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.

Why clinicians use indexed values

Raw DO₂ and VO₂ depend on body size: a large patient will have higher absolute values than a small one even at equivalent physiology. Dividing by body surface area (BSA) gives the DO₂ index (DO₂I) and VO₂ index (VO₂I), which allow comparison across patients of different sizes and are more useful for trending during resuscitation and for referencing against published normal ranges.

What each output tells you clinically

CaO₂ (arterial oxygen content) reflects how much oxygen each decilitre of blood carries away from the lungs. It is almost entirely determined by haemoglobin and arterial saturation — a low CaO₂ points to anaemia or hypoxaemia as the primary deficit rather than a cardiac problem.

DO₂ (oxygen delivery) is the product of CaO₂ and cardiac output. When it falls, the body compensates by extracting a higher fraction of delivered oxygen, which shows up as a rising extraction ratio and falling SvO₂. Identifying whether the deficit is from haemoglobin, saturation, or cardiac output guides whether to give blood, increase FiO₂, or target cardiac output.

VO₂ (oxygen consumption, Fick method) is the true tissue oxygen uptake. In sepsis or fever, VO₂ rises because metabolic demand increases. In cardiogenic shock, delivery falls but demand stays the same, driving a widened arteriovenous oxygen difference.

O₂ER (oxygen extraction ratio) of around 0.20 to 0.30 is normal. Values rising toward 0.50 to 0.60 indicate the tissues are compensating maximally for low delivery — a physiological warning that supply is becoming inadequate. Beyond that ceiling, VO₂ becomes delivery-dependent and anaerobic metabolism begins.

Worked example

Inputs: Hb 9 g/dL, SaO₂ 98%, PaO₂ 90 mmHg, SvO₂ 58%, PvO₂ 28 mmHg, cardiac output 3.8 L/min.

CaO2 = (1.34 × 9 × 0.98) + (0.0031 × 90) = 11.82 + 0.28 = 12.10 mL/dL
CvO2 = (1.34 × 9 × 0.58) + (0.0031 × 28) = 6.99 + 0.09 = 7.08 mL/dL
DO2  = 12.10 × 3.8 × 10 = 459.8 mL/min
VO2  = 3.8 × (12.10 − 7.08) × 10 = 190.8 mL/min
O2ER = (12.10 − 7.08) / 12.10 = 0.41

This patient has a low DO₂ driven primarily by anaemia (Hb 9), a cardiac output that is below normal, and an extraction ratio of 0.41 — elevated above normal, meaning the tissues are working hard to compensate. The haemoglobin is the most correctable deficit.

Watch trends, not single numbers

A single set of values is less informative than trending. A rising extraction ratio or falling SvO₂ over hours in a resuscitating patient tells you whether your interventions are improving tissue oxygen balance, even before other parameters change. Serial measurement after each intervention — transfusion, fluid bolus, vasopressor, ventilator adjustment — is how these calculations earn their place in the ICU.

Treat the dissolved-oxygen term as minor at normal pressures but real in severe anaemia or high-FiO₂ states.