TSB) plotted on hour-specific nomogram (Bhutani curve) per AAP 2004 guidelines
• Transcutaneous bilirubin for screening
• Evaluate for pathologic causes if: jaundice within 24 hr of birth, rising TSB unresponsive to phototherapy, jaundice persisting >3 weeks, or direct bilirubin elevated

2. Supportive Measures

• Adequate feeding (reduces enterohepatic circulation)
• Treat underlying cause (e.g., antibiotics for sepsis, thyroid hormone for hypothyroidism)

3. Phototherapy

• First-line treatment for elevated unconjugated bilirubin
• Blue-green light (460-490 nm) converts unconjugated bilirubin to water-soluble photoisomers (lumirubin) excreted in urine and bile without conjugation
• Can be delivered via overhead halogen/LED banks or fiberoptic "bili-blanket"
• Initiated at TSB thresholds based on gestational age and risk factors

4. Exchange Transfusion

• For TSB >25 mg/dL or rising rapidly despite phototherapy, or signs of acute bilirubin encephalopathy
• Reduces TSB by ~25% per double-volume exchange

5. IVIG

• 0.5-1 g/kg for isoimmune hemolysis (Rh/ABO) if TSB approaching exchange threshold - though recent evidence questions its benefit and it may increase risk of necrotizing enterocolitis

Q2. Exchange Transfusion in Neonatal Hyperbilirubinemia - Role and Indications (5 Marks - NAMO)

Role / Rationale

1. Removing circulating unconjugated bilirubin from the plasma
2. Removing sensitized/hemolysing red cells (in Rh/ABO incompatibility)
3. Removing circulating maternal antibodies responsible for ongoing hemolysis
4. Correcting anemia and restoring normal RBC mass
5. Preventing kernicterus (bilirubin deposition in basal ganglia, cerebellum, brainstem nuclei)

• Reduces total bilirubin by approximately 25%
• Reduces fetal (sensitized) red cell mass by approximately 70%

INDICATIONS

Absolute Indications

1. Total serum bilirubin (TSB) >25 mg/dL in a term neonate (not responding to phototherapy)
2. TSB reaching exchange threshold based on the AAP hour-specific nomogram (TSB plotted against postnatal age in hours, accounting for risk factors)
3. Signs of acute bilirubin encephalopathy (ABE) regardless of bilirubin level: somnolence, poor feeding, hypertonia/hypotonia, high-pitched cry, opisthotonos, retrocollis, seizures
4. Rapid rate of rise of TSB (>0.5 mg/dL/hr) despite intensive phototherapy
5. TSB rising to within 2-3 mg/dL of exchange threshold despite intensive phototherapy in isoimmune hemolysis (Rh/ABO disease)
6. Erythroblastosis fetalis with severe hemolysis and anemia

Relative Indications

• Hemolytic disease of the newborn (HDN) with rising TSB not controlled by phototherapy
• Preterm infants at lower TSB thresholds (more vulnerable blood-brain barrier)
• Infants with hypoxia, acidosis, hypoalbuminemia (increases free unconjugated bilirubin)

Complications of Exchange Transfusion

• Mortality: ~3 per 1000 in term infants; up to 10% in preterm infants
• Morbidity in up to 25% of procedures:
  • Catheter-related complications (portal vein thrombosis, air embolism)
  • Infection/sepsis
  • Cardiorespiratory instability (arrhythmias, bradycardia)
  • Hypocalcemia, hypoglycemia, hyperkalemia (from citrated blood)
  • Necrotizing enterocolitis (NEC)
  • GVHD (if blood not irradiated)

Given these risks, the incidence of ET has declined significantly due to early implementation of intensive phototherapy.

Q3. Phototherapy - Mechanism and Complications (5 Marks - KMCRI)

Mechanism of Phototherapy

1. Photoisomerization (Main Mechanism - ~80%)

• Native unconjugated bilirubin (4Z,15Z-bilirubin) is converted to configurational isomers (e.g., 4Z,15E-bilirubin / lumirubin)
• These isomers are water-soluble and can be excreted directly into bile without hepatic conjugation
• This is the primary and most clinically significant mechanism

2. Structural Isomerization (Lumirubin formation)

• A more stable and polar isomer called lumirubin is produced irreversibly
• Lumirubin can be excreted in both urine and bile
• Although it forms slowly, it is rapidly excreted and does not undergo back-isomerization

3. Photooxidation (Minor, slow mechanism)

• Bilirubin is oxidized to colorless polar products (di-pyrroles)
• These are excreted in urine
• Relatively slow and less important clinically

Complications of Phototherapy