Acid-base balance


Martina Feichter

Martina Feichter studied biology in Innsbruck with an optional subject in pharmacy and also immersed herself in the world of medicinal plants. From there it was not far to other medical topics that still captivate her today. She trained as a journalist at the Axel Springer Academy in Hamburg and has been working for lifelikeinc.com since 2007 - first as an editor and since 2012 as a freelance author.

More about the lifelikeinc.com experts Acid-base balance is a complex interaction of different systems, with which the body ensures a constant pH in the body. With the help of several so-called buffer systems in the blood, excessive deviations are corrected. Find out what the acid-base balance tells you about your health.

Article overview acid-base balance

  • What is the acid-base balance?
  • When do you determine the acid-base balance?
  • Normal values
  • When are the values ​​of the acid-base balance too low?
  • When are the values ​​of the acid-base balance too high?
  • What to do if the acid-base balance changes?

What is the acid-base balance?

The acid-base balance (sometimes referred to as the base balance) is composed of various buffer systems and ensures that the body can regulate fluctuations in the pH value in a targeted manner. This means that if the pH is too low (acidic), bases are absorbed or formed and acids are eliminated. If the pH is too high (basic or alkaline), acids are absorbed or formed and bases are eliminated.

Open and closed buffer systems

It is important to distinguish between open and closed buffer systems. Open buffer systems are capable of transporting excess acids or bases out of the body. The most important one here is the bicarbonate buffer system, in which acidic substances can be exhaled via the lungs as carbon dioxide (CO2). The ammonium buffer system excretes acids via the kidneys.

In contrast, with closed buffer systems, all acidic and basic substances remain in the body. By binding them to other substances, the body can also regulate the pH in this way. For example, in the case of the protein buffer system, the red blood pigment (hemoglobin) or the blood albumin also absorbs the acidic hydrogen ions (H +).

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When do you determine the acid-base balance?

The doctor determines the acid-base balance mostly on the pH of the blood. Together with the other blood gas values ​​- oxygen (O2), carbon dioxide (CO2), base excess (BE) and bicarbonate (HCO3) - he gets an overview of the performance of the lungs, the heart and the buffer systems. Disorders of the kidney also influence the acid-base balance and are reflected in changed measurements.

Above all, it is important that the doctor correctly indicates the cause of a deviation of the pH value. We distinguish disorders that arise from the metabolism (metabolic disorders) of those that emanate from the lungs (respiratory disorders). In each case, the still functioning system tries to normalize the pH again. For example, the lungs intervene in a metabolic disorder.

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Acid-base balance - normal values

To determine the blood gas levels and thus the acid-base balance, the doctor usually takes a small blood sample from an artery. For the evaluation of the acid-base balance, especially the pH, the partial pressure of the carbon dioxide (pCO2), the standard bicarbonate (HCO3) and the base excess (BE) are used. The base excess indicates whether there are too many or too few basic substances in the blood. For adults, the following normal values ​​apply:


normal range

PH value

7,36 - 7,44

pCO2 value

35 - 45 mmHg

Standard bicarbonate (HCO3-st.)

22-26 mmol / l

Base excess

-2 to +2 mmol / l

The values ​​must always be assessed in conjunction with the reference values ​​of the respective laboratory, which is why deviations are possible. For children and adolescents other normal values ​​apply.

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When are the values ​​of the acid-base balance too low?

If the doctor measures too low pH, it is called acidosis. This means that the body is unable to convert acidic substances or expel them, for example via the lungs or kidneys. Carbon dioxide partial pressure, bicarbonate and base excess readings help to find the cause:

Simplified, carbon dioxide increases when the cause is respiratory (respiratory acidosis). This is the case with impaired respiration (hypoventilation), for example due to a lung disease such as asthma.

If, on the other hand, the bicarbonate is too low, it is a metabolic acidosis. In most cases, a so-called ketoacidosis is caused by a derailed type 1 diabetes mellitus. The acidity increases, however, even when fasting or in a malfunction of the kidney (renal insufficiency).

In the worst case, both the carbon dioxide is increased and the bicarbonate lowered. In this combined acidosis, the body is no longer able to regulate the pH itself. The cause may be a multi-organ failure.