What is normal VO2 and how does it change in critical illness?

Normal resting VO2 is approximately 200–250 mL/min (or 120–160 mL/min/m² indexed). VO2 increases significantly in critical illness due to hypermetabolism from sepsis, fever, agitation, and increased work of breathing — values of 300–400 mL/min/m² are common. Interventions that reduce VO2 (sedation, paralysis, fever control, mechanical ventilation) can prevent supply-demand mismatch in patients with limited DO2.

When is the Fick method preferred over other cardiac output methods?

The direct Fick method using measured VO2 (expired gas analysis) and arteriovenous oxygen difference is the gold standard for cardiac output measurement. In practice, it requires specialized metabolic measurement equipment, so the indirect Fick method using an assumed VO2 (125 mL/min/m²) is commonly used with mixed venous samples. The method is especially valuable when thermodilution is unreliable (severe tricuspid regurgitation, intracardiac shunts, irregular rhythms).

Oxygen Consumption (VO2) Calculator

Calculate systemic oxygen consumption (VO2 = CO × (CaO2 − CvO2) × 10) using the Fick principle to assess metabolic demand and oxygen utilization in critically ill patients.

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Frequently Asked Questions

What is normal VO2 and how does it change in critical illness?

When is the Fick method preferred over other cardiac output methods?