Perfusion Pro Logo

Perfi

Coffee

Hemodilution Calculator

Estimate final hematocrit and calculate required blood volume.

Input Parameters

Enter patient, prime, and target data.

Clinical Context & Significance

Hemodilution is a deliberate practice in cardiopulmonary bypass (CPB) where the patient's blood is diluted with the non-hemic priming volume of the extracorporeal circuit. This process results in a decrease in hematocrit and hemoglobin concentration, which has both physiological advantages and risks.

Physiological Benefits

  • Decreased blood viscosity, improving microcirculatory flow.
  • Reduced peripheral resistance, aiding tissue perfusion.
  • Decreased risk of thromboembolic complications.
  • Improved flow during hypothermia as viscosity naturally increases with cold.

Critical Thresholds

While hemodilution is beneficial, extreme dilution can impair oxygen-carrying capacity. Most clinical protocols target a hematocrit of 21-25% during normothermic bypass, although higher levels may be required for specific patient populations or deep hypothermic cases.

Reference: Gravlee's Cardiopulmonary Bypass: Principles and Practice. The formula used here follows the standard mass balance equation: (C1 * V1) + (C2 * V2) = C3 * V3.

Clinical Perfusion Practice of Acute Normovolemic Hemodilution & Hematocrit Management

Physiological Principles & Clinical Context

The initiation of CPB requires filling the extracorporeal circuit (tubing, reservoir, oxygenator) with a crystalloid or colloid prime (typically 1200–1500 mL for adults). This priming volume causes acute normovolemic hemodilution, reducing the patient's circulating hematocrit (HCT) and blood viscosity. While hemodilution improves microcirculatory flow, reduces shear stress, and prevents thrombotic complications during hypothermic bypass, excessively low hematocrit (HCT < 20% to 22%) limits arterial oxygen-carrying capacity, potentially leading to tissue hypoxia, anaerobic metabolism, and cardiac surgery-associated acute kidney injury (CSA-AKI). Monitoring and predicting post-prime HCT allows the perfusionist to plan for blood additions or ultrafiltration.

Clinical Targets & Safe Ranges

  • •Target On-Bypass Hematocrit: 21% to 25% for low-risk adult patients.
  • •High-Risk / Vulnerable Patients: 24% to 28% for elderly, diabetic, renal, or severe ventriculopathic patients.
  • •Transfusion Trigger Threshold: Standardly considered when hematocrit drops below 20% to 21% on bypass.
  • •Ultrafiltration (MUF/CUF): Indicated during or post-bypass when fluid removal is required to concentrate hematocrit without blood cell transfusion.

Mathematical Formulation

  • ƒEstimated Blood Volume (EBV) - Adult Male: EBV (mL) = Weight (kg) × 75 mL/kg
  • ƒEstimated Blood Volume (EBV) - Adult Female: EBV (mL) = Weight (kg) × 65 mL/kg
  • ƒPost-Prime Hematocrit: Hct (%) = [ (EBV × Patient Hct) + (Prime Vol × Prime Hct) ] / (EBV + Prime Vol)
  • ƒRequired Blood Product Volume: Blood Vol (mL) = Total Vol × (Target Hct - Current Hct) / (Blood Product Hct - Target Hct)

Academic & Clinical References

  1. Shann KG, Likosky DS, Murkin JM, et al. An American Society of ExtraCorporeal Technology (AmSECT) clinical practice guideline: inflammatory response, microemboli, and hemodilution. J Extra Corpor Technol. 2015;47(1):15-28.
  2. Ranucci M, Romitti F, Isgrò G, et al. Oxygen delivery, hematocrit, and acute kidney injury during cardiopulmonary bypass. Ann Thorac Surg. 2005;80(6):2182-2189.