What it is
Symptomatic neonatal polycythemia (hyperviscosity) is treated with a partial exchange transfusion (PET): whole blood is removed in aliquots and replaced isovolumetrically with crystalloid, lowering the haematocrit while preserving circulating volume. This calculator returns the volume of whole blood to remove (equal to the volume of normal saline to replace) to reach a target Hct.
The formula
$$ Volume\ (mL) = \frac{EBV \times (Hct_{initial} - Hct_{goal})}{Hct_{initial}} $$
where EBV = estimated blood volume = weight (kg) × the per-kg estimate. Doctaverse uses 85 mL/kg for term and 100 mL/kg for preterm infants. The goal Hct must be below the initial Hct (the tool rejects an equal or higher goal), and the typical target is 50–55%.
When to use it
- Symptomatic polycythemia with venous Hct >65% (lethargy, jitteriness, poor feeding, hypoglycaemia, respiratory or perfusion signs).
- Asymptomatic infants with venous Hct >75% by many unit protocols.
- Confirm on a venous (not capillary or warmed-heel) sample first — capillary haematocrits run falsely high.
Worked example
A term, 3000 g infant with an initial Hct of 70%, targeting 55%:
- EBV = 85 mL/kg × 3.0 kg = 255 mL
- Volume = 255 × (70 − 55) / 70 = 255 × 15 / 70 ≈ 55 mL
Remove ~55 mL of whole blood in aliquots, replacing each with an equal volume of normal saline, then recheck the Hct.
Pitfalls
- Crystalloid, not blood. Replacement is with normal saline (or another isotonic crystalloid), not donor blood — using albumin or plasma adds cost and infection risk without benefit.
- Verify the haematocrit source. Acting on a falsely high capillary Hct leads to unnecessary, invasive intervention. Use a free-flowing venous sample.
- EBV assumption matters. The volume scales directly with the per-kg estimate; pick the gestation band correctly (preterm 100 vs term 85 mL/kg). Some guidelines use ~90 mL/kg uniformly — know your unit’s convention.
- Marginal benefit. Cochrane evidence shows PET reduces short-term respiratory and neurological signs but has not been shown to improve long-term neurodevelopment, and it carries a possible NEC signal — reserve it for genuinely symptomatic infants and recheck the Hct after the procedure.
- Re-equilibration can raise the Hct again over hours; monitor and recheck.
Run it: Partial Exchange Transfusion (Polycythemia)
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.