BODY FLUIDS AND BLOOD LOSS

The total volume of body fluids represents 60% of lean body weight (or 600 mL/kg) in men and 50% of lean body weight (or 500 mL/kg) in women. The volume of whole blood is 6.0 to 6.6% of lean body weight (or 60 to 66 mL/kg), which means that only 11 (i.e., 66/600) to 12% (60/500) of the total body fluid volume is in the intravascular compartment. Approximately 60% of the blood volume is in the plasma fraction, and the remaining 40% represents the erythrocyte volume. The corresponding volumes for an average-size adult man (weighing 80 kg or 176 lbs) and adult woman (weighing 60 kg or 132 lbs) is shown below.

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80-kg Man 60-kg Woman

Total body fluids 48 L 30 L

Whole blood 5.3 L 3.6 L

Plasma 3.2 L 2.2 L

Erythrocytes 2.1 L 1.4 L

Adjustments

The American Association of Blood Banks recommends the following adjustments for estimating blood, plasma, and erythrocyte volumes based on body weight .

1. For obese and elderly patients, estimate the volumes based on lean body weight and reduce the values by 10%.

2. For patients with a marked weight loss within 6 months, use the premorbid weight loss to estimate volumes.