How is estimated total blood volume computed?

Calculation of Estimated Total Blood Volume

Estimated total blood volume (EBV) is most commonly calculated using a standard formula of 70 mL/kg of body weight, though this should be adjusted based on gender, age, and body composition for more accurate results. 1, 2

Standard Calculation Methods

• The traditional formula for calculating estimated blood volume is:

  • EBV = 70 mL/kg × body weight 1, 2
  • This is the standard value used for adults of normal weight 2

• For gender-specific calculations:

  • Males: 75 mL/kg × ideal body weight 3
  • Females: 65 mL/kg × ideal body weight 3

• For age-specific calculations:

  • <65 years: 70 mL/kg × ideal body weight 3
  • ≥65 years: 60 mL/kg × ideal body weight 3

Advanced Calculation Methods

• For acute normovolemic hemodilution (ANH), a more precise formula is used:

  • V = EBV × (Ho − Hf / Hav) 1
  • Where:
    • V = volume to be removed
    • EBV = estimated blood volume (70 mL/kg body weight)
    • Ho = initial hematocrit
    • Hf = desired hematocrit
    • Hav = average hematocrit (mean of Ho and Hf) 1

• For pediatric patients, blood volume varies by weight:

  • ≤1 kg: 4% of total blood volume (approximately 50-99 mL total) 1
  • 1.1-2 kg: 4% of total blood volume (approximately 100-200 mL total) 1
  • 2.1-12.7 kg: 3% of total blood volume (>200 mL total) 1
  • 12.8-36.3 kg: 2.5% of total blood volume (>800 mL total) 1

  • 36.3 kg: 1.8-2.7% of total blood volume (>2200 mL total) 1

Limitations and Adjustments

• Standard formulas become less accurate in obese and morbidly obese patients as indexed blood volume decreases in a non-linear manner with increasing weight 4

• More accurate estimations require adjustments using ideal body weight rather than actual body weight 3, 5

• Hematocrit affects total blood volume - two individuals with the same body size and gender can have different total blood volumes depending on their hematocrit 5

• Allen's formula and Nadler's formula provide more accurate estimations than simple weight-based calculations, especially when modified to account for hematocrit 5

Clinical Applications

• For therapeutic phlebotomy, the standard volume removed is 500 mL per session in adults 2

• For patients undergoing cardiac surgery with cardiopulmonary bypass, accurate blood volume estimation is crucial for predicting dilutional hematocrit and oxygen delivery 3, 5

• In patients with cardiac disease, extra caution is needed during phlebotomy procedures, with normovolemia maintained by matching volume replacement with blood removal 2, 1

• For pediatric blood sampling, recommended volumes are based on weight and total blood volume to avoid excessive blood draw 1

Understanding the patient's estimated blood volume is essential for procedures involving blood removal or transfusion, with more accurate calculations requiring consideration of multiple factors beyond simple weight-based formulas.