What are blood gas levels?
We can breathe in oxygen (O2) and breathe out carbon dioxide (CO2) through our lungs:
Our blood absorbs the O2 in the lungs – the partial pressure of oxygen (pO2 value) in the blood increases (this reflects the amount of dissolved oxygen in the blood). The heart pumps the oxygen-rich blood throughout the body. In the various tissues and organs, the cells can absorb the oxygen from the blood and use it to generate energy. This produces CO2, which is released into the blood and thus transported to the lungs, where we exhale it. As a result, the amount of dissolved carbon dioxide in the blood (partial pressure of carbon dioxide, pCO2 value) decreases again.
If lung or heart function is disturbed, the doctor can detect this by looking at the blood gas levels. Especially in patients treated in intensive care units, regular measurements of blood gases help with monitoring.
Acid-base balance
If you want to know more about the topic, read the article Acid-Base Balance.
Bicarbonate
You can learn everything important about this laboratory value in the article Bicarbonate.
When do you determine blood gas levels?
The doctor determines the blood gas values to obtain indications of the heart and lung function as well as the kidney function (the kidneys play an important role in the acid-base balance). Blood gas values can thus be used to detect both respiratory and metabolic diseases. However, this measurement is usually only necessary for seriously ill patients.
The following causes can be hidden behind altered blood gas values:
- Diseases and dysfunctions of the lungs
- Diseases and dysfunctions of the kidneys
- 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 blood sample from an artery. For adults, the following normal values apply:
|
Normal range |
|
|
pO2 value |
71 – 104 mmHg |
|
pCO2 value |
Women: 32 – 43 mmHg |
|
pH value |
7,36 – 7,44 |
|
Base excess (BE) |
-2 to +2 mmol/l |
|
Standard bicarbonate (HCO3-) |
22 – 26 mmol/l |
|
94 – 98 % |
The values must always be assessed in conjunction with the reference values of the respective laboratory, which is why deviations from the stated values are possible. Age also plays a role, so different values are considered normal for children and adolescents.
When are blood gas values too low?
If the pO2 value is too low, the reason is usually that not enough oxygen can be absorbed via the lungs or distributed in the body with the blood. Typical diseases that cause this include:
Another reason for reduced blood gas values can be too low an oxygen concentration in the breathing air. This can be observed, for example, in mountaineers who are traveling in high mountains. Increased consumption during physical exertion also causes the pO2 value in the blood to drop.
When are blood gas levels too high?
While you exhale a lot of CO2 during hyperventilation, you simultaneously enrich the blood with O2. An increase in the proportion of oxygen in the air we breathe also causes an increase in pO2. This is used, for example, during anesthesia.
The pCO2 value is often increased when the pO2 value is decreased. A reduction in respiratory output means that the CO2 produced in the body can no longer be exhaled. This is also called respiratory global insufficiency. Since the carbon dioxide in the blood also lowers the pH value and thus acidifies the body, this condition is called respiratory acidosis.
What do you do if blood gas levels change?
To counteract reduced pCO2 values in hyperventilation, it is often helpful to have the patient breathe slowly in and out of a bag.
Generally speaking, the way in which altered blood gas values are treated in individual cases depends on their cause and their severity.
