Blood gas levels
and Eva Rudolf-Müller, doctorValeria Dahm is a freelance writer in the medical department. She studied medicine at the Technical University of Munich. It is particularly important to her to give the curious reader an insight into the exciting subject area of medicine and at the same time to maintain the content.
More about the expertsEva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.
More about the experts All content is checked by medical journalists.The blood gas values provide information on how much oxygen (O2) and carbon dioxide (CO2) is in the blood. In addition, the base excess (BE), the pH value and the bicarbonate (HCO3) are measured. With the help of the blood gas values, the doctor can monitor the lungs and the heart - and thus also the breathing and the supply of the body, especially with oxygen. Find out here what blood gas values can tell you about your health.
What are blood gas levels?
We can inhale oxygen (O2) and exhale carbon dioxide (CO2) through the lungs. Our blood absorbs the O2 in the lungs - the oxygen partial pressure (pO2 value) in the blood increases (this reflects the amount of dissolved O2 in the blood). The heart pumps the oxygen-rich blood around the body. In the various tissues and organs, the cells can absorb oxygen from the blood and use it to generate energy. This creates CO2, which is released into the blood and transported to the lungs, where we exhale it. This reduces the proportion of dissolved carbon dioxide in the blood (carbon dioxide partial pressure, pCO2 value) again.
If there is a disorder of the lung or heart function, the doctor can recognize this on the basis of the blood gas values. Regular measurements of blood gas values are particularly helpful in monitoring patients who are being treated in intensive care units.
In addition to the pO2 value and the pCO2 value, the acid-base balance is also measured via the base excess (BE) and the pH value as well as 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.
Bicarbonate
You can find out everything you need to know about HCO3 in the article Bicarbonate.
When do you determine the blood gas values?
The doctor determines the blood gas values in order to obtain information about the function of the heart, lungs and kidneys (the kidneys play an important role in the acid-base balance). With the help of the blood gas values, both respiratory and metabolic diseases can be recognized. However, this measurement is usually only required for the seriously ill.
The following causes can be hidden behind changed blood gas values:
- Diseases and dysfunction of the lungs
- Diseases and dysfunction of the kidney
- severe circulatory disorders
- Metabolic disorders such as diabetes mellitus
Blood gas values: normal values
To determine blood gas levels, the doctor usually takes a small sample of blood from an artery. The following normal values apply to adults:
|
parameter |
Normal range |
|
pO2 value |
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 different values apply to children and young people.
When are the blood gas levels too low?
The pO2 value is usually too low when enough oxygen can no longer be absorbed via the lungs or distributed in the body with the blood. Typical diseases that cause this are asthma, COPD, heart disease and circulatory disorders.
Another reason for decreased blood gas values can be too low a concentration of oxygen in the air you breathe. This can be observed, for example, in mountaineers who are out and about in high mountains. Increased consumption during physical exertion also lowers the pO2 value in the blood.
The carbon dioxide in the blood can decrease when people breathe too hard or too fast (hyperventilating). Since the carbon dioxide is an acidic component in the regulation of the pH value in the body, a high loss of CO2 leads to basic blood. This is also referred to as a respiratory alkalosis.
When are the blood gas levels too high?
While you exhale a lot of CO2 during hyperventilation, you enrich your blood with O2 at the same time. An increase in the proportion of oxygen in the air you breathe also causes an increase in pO2. This is used, for example, with anesthesia.
The pCO2 value is often increased when the pO2 value is decreased. Due to a reduction in breathing capacity, the CO2 accumulating in the body can no longer be exhaled. This is also called global respiratory failure. Since the carbon dioxide in the blood lowers the pH value and thus acidifies the body, this condition is called respiratory acidosis.
What do you do if your blood gas values change?
Depending on the cause, the doctor will take different measures to bring the patient's blood gas levels back to normal.
If the doctor aims to increase the pO2 value, for example, he will prescribe medication for asthma or COPD, which should improve the patient's respiratory performance. Physiotherapy and breathing exercises are also helpful and also reduce increased pCO2 values. Enriching the breath with oxygen should only take place in an emergency.
Against reduced pCO2 values during hyperventilation, it often helps to let the patient inhale and exhale into a bag.
As a general rule, if there is a change in blood gas values, all possible causes must be checked and treated.
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