Blood gas values

The blood gas values ​​such as po2 value and pco2 value provide information about lung and heart function. Read more about blood gas values!

Blood gas values

The 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. Using the blood gas values, the doctor can monitor the lungs and the heart - and thus also the respiration and the supply of the body, especially with oxygen. Learn here what the blood gas values ​​tell you about your health.

Product 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 absorbs O2 in the lungs - 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 the excess of the base (BE) and the pH and the bicarbonate (HCO3). The blood gas values ​​also provide information on 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.

When do you determine the blood gas values?

The doctor determines the blood gas levels to get information about 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 dysfunctions of the lungs
  • Diseases and disorders of the kidney
  • severe circulatory disorders
  • Metabolic disorders such as diabetes mellitus

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.

When are the blood gas levels too low?

In most cases, the pO2 level is too low, if not enough oxygen can be taken in via the lungs or distributed with the blood in the body. Typical conditions that cause this include asthma, COPD, heart disease and circulatory disorders.

Another reason for reduced 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 exercise expenditure 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, high CO2 loss leads to basic blood. This is also referred to as respiratory alkalosis.

When are the blood gas levels too high?

While exhaling a lot of CO2 during a hyperventilation, one simultaneously enriches the blood with O2. An increase in the oxygen content in the respiratory air causes an increase in the pO2. This can be used for anesthesia.

The pCO2 value is often increased when the pO2 value is lowered. By reducing the respiratory effort, the CO2 accumulating in the body can no longer be exhaled. This is also called respiratory global insufficiency. In addition, since the carbon dioxide in the blood lowers the pH and thus acidifies the body, this condition is called respiratory acidosis.

What do you do with altered blood gas levels?

Depending on the cause, the doctor will take different measures to normalize the patient's blood gas levels.

For example, if the doctor is seeking to increase the pO2, he will prescribe medication for asthma or COPD to improve the patient's breathing performance. Physiotherapy and breathing exercises are also helpful and additionally reduce elevated pCO2 levels. An enrichment of the breathing air with oxygen should only take place in an emergency.

Against low pCO2 levels in hyperventilation, it often helps to breathe in and out of the patient.

Generally speaking, all possible causes of a change in the Blood gas values must be reviewed and treated.

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