How is oxygen delivery (DO2) calculated?

Oxygen delivery is arterial oxygen content multiplied by cardiac output. Arterial content (CaO2) equals 1.34 times haemoglobin times arterial saturation, plus 0.0031 times PaO2. DO2 in mL/min equals CaO2 times cardiac output in L/min times 10 to reconcile the units.

What is the oxygen extraction ratio?

The oxygen extraction ratio (O2ER) is the fraction of delivered oxygen that the tissues consume, calculated as VO2 divided by DO2, or equivalently (CaO2 minus CvO2) divided by CaO2. A normal value is around 0.20 to 0.30; a rising ratio signals that delivery is struggling to meet demand.

Why is the dissolved oxygen term included?

Most oxygen is carried bound to haemoglobin, but a small amount is dissolved in plasma, equal to 0.0031 mL per dL per mmHg of PaO2. At normal pressures this is tiny, but it becomes meaningful at high inspired oxygen or in severe anaemia, so it is included for accuracy.

What are normal DO2 and VO2 values?

In a typical adult, oxygen delivery is roughly 950 to 1150 mL/min, the DO2 index 500 to 600 mL/min/m2, oxygen consumption around 200 to 250 mL/min, and the extraction ratio 0.20 to 0.30. These vary with body size, temperature, sedation and metabolic state.

What does a low mixed venous saturation tell me?

A falling mixed venous oxygen saturation (SvO2), typically below about 65 percent, means tissues are extracting more oxygen because delivery is inadequate relative to demand. Causes include low cardiac output, anaemia, hypoxaemia or increased consumption such as fever or shivering.

Oxygen Delivery (DO₂) & Consumption (VO₂) Calculator

Oxygen transport at the bedside

Oxygen delivery and consumption are central to managing shock, sepsis and critical illness — they describe whether enough oxygen is reaching the tissues and how hard the body is working to extract it. This calculator derives DO₂, VO₂, arterial and venous oxygen content and the extraction ratio from haemoglobin, saturations and cardiac output.

How it works

The chain starts with oxygen content of arterial and venous blood, using Hüfner’s constant (1.34 mL O₂ per gram of haemoglobin) plus the small dissolved term:

CaO2 = (1.34 × Hb × SaO2) + (0.0031 × PaO2)
CvO2 = (1.34 × Hb × SvO2) + (0.0031 × PvO2)

From there:

DO2  = CaO2 × CO × 10            (mL/min)
VO2  = CO × (CaO2 − CvO2) × 10   (Fick principle)
O2ER = (CaO2 − CvO2) / CaO2

The factor of 10 converts content in mL/dL and flow in L/min into mL/min. Supplying body surface area gives the indexed DO₂ and VO₂.

Notes and example

For Hb 14 g/dL, SaO₂ 98%, SvO₂ 70% and a cardiac output of 5 L/min, arterial content is about 18.7 mL/dL, giving a DO₂ near 935 mL/min and an extraction ratio around 0.28 — squarely normal.

Watch trends rather than single numbers. A rising extraction ratio or falling SvO₂ is an early warning that delivery is no longer keeping pace with demand, often before blood pressure changes. Treat the dissolved-oxygen term as minor at normal pressures but real in severe anaemia or high-FiO₂ states.