Phototherapy and Exchange Transfusion
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Direct answer
Phototherapy is the first-line treatment for neonatal hyperbilirubinaemia, using blue light in the 460 to 490 nanometre band to convert unconjugated bilirubin into excretable forms. Exchange transfusion is reserved for bilirubin levels that are dangerously high or do not respond to phototherapy, and it replaces the baby's blood to remove bilirubin and antibody. Decisions depend on total serum bilirubin, gestation, age in hours and risk factors.
What you must remember
- Mechanism: blue light photoisomerises unconjugated bilirubin into water-soluble isomers, notably lumirubin, which are excreted without conjugation.
- Wavelength: the 460 to 490 nanometre band, since bilirubin absorbs most strongly in the blue range.
- Dose: conventional phototherapy delivers an irradiance of roughly 8 to 12 microwatts per square centimetre per nanometre, while intensive phototherapy delivers 30 or more.
- Practice: the nappy stays on, the eyes are shielded, skin is exposed as widely as possible and feeds are frequent to support stool passage.
- Thresholds: total serum bilirubin is plotted against postnatal age in hours on gestation-specific curves, with lower thresholds for haemolysis, sepsis, asphyxia and prematurity.
- Exchange indications: bilirubin at or above the exchange threshold despite intensive phototherapy, signs of acute bilirubin encephalopathy, or rapid rise from haemolysis.
- Exchange volume: a double-volume exchange, about 160 millilitres per kilogram, given through an umbilical venous catheter with fresh, cross-matched, irradiated blood.
A stepwise double-volume exchange
Exchange transfusion is an invasive procedure, and examiners test both its sequence and its complications. The steps below describe the usual technique in a neonatal unit with a trained team.
- Preparation: Fresh, cross-matched, irradiated blood is prepared, and calcium, glucose and blood gases are checked before the procedure begins.
- Access: An umbilical venous catheter is placed, and the baby is monitored for heart rate, blood pressure and oxygen saturation throughout.
- Withdrawal and replacement: Small aliquots, typically 5 to 10 millilitres per kilogram, are withdrawn and replaced in alternating steps until about twice the estimated blood volume has been exchanged.
- Monitoring: Serum calcium, potassium, glucose and platelets are checked during and after the exchange, because citrate and the donor blood cause derangements.
- Complications: Hypocalcaemia, hyperkalaemia, arrhythmias, thrombocytopenia, necrotising enterocolitis, sepsis and portal vein thrombosis must each be watched for.
- Aftercare: Phototherapy usually continues and bilirubin is rechecked, since rebound hyperbilirubinaemia can occur while haemolysis persists.
The exchange is a bridge rather than a cure, and the baby's bilirubin is followed closely until the level is safely falling.
Where the exam tries to catch you
Phototherapy stems usually test the wavelength, the place of exchange in the sequence and the blood used for exchange.
- Trap: using exchange transfusion as first-line for any raised bilirubin. Correct: phototherapy is first-line, and exchange is reserved for levels at or above the exchange threshold or failure of phototherapy.
- Trap: choosing white light because it looks brighter. Correct: bilirubin absorbs most strongly in the blue band, so blue light in the 460 to 490 nanometre range is effective.
- Trap: using ordinary donor blood for exchange. Correct: fresh, cross-matched, irradiated blood is used to reduce the risk of graft-versus-host disease and other transfusion complications.
Frequently asked questions
What wavelength of light is used in neonatal phototherapy?
Neonatal phototherapy uses blue light in the 460 to 490 nanometre band, since bilirubin absorbs most strongly in this range. Light of this wavelength converts unconjugated bilirubin in the skin into forms that the baby can excrete.
What volume is used in an exchange transfusion for neonates?
An exchange transfusion for neonates is usually a double-volume exchange, about 160 millilitres per kilogram, which replaces roughly twice the estimated blood volume. It is performed through an umbilical venous catheter using fresh, cross-matched, irradiated blood.
What are the complications of exchange transfusion in neonates?
Complications of exchange transfusion in neonates include hypocalcaemia, hyperkalaemia, arrhythmias, thrombocytopenia, necrotising enterocolitis, sepsis and portal vein thrombosis. Calcium, potassium and platelets are monitored during and after the procedure.
How is the need for phototherapy decided in neonatal jaundice?
The need for phototherapy is decided by plotting total serum bilirubin against postnatal age in hours on gestation-specific curves, with lower thresholds for risk factors. Local guidance, such as current IAP recommendations, should be checked for the exact threshold in use.