Blood gas values


Eva Rudolf-Mueller

Eva Rudolf-Müller is a freelance author at lifelikeinc.com. She studied human medicine and journalism and worked in both areas - as a doctor in the clinic, as a reviewer, as well as a medical journalist for various journals. Currently, she works in online journalism, where a wide range of medicine is offered to all.

More about the lifelikeinc.com experts Blood gas values indicate how much oxygen (O2) and carbon dioxide (CO2) are in the blood. In addition, the base excess (BE), the pH value and the bicarbonate (HCO3) are also measured. With the help of the blood gas values, the doctor can monitor the lungs and the heart - and thus the respiration and the supply of the body, especially with oxygen. Learn here what the blood gas values ​​tell you about your health.

Article overview blood gas values

  • What are blood gas values?
  • When do you determine the blood gas values?
  • normal values
  • When are the blood gas levels too low?
  • When are the blood gas levels too high?
  • What do you do with altered blood gas levels?

What are blood gas values?

Through the lungs we can exhale oxygen (O2) and exhale carbon dioxide (CO2). Our blood in the lungs absorbs the O2 - the oxygen partial pressure (pO2 value) in the blood rises (this reflects the amount of dissolved O2 in the blood). The heart pumps the oxygen-rich blood through the body. In the various tissues and organs, the cells can absorb the oxygen from the blood and use it for energy. This creates CO2, which is released into the blood and transported to the lungs, where we exhale it. As a result, the proportion of dissolved carbon dioxide in the blood (carbon dioxide partial pressure, pCO2 value) decreases again.

If there is a disturbance of the lung or heart function, the doctor can detect this on the basis of the blood gas values. Especially in patients who are being treated in intensive care units, regular measurements of blood gas values ​​help with monitoring.

In addition to the pO2 value and the pCO2 value, the acid-base balance is also measured by means of the base excess (BE) and the pH and the bicarbonate (HCO3). The blood gas values ​​thus also provide information as to whether the blood is too acidic or too basic and whether the body can compensate for the condition.

Acid-base balance

If you want to know more about the topic, read the article acid-base balance.


Everything important about HCO3 can be found in the article Bicarbonate.

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When do you determine the blood gas values?

The doctor will determine the blood gas levels for evidence of heart and lung function and kidney function (the kidneys play an important role in the acid-base balance). With the help of blood gas values ​​both respiratory and metabolic diseases can be detected. However, this measurement is usually required only for seriously ill people.

The following causes can be hidden behind altered blood gas values:

  • Diseases and dysfunction of the lungs
  • Diseases and disorders of the kidney
  • severe circulatory disorders
  • Metabolic disorders such as diabetes mellitus
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Blood gas values: normal values

To determine the blood gas levels, the doctor usually takes a small blood sample from an artery. For adults, the following normal values ​​apply:


normal range


75 - 100 mmHg

pCO2 value

35 - 45 mmHg

PH value

7,36 - 7,44

Base excess (BE)

-2 to +2 mmol / l

Standard bicarbonate (HCO3)

22-26 mmol / l

oxygen saturation

94 - 98 %

The values ​​must always be assessed in conjunction with the reference values ​​of the respective laboratory, which is why deviations are possible. Age also plays a role, so that different values ​​apply to children and adolescents.

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When are the blood gas levels too low?

Most of the time, the pO2 level is too low when there is not enough oxygen left in the lungs to be absorbed or distributed with the blood in the body. Typical diseases that cause this are asthma, COPD, heart disease and circulatory disorders.

Another reason for decreased blood gas levels may be too low an oxygen concentration in the breath. This can be observed, for example, with mountaineers who are traveling in high mountains. Increased consumption during physical exertion also lowers the pO2 level in the blood.

The carbon dioxide in the blood can sink if people breathe too much or too fast (hyperventilating). Since carbon dioxide is an acid component in the regulation of body pH, a high CO2 loss leads to basic blood. This is also referred to as respiratory alkalosis.