Arterial or Venous Blood Gas
An arterial or venous blood gas test is used to measure the concentration of gases in the blood, acidity, and pH. This information is useful for assessing the presence of respiratory diseases or monitoring patients with kidney or heart issues.
General Description
Blood gas analysis is a diagnostic test performed in a laboratory to determine the concentration of gases in the blood (usually oxygen and carbon dioxide), acidity (acid-base balance), or pH level.
There are two types of blood gas tests depending on where the blood is taken from:
- Arterial Blood Gas: This is the most common test, where blood is drawn from the arteries, which carry oxygen-rich blood from the lungs to other parts of the body. It helps evaluate the lungs' ability to exchange gases, making it useful for diagnosing respiratory diseases.
- Venous Blood Gas: Blood is taken from the veins, which return oxygen-depleted blood to the lungs with higher levels of CO2. This test helps assess if the levels of gases in the blood are appropriate and if there is acid-base balance. It is used to detect respiratory or endocrine diseases, such as diabetes, and is useful for evaluating cellular oxygenation.
When is it indicated?
Blood gas analysis is performed when a respiratory disease is suspected, which hinders the exchange of gases in the lungs, such as respiratory failure, chronic obstructive pulmonary disease (COPD), asthma, or cystic fibrosis.
It is also commonly used in preparation for abdominal or thoracic surgeries, to monitor the progress of lung diseases, to assess the effectiveness of oxygen therapy treatments, or to check the acid-base balance in patients with kidney or heart failure, severe infections, or uncontrolled diabetes.
Typically, patients undergoing a blood gas test exhibit some of these symptoms:
- Rapid or uncontrolled breathing.
- Nausea and vomiting.
- Fatigue.
- Dizziness.
- Arrhythmia (heart rhythm disorders).
- Exposure to harmful substances like smoke, dust, or chemicals.
How is it performed?
The procedure for performing a blood gas test is simple; it involves drawing blood from a blood vessel:
- Arterial Blood Gas: The sample is taken from an artery, usually from the wrist, groin, or arm. To minimize discomfort, a topical anesthetic is applied before inserting the needle, as this procedure tends to be more uncomfortable than venous blood collection.
- Venous Blood Gas: This is performed similarly to routine blood tests, where a needle is inserted into a vein in the arm to obtain a blood sample.
The samples are analyzed in the laboratory, where the levels of oxygen, carbon dioxide, and pH are evaluated to ensure they are within the correct range.
Risks
Blood gas analysis is a safe test that does not pose a significant health risk.
However, bruising may occur at the site where the sample was taken, as excess blood can leak from the vessel and accumulate under the skin.
What to expect from a blood gas test
The blood gas test is an outpatient procedure, and normal activities can be resumed immediately afterward.
Although the procedure is not painful, a slight pinch may be felt during the venous blood gas when the needle is inserted. In arterial blood gas tests, the discomfort is alleviated with anesthesia. After the sample is taken, a bandage is applied, and it is recommended to apply pressure for five minutes to reduce the risk of bruising.
A blood gas test typically takes no more than 10 to 15 minutes.
The results are provided to the patient after a few days. Abnormal values may indicate issues with various body systems and diverse conditions, so a specialist should interpret them for accurate diagnosis.
Specialties that request blood gas tests
Arterial or venous blood gas tests are carried out in the specialties of Emergency Medicine, Pulmonology, Endocrinology, or Nephrology.
How to prepare
Before a blood gas test, you should avoid smoking and exposure to polluted air. The doctor may also advise discontinuing regular medication, especially anticoagulants.
Fasting is not necessary.
