Using the Fick equation to calculate the arteriovenous difference and cardiac output

New to Fick’s law? In this short article, learn about how to calculate the arteriovenous difference and cardiac output.
Last update2nd Dec 2020

The amount of oxygen extracted from each aliquot of blood—tissue oxygen extraction or consumption—also differs among organ systems.

Figure 1. The amount of oxygen extracted from the blood by a tissue—tissue oxygen extraction—differs across organ systems.

Measurement of oxygen consumption per minute by a specific organ system would require determination of the oxygen content of venous blood draining that organ. In clinical practice, an overall measurement of oxygen utilization is determined by catheterization of the right heart and determination of mixed venous oxygen content (MVO2). The mixed venous oxygen content represents the weighted average of oxygen content in venous blood from all organ systems.

Become a great clinician with our video courses and workshops

The relationship among the variables related to oxygen consumption is expressed by the Fick principle: oxygen consumption is the product of cardiac output and the arteriovenous oxygen difference.

Figure 2. The Fick’s principle states that oxygen consumption is the product of cardiac output (CO) and the arteriovenous oxygen difference (CaO2 minus CVO2).

In the setting of a fixed cardiac output, increased oxygen demand results in an increased arteriovenous oxygen difference, and with reduced oxygen demand the arteriovenous oxygen difference declines.

That’s it for now. If you want to improve your understanding of key concepts in medicine, and improve your clinical skills, make sure to register for a free trial account, which will give you access to free videos and downloads. We’ll help you make the right decisions for yourself and your patients.

Recommended reading

  • Grippi, MA. 1995. “Gas exchange in the lung”. In: Lippincott's Pathophysiology Series: Pulmonary Pathophysiology. 1st edition. Philadelphia: Lippincott Williams & Wilkins. (Grippi 1995, 137–149)
  • Grippi, MA. 1995. “Clinical presentations: gas exchange and transport”. In: Lippincott's Pathophysiology Series: Pulmonary Pathophysiology. 1st edition. Philadelphia: Lippincott Williams & Wilkins. (Grippi 1995, 171–176)
  • Grippi, MA and Tino, G. 2015. “Pulmonary function testing”. In: Fishman's Pulmonary Diseases and Disorders, edited by MA, Grippi (editor-in-chief), JA, Elias, JA, Fishman, RM, Kotloff, AI, Pack, RM, Senior (editors). 5th edition. New York: McGraw-Hill Education. (Grippi and Tino 2015, 502–536)
  • Tino, G and Grippi, MA. 1995. “Gas transport to and from peripheral tissues”. In: Lippincott's Pathophysiology Series: Pulmonary Pathophysiology. 1st edition. Philadelphia: Lippincott Williams & Wilkins. (Tino and Grippi 1995, 151–170)
  • Wagner, PD. 2015. The physiologic basis of pulmonary gas exchange: implications for clinical interpretation of arterial blood gases. Eur Respir J45: 227–243. PMID: 25323225

About the author

Michael A. Grippi, MD
Vice Chairman, Department of Medicine | Pulmonary, Allergy, and Critical Care Division, Perelman School of Medicine, University of Pennsylvania, USA.
Author Profile