How to Calculate Estimated Blood Loss
What is Estimated Blood Loss?
Estimated blood loss (EBL) during surgery uses pre- and post-operative haematocrit values with the Gross formula to quantify blood lost.
Formula
Estimated blood loss (mL) = Hemoglobin change (g/dL) × Weight (kg) × Estimated blood volume (70 mL/kg) / Pre-operative Hgb
- PreHgb
- Pre-operative hemoglobin (g/dL)
- PostHgb
- Post-operative hemoglobin (g/dL)
- Weight
- Body weight (kg)
- BloodLoss
- Estimated blood loss (mL)
Step-by-Step Guide
- 1EBL = EBV × (HCT_pre − HCT_post) / HCT_avg
- 2EBV ≈ 70 mL/kg (average adult)
- 3HCT as decimals (40% → 0.40)
- 4Clinical estimate only — always correlate with signs
Worked Examples
Input
80 kg, HCT pre 0.42, post 0.30
Result
EBL = 5600 × 0.12/0.36 ≈ 1,867 mL
Frequently Asked Questions
Why is estimated blood loss important?
Helps surgeons/anesthesiologists assess adequate fluid replacement, need for transfusion, ongoing bleeding risk. Underestimating = inadequate resuscitation; overestimating = unnecessary transfusions.
Is hemoglobin drop a reliable estimate?
Decent proxy. But affected by fluid administered, ongoing losses. Direct measurement (weighing gauze, cell salvage) more accurate. Hemoglobin drop estimates minimum loss.
What about ongoing oozing?
Persistent low-grade bleeding can add up. Monitor hourly drain output post-op. > 200 mL/hr suggests coagulopathy or inadequate hemostasis. Intervention needed.
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