Our blood volume calculator uses three methods to determine the total blood volume. The first one uses Dr. Nadler's formula, the second one is an equation developed by Dr. Lemmens, Dr. Bernstein, and Dr. Brodsky, and in `advanced mode`

you can find a very simple method that gives a better perspective on the previous two.

Preoperative assessment of estimated blood volume (BV) is essential for patients undergoing surgery. It impacts perfusion care, including hemodynamic and pharmacologic interventions, and transfusion practices. Keep on reading to understand how blood volume affects blood pressure.

Please note that this is a calculator of blood volume for adults. If you want to estimate the blood volume in a child, use our pediatric blood volume calculator.

## How does blood volume calculator work?

There are several methods available to directly or indirectly measure blood volume, but all are impractical in routine clinical practice. The mean value for indexed blood volume (ᵢBV) in normal weight adults is `70 mL/kg`

for males and `65 mL/kg`

for females. You can find the option to calculate it this way in `advanced mode`

. Since ᵢBV decreases in a non-linear manner with increasing weight, this value can't be used for obese and morbidly obese patients. The methods of estimating total blood volume we provide here take into account the entire range of body weights.

## Nadler's Equation for total blood volume - Method 1

An advanced formula used to calculate blood volume was developed by Dr. Allen in 1956. In 1962, basing on Dr. Allen's work, Dr. Nadler found more accurate coefficients and published the equation in his article titled *Prediction of blood volume in normal human adults*.
Our Blood Volume calculator uses this formula:

**For males**:

`BV = 0.3669 * h³ + 0.03219 * w + 0.6041`

**For females**:

`BV = 0.3561 * h³ + 0.03308 * w + 0.1833`

## Lemmens-Bernstein-Brodsky Equation for estimated blood volume - Method 2

In 2006, Dr. Lemmens, Dr. Bernstein, and Dr. Brodsky discovered an equation that allows physicians to predict ᵢBV over the full spectrum of body weights and body mass indices (BMI) in patients unstressed by acute trauma or critical illness. The blood volume calculator uses this formula:

`BV = 70 / √(BMI / 22)`

## How does blood volume affect blood pressure?

Factors that affect blood pressure (BP) are interconnected:

- peripheral resistance - the constriction of the arteries elevates the BP. Peripheral resistance also includes: vessel length, blood viscosity, and arterial stenosis;
- total blood volume;
- cardiac output.

The dynamic balance between blood volume and blood pressure is regulated by the complex Renin-Angiotensin-Aldosterone system (RAAS) controlled by the kidneys. In normal conditions, it maintains the blood pressure in the range of 90-140 mmHg (systolic BP) and 60-90 mmHg (diastolic BP).