The Henderson Hasselbalch equation describes the relationship between pH, base and acid. The more acid in the system, the lower the pH. The more base or alkali in the system, the higher the pH.

The simplified version of the Henderson-Hasselbach equation above is really important to remember when interpreting blood gases. If the blood is more acidic than the normal range, this could be because there is too much carbon dioxide in the blood or too much alkali, or a combination of these. If the blood is more alkalotic than the normal range, this could be because there is too much bicarbonate in the blood or too little acid, or a combination of these.