Venous Blood pH Calculator

Created by Małgorzata Koperska, MD
Reviewed by Bogna Szyk and Steven Wooding
Based on research by
Hills A. G. pH and the Henderson-Hasselbalch equation The American Journal of Medicine (August 1973)
Last updated: Feb 02, 2023

The venous blood gas calculator estimates the venous blood pH using bicarbonate (HCO₃) values 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.

We try our best to make our Omni Calculators as precise and reliable as possible. However, this tool can never replace a professional doctor's assessment. If any health condition bothers you, consult a physician.

💡 With our Henderson-Hasselbalch calculator, you can calculate the pH of a buffer solution using the Henderson-Hasselbalch equation.

What can you calculate using venous blood gas levels?

Among the most important information we can gain from blood gas values is the pH of the blood. 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 acidic carbon dioxide (CO₂) in the venous blood.

When the calculated pH is lower than the norm, it indicates acidosis, and when it's higher, it indicates alkalosis. These states of acid-base imbalance can be a symptom of respiratory or metabolic disorders. Acid-base homeostasis is a highly complex process in the body. If it's an exciting topic for you, you can read more about it, e.g., in the article published in Journal of Clinical & Diagnostic Research.

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 / (0.0308 × PaCO₂)]

Małgorzata Koperska, MD
Bicarbonate (HCO₃)
Carbon dioxide partial pressure (PaCO₂)
Venous blood pH
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