The venous blood gas calculator estimates the venous blood pH, using the values of bicarbonate (HCO₃) and arterial carbon dioxide partial pressure (PaCO₂) in the patient's blood. To do so, we apply the Henderson-Hasselbalch equation developed in 1908 by Dr. Lawrence Joseph Henderson and then improved by Dr. Karl Albert Hasselbalch.

If you'd like to estimate arterial blood pH and learn more about it, use our arterial blood pH calculator.

What can you calculate using venous blood gas levels?

Some of the most important information that can be gained from the blood gas values is blood pH. pH is a measure of acidity or alkalinity of any solution. Normal pH value ranges for venous blood are 7.31-7.41, while normal pH of arterial blood is 7.35 - 7.45. It means that venous blood is more acidic than arterial. It's due to the fact that there is more of the acidic carbon dioxide (CO₂) in the venous blood.

If the calculated pH is lower than the norm, it indicates acidosis, and if it's higher - informs us about alkalosis. These states of acid-base imbalance can be symptoms of respiratory or metabolic disorders. The body's acid-base homeostasis is a very complicated system - you can read more about it here.

Calculating venous blood gas with the Henderson-Hasselbalch equation

The formula developed by Dr. Henderson described the use of carbonic acid as a buffer solution. Then, Dr. Hasselbalch re-expressed that formula in a more complicated manner to study acid-base disorders, which resulted in the Henderson–Hasselbalch equation. It describes the pH as a measure of acidity in biological and chemical systems.

For medical use, it calculates the pH of the blood by inserting the HCO₃ (in mEq/L or mmol/L) and PaCO₂ (in mmHg or torr) values in the following formula:

pH = 6.1 + log10 ( HCO₃ / ( 0.0307 * PaCO₂ ) )

Małgorzata Koperska, MD

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Venous Blood pH Calculator