Estimated Blood Volume and Allowable Blood Loss
Blood volume from weight and age group, and how much blood can be lost before reaching a chosen hematocrit. The result updates as you type.
Method
EBV = weight × blood volume per kg
MABL = EBV × (Hctstart − Hctlowest) ÷ Hctaverage
The maximum allowable blood loss (MABL) uses the Gross formula, which divides by the average of the starting and lowest hematocrit to account for ongoing hemodilution as blood is lost and replaced with crystalloid or colloid.
Blood volume per kilogram falls with age, from about 90–100 mL/kg in preterm neonates to 65–75 mL/kg in older children and adults. The ranges shown are typical of pediatric anesthesia references and vary between sources.
Cranial vault surgery in infants can involve blood loss approaching or exceeding one blood volume. This estimate is a planning aid. Transfusion decisions depend on ongoing losses, hemodynamics, and laboratory values.
Source: Gross JB. Estimating allowable blood loss: corrected for dilution. Anesthesiology. 1983;58(3):277–280. Find on PubMed.