What it is
Estimated blood volume (EBV) is the calculated circulating blood volume of a patient, derived from body weight and an age-specific per-kilogram constant. It is the foundational number behind several point-of-care calculations: transfusion volumes, exchange-transfusion and partial-exchange math, and maximum allowable blood loss (MABL) during surgery. Neonates carry proportionally more blood per kilogram than older children and adults, so the constant falls as the patient ages.
The formula
EBV (mL) = weight (kg) × blood volume per kg (mL/kg)
The per-kg constant by age band:
| Age band | mL/kg |
|---|---|
| Preterm neonate | 95 |
| Term neonate | 85 |
| Infant (1–12 mo) | 80 |
| Child (1–12 yr) | 75 |
| Adolescent / adult | 70 |
When to use it
Reach for EBV whenever you need to scale a volume to a child’s circulation:
- Calculating a packed-red-cell transfusion (commonly 10–15 mL/kg PRBC).
- Setting up an exchange or partial-exchange transfusion (e.g. polycythemia, severe hyperbilirubinemia).
- Feeding the MABL formula before a procedure with anticipated blood loss.
- Estimating the clinical significance of a measured blood loss as a percentage of circulating volume.
Worked example
A 6-month-old infant weighs 8 kg. The infant band is 80 mL/kg.
EBV = 80 × 8 = 640 mL
That 640 mL is the denominator you would carry into a transfusion or MABL calculation. For contrast, a 3 kg term neonate (85 mL/kg) has an EBV of just 255 mL — a reminder of how little absolute blood loss is tolerated at this size.
Pitfalls
- Pick the right band. A premature neonate uses 95 mL/kg, not 85 — getting the band wrong skews every downstream calculation.
- Use actual weight, not ideal or estimated, when known. In emergencies an estimated weight (APLS/Broselow) is acceptable, but flag the uncertainty.
- EBV is an estimate, not a measurement. Obesity, dehydration, and chronic anemia all shift true circulating volume. Treat the number as a planning figure, then titrate to the patient.
- Don’t confuse plasma volume with whole-blood volume when calculating exchange or apheresis targets.
Run it: Estimated Blood Volume (EBV): Age-Band mL/kg Values for Pediatrics
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.