Predicted Hematocrit Calculator for CPB Perfusion
Estimate dilutional hematocrit on bypass from EBV, prime, added fluids, ultrafiltration, and RBC products before or during CPB.
Predicted Hct on CPB
Dilutional hematocrit calculator
Estimate dilutional hematocrit at CPB initiation.
Predicted post-adjustment result
Current Hct: 0.0% → Predicted Hct: 0.0%
Change: 0.0 percentage points
Clinical context
• Target ranges: Many adult programs maintain approximately 21–30% on pump, with higher goals in pediatric and neonatal patients.
• Practical levers: Lower prime volume and UF tend to raise Hct, while crystalloid additions lower Hct.
• Transfusion planning: RBC unit count, unit volume, and unit Hct assumptions directly shift predicted output.
• On-pump hematocrit adjustment: On-pump adjustment uses a simplified CPB volume estimate based on estimated blood volume plus priming volume. It applies the current measured Hct to that volume, then estimates the effect of planned crystalloid addition, RBC transfusion, or ultrafiltration.
• RBC note: RBC transfusion increases both red cell volume and total circulating volume. During CPB, the Hct rise from 1 unit may be smaller than expected when the estimated CPB volume is large.
Educational support tool only; verify with measured laboratory values.
This is a simplified mixing estimate. Actual Hct may differ due to reservoir level changes, sampling timing, ongoing bleeding, cell saver return, cardioplegia return, ultrafiltration efficiency, and institutional practice.
Practical notes
• A lower predicted Hct may be acceptable during hypothermic CPB when metabolic demand is reduced, but adequacy should still be assessed with oxygen delivery and clinical markers.
• A normal predicted Hct does not guarantee adequate oxygen delivery if pump flow, arterial saturation, hemoglobin concentration, or microcirculatory conditions are unfavorable.
• The calculator estimates hematocrit change from volume balance. It does not replace transfusion thresholds, institutional blood conservation protocols, or patient-specific clinical judgment.
• When the predicted Hct is near a local transfusion threshold, consider confirming with measured Hct after adequate mixing time.
▶ Methodology & limitations
EBV model: Estimated blood volume, EBV (mL), is calculated from body weight and the selected EBV coefficient.
EBV = Weight (kg) × EBV coefficient (mL/kg).
Red cell volume: Patient red cell volume is estimated from EBV and pre-CPB hematocrit.
RBC_patient = EBV × (Pre-CPB Hct ÷ 100).
Red cell volume added from transfusion is estimated from RBC unit volume and unit hematocrit.
RBC_products = RBC units × RBC volume per unit × (Unit Hct ÷ 100).
Total circulating volume: Total volume includes estimated blood volume, CPB prime volume, and RBC product volume.
V_total = EBV + Prime volume + RBC product volume.
Predicted hematocrit: Predicted Hct is calculated as total red cell volume divided by total circulating volume.
Predicted Hct (%) = [(RBC_patient + RBC_products) ÷ V_total] × 100.
On-pump adjustment model:
Estimated CPB volume = EBV + Prime volume.
Current RBC volume = Estimated CPB volume × (Current Hct ÷ 100).
Added RBC volume = RBC units × RBC volume per unit × (Unit Hct ÷ 100).
Final estimated volume = Estimated CPB volume + Fluid added + RBC product volume − UF removed.
Predicted post-adjustment Hct (%) = [(Current RBC volume + Added RBC volume) ÷ Final estimated volume] × 100.
If manual current volume override is active, the manual value replaces EBV + Prime volume as the estimated CPB volume.
Limitations: This is a simplified complete-mixing model. Actual hematocrit may differ because of reservoir level changes, sampling timing, ongoing bleeding, cell saver return, cardioplegia return, hemolysis, sequestration, rapid volume shifts, ultrafiltration efficiency, and uncertainty in patient-circuit volume. Use with clinical markers and local protocol.