Respiratory

O₂ Extraction Ratio Calculator

Share of delivered oxygen that the tissues take up; rises when delivery falls or demand climbs.

Reviewed by Alex G, BSN, RN, CEN, CCRN, CMC, NREMT-P · From the Reference tab of the app

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Formula

(VO2 / DO2) * 100

Reference: About 25% at rest

How it is used

• Normal extraction at rest is about 25%: a DO₂ near 1,000 mL/min against a VO₂ of about 250 mL/min, leaving SvO₂ near 70–75%.
• Extraction rises when delivery falls or demand rises; once it can rise no further, tissues turn to anaerobic metabolism and lactate climbs.
• A low extraction with a high SvO₂ in shock means the cells are not taking up oxygen: sepsis with microcirculatory shunting, cyanide or carbon monoxide, or a wedged catheter.

Same formula as the app. Open it in the web app.

Related one-pagers

• Shock Types at a GlanceEvery shock type ends in the same place: oxygen delivery (DO₂) falls below what the tissues consume (VO₂), or the cells cannot use what arrives. CaO₂ = (1.34 × Hb × SaO₂) + (0.003 × PaO₂), about 20 mL/dL. DO₂ = CO × CaO₂ × 10, about 1,000 mL/min (DO₂I 500–600 mL/min/m²). Resting VO₂ is about 250 mL/min, so the oxygen extraction ratio (O₂ER = VO₂ ÷ DO₂) is about 25% and SvO₂ sits near 70–75%.
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Related calculators

• A-a Gradient
• Alveolar Gas Equation (PAO₂)
• Arterial Oxygen Content (CaO₂)
• Dead Space Fraction (Bohr)
• Driving Pressure
• Dynamic Compliance
• Minute Ventilation
• Oxygen Consumption (VO₂)

For education and exam preparation only. Follow your institution’s protocols. For education and exam preparation only. Verify results independently and follow your institution’s protocols. Not a substitute for clinical judgment.