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The ABG is a medical test which main objective measure oxygen levels and carbon dioxide in blood. A technique that allows determining the presence of certain respiratory diseases.

In this article we will see exactly what this test consists of, how it is done and how to interpret the results of it.

What is blood gas?

Gasometry is a very popular diagnostic test that consists of the collection of venous or arterial blood , which is analyzed in the laboratory to determine the levels of oxygen, carbon dioxide, and other substances present in the blood. It is generally used to diagnose different disorders that cause respiratory failure.


Two types of blood gas are differentiated.

  • Venous: in this case a blood sample is collected from a certain vein in the body; the procedure is exactly the same as a routine blood test. It is used to know what the pH levels are, as well as bicarbonate.
  • Arterial: to perform this test, blood is collected from a specific artery, usually the radial artery of the wrist. It really is the only blood that allows you to accurately determine the amount of oxygen that passes from the lungs to the blood. That is why this type of blood gas is the one most commonly performed to diagnose cases of respiratory induction.

Values ​​that are measured in blood gases

In this medical test, a set of values ​​of different substances present in the blood are measured.

  • pO2: it is known as the partial pressure of oxygen, that is, the amount of dissolved oxygen in the blood. Normal values ​​range from 75 mmHg to 100 mmHg. Those values ​​below 60 mmHg imply that there is respiratory failure.
  • pCO2: refers to the partial pressure of carbon dioxide, the amount of dissolved carbon dioxide present in the blood. Normal results range from 35 mmHg to 45 mmHg.
  • Blood pH: it is one of the most important values, which consists of the analysis of the amount of protons dissolved in the blood, which provide a certain degree of acidity to the plasma. Normal values ​​are between 7.35 and 7.45.
  • SatO2: oxygen saturation is the most determining value for diagnosing respiratory failure. Normal values ​​range from 95-100%.
  • HCO3: and finally, the amount of bicarbonate present in the blood. In this case, normal values ​​are between 22-28 mEq.

Why is a blood gas done?

As we have pointed out, this is a diagnostic test that is used relatively frequently since it is minimally invasive and can be very useful for detecting conditions that cause respiratory failure.


The asthma is a chronic disease affecting the airways , whose walls are inflamed and constricted . In this way, there is a situation of respiratory failure, which is accompanied by other symptoms such as cough and pressure in the chest.

An asthma attack occurs when the symptoms of the disease get worse. In the vast majority of cases it is a condition that requires urgent medical attention.

Pulmonary fibrosis

Pulmonary fibrosis is known as a disorder caused by damage to the lung tissue , which thickens, making it impossible for the lungs to function properly.

Damage to lung tissue cannot be repaired in any way. However, today there is a wide range of medical treatments, medications and therapies, which greatly alleviate symptoms, and therefore improve the quality of life of patients.

Pulmonary edema

A disease that arises from an excessive accumulation of fluid in the lungs , thus making it difficult to breathe. In a high percentage of cases, pulmonary edema is mainly caused by a heart disorder, although fluid can accumulate for other reasons as well.

It manifests itself suddenly and requires immediate medical attention since life is at risk. Treatment varies depending on the cause, but almost always consists of oxygen and medication.


In those cases in which a person breathes too quickly, and in addition to agitation, he can expel more carbon dioxide than he really should , thus reducing the amount of this substance present in the blood. A situation that produces alterations in blood pH.


The sepsis is a disease of a serious nature. It occurs when chemicals released into the blood to fight a certain infection lead to widespread inflammation . A situation that leads to the formation of clots, thus reducing blood flow, and depriving both organs and tissues of nutrients and oxygen.

Without proper treatment, different organs of the body can begin to fail. In the most severe cases, the heart gradually weakens, leading to what is known as septic shock.

Renal metabolism disorder

And finally, various alterations in renal metabolism may require a blood gas test. Do not forget that the functioning of the lungs and kidneys is closely related.

How is a blood gas done?

Blood gas is a relatively simple medical test, performed in a short period of time; a small prick is enough to extract a tube of blood , which usually does not take more than a few minutes.

No prior preparation is necessary; fasting is not even necessary. However, it is important to inform the doctor about all the medications that are being taken since, for example, diuretics can alter the results of the test.


Once the patient comes to the consultation, first the doctor asks a series of general questions about his medical history; If you suffer from any type of chronic disease, what is your lifestyle … Of course, also about the symptoms that led to the performance of this test.

A healthcare professional then proceeds to draw the blood needed for the test . Depending on the type of blood gas in question, blood must be drawn from one place or another. As we have pointed out, the most common is that it is an arterial blood gas, in which case the blood must be drawn from the radial artery, located in the wrist. If it is a venous blood gas, the blood is drawn from the front of the elbow, like a common blood test.

Before proceeding with the extraction of blood, it is essential to clean the surface of the skin with an antiseptic substance to avoid germs. He then punctures with a sterile needle and collects the sample.

Finally, a cotton ball is placed on the puncture site, which must be pressed for between 10 and 15 minutes to stop bleeding and prevent bruising.


Like any other medical test, blood gas has a number of complications that are interesting to know about. It is worth noting that this is a very low risk test and that complications are rare.

  • Local infection: whenever a needle is pierced through the skin, there is a certain risk of infection. However, today it is very rare that it occurs in the medical field since the measures are extreme to the maximum.
  • Hematoma: It is relatively common for a little blood to leak from the punctured artery into the surrounding tissues. To avoid this complication, it is important to press down on the cotton that the healthcare staff places after the extraction.
  • Hemorrhage: a complication that occurs in a very low percentage of cases since the puncture needle is very fine.


Gasometry is a very common diagnostic test as it is very simple to perform and allows the diagnosis of a wide range of disorders that cause respiratory failure . Although abnormal refusals can occur from lung disorders, they can also occur from kidney or metabolic disorders.

Through the results of the blood gas, the doctor will be in charge of making a diagnosis and, if he considers it appropriate, of requesting additional medical tests.

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Hello Readers, I am Nikki Bella a Psychology student. I have always been concerned about human behavior and the mental processes that lead us to act and think the way we do. My collaboration as an editor in the psychology area of ​​Well Being Pole has allowed me to investigate further and expand my knowledge in the field of mental health; I have also acquired great knowledge about physical health and well-being, two fundamental bases that are directly related and are part of all mental health.

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