Arterial Blood pH Calculator

You may find it surprising, but a significant amount of gas is dissolved in your blood serum. We can assess it by examining an arterial blood sample. The parameters measured in the arterial blood gas test are:

• Arterial oxygen partial pressure (PaO₂);
• Arterial carbon dioxide partial pressure (PaCO₂);
• Bicarbonate (HCO₃⁻);
• Total CO2 (tCO₂); and
• Base excess (BE).

One of the most important pieces of information that we can gain from the blood gas values is blood pH. The pH is a measure of acidity or alkalinity of any solution.

Normal pH value ranges for arterial blood are 7.35-7.45, while the normal pH of venous blood is 7.31-7.41. 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.

If the calculated pH is lower than the norm, it indicates acidosis, and if it's higher – it informs us about alkalosis. To learn more about pH, visit our pH calculator.

These states of acid-base imbalance can be symptoms of respiratory or metabolic disorders. The body's acid-base homeostasis is a highly complex system – you can read more in the article published in the Journal of Clinical & Diagnostic Research.

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) ]