Blood gas analysis (AGD) or arterial blood gas (ABG)test is a test to measure the level of oxygen, carbon dioxide, and the level of acid base (pH) in the blood.
Blood gas analysis is generally performed to check the function of the lungs, which are the site of exchange of oxygen and carbon dioxide. This test is also carried out on patients who are using a breathing apparatus to monitor the condition and determine whether the device settings are appropriate.
In addition, this test can be done to check the condition of the heart and kidneys, as well as check for symptoms caused by disturbances in the distribution of oxygen and carbon dioxide, or the pH balance in the blood, such as shortness of breath, difficulty breathing, nausea, dizziness, and decreased consciousness.
Indications for Blood Gas Analysis
Blood gas analysis is performed to determine if the blood is too acidic (acidosis) or alkaline (alkalosis), and to determine whether the oxygen pressure in the blood is too low (hypoxemia) or the carbon dioxide pressure is too high (hypercarbia).
The conditions above can be used as a basis for diagnosing diseases related to the body's metabolic system or respiratory system. These diseases include:
- Breathing failure
- Asthma
- Chronic obstructive pulmonary disease
- Pneumonia
- Diabetic ketoacidosis
- heart failure
- Heart failure
- Kidney failure
- Head or neck trauma that affects breathing, for example burns
- Severe infection or sepsis
- Sleep disturbance
- Chemical poisoning or drug overdose
In addition to diagnosis, blood gas analysis can also be used to evaluate the condition of patients who use breathing apparatus.
Warning Analystis Blood Gas
Blood samples for blood gas analysis come from arteries which are deeper than veins. Therefore, the technique of taking blood will be different from taking blood in general. This technique may also feel more uncomfortable.
Blood sampling can be done in several locations where the arteries are the easiest to access. However, there are several conditions that make arterial blood sampling not possible at a location, including:
- There is a blood flow disorder
- Have peripheral artery disease
- There is an abnormal channel (fistula) in the artery, either caused by disease or intentionally made or grafted for access to dialysis (cimino)
- There is an infection, burn, or scar
Patients need to tell their doctor if they have a blood clotting disorder or are taking blood thinning drugs (anticoagulants) to reduce the risk of bleeding. Patients also need to be informed of all medications, including herbal products, vitamins, and supplements that they are currently taking.
Several conditions can affect the results of the examination, including smoking or inhaling cigarette smoke (passive), having a fever, and breathing fast, for example because of anxiety.
Before Blood Gas Analysis
No special preparation needs to be made before undergoing a blood gas analysis. In some cases, the patient may only be asked to fast before the procedure.
Before taking blood, the doctor will determine which arteries are the easiest and qualify to be accessed. If needed, the doctor can run several types of tests to ensure smooth arterial blood flow.
If the patient is receiving supplemental oxygen, the oxygen level received should be constant for at least 20 minutes before the patient undergoes a blood gas analysis test. Supplemental oxygen supply can also be stopped 20 minutes before blood collection, if the patient's condition permits.
In certain conditions, the doctor can give a local anesthetic so that the patient does not feel pain when the needle is inserted into the artery.
Blood Gas Analysis Procedure
As a first step in a blood gas analysis, the doctor will sterilize the location for the blood sample, such as the wrist, elbow crease, or groin, with an antiseptic solution.
After finding the artery, the doctor will insert a needle into the vein. The amount of blood drawn is usually 3 mL or at least 1 mL.
After the blood sample is taken, the syringe will be slowly removed and the injection area will be covered with a bandage. To reduce the potential for swelling, the patient is advised to apply pressure to the injection site for several minutes after the needle is removed.
The blood sample will be immediately taken to the laboratory for analysis. For accurate results, the blood sample must be examined within 10 minutes of being drawn.
After Blood Gas Analysis
Because the arteries are quite sensitive, the patient may experience pain and discomfort during the blood draw for several minutes afterward. Patients are advised not to leave the room immediately so that the doctor can monitor the condition and possible side effects, such as dizziness, nausea, or fainting.
Usually, the patient can receive the test results about 15 minutes after the blood draw. The results will be explained by the doctor and the patient will be notified if further examination is needed.
Blood Gas Analysis Results
The results of a blood gas analysis depend on a number of factors, such as age, gender, and medical history. The results of this test generally include measurements of the following:
- Acid base (pH) of blood
Acid base or blood pH is measured by looking at the number of hydrogen ions in the blood. If the blood pH is below normal, the blood is said to be more acidic, while if the pH is above the normal value, the blood is said to be more alkaline.
- Oxygen saturation
Oxygen saturation is measured by looking at the amount of oxygen carried by hemoglobin in red blood cells.
- Oxygen partial pressure
The partial pressure of oxygen is measured based on the pressure of oxygen dissolved in the blood. This measurement determines how well oxygen can flow from the lungs into the blood.
- Partial pressure of carbon dioxide
The partial pressure of carbon dioxide is measured by looking at the pressure of carbon dioxide dissolved in the blood. This measurement determines how well carbon dioxide can be removed from the body.
- Bicarbonate
Bicarbonate is a balancing chemical that prevents blood pH from becoming too acidic or too alkaline.
Based on the measurements above, the results of the blood gas analysis are divided into normal and abnormal (abnormal). Here's the explanation:
Normal result
The results of blood gas analysis are said to be normal if:
- Blood pH: 7.38–7.42
- Oxygen absorption rate (SaO2): 94–100%
- Oxygen partial pressure (PaO2): 75–100 mmHg
- Partial pressure of carbon dioxide (PaCO2): 38–42 mmHg
- Bicarbonate (HCO3): 22–28 mEq/L
Abnormal results
Abnormal results can be indicators of certain medical conditions. The following are some of the medical conditions that can be detected through a blood gas analysis:
| blood pH | Bicarbonate | PaCO2 | Condition | Common Causes |
| <7,4 | Low | Low | Metabolic acidosis | Renal failure, shock, diabetic ketoacidosis |
| >7,4 | Tall | Tall | Metabolic alkalosis | Chronic vomiting, hypokalemia |
| <7,4 | Tall | Tall | respiratory acidosis | Lung disease, including pneumonia or chronic obstructive pulmonary disease (COPD) |
| >7,4 | Low | Low | respiratory alkalosis | Breathe quickly when in pain or anxiety |
Normal and abnormal range values generally vary, depending on the laboratory where the patient is undergoing blood gas analysis. This is because some laboratories use different measurements or methods in analyzing blood samples.
Consult the test results with the doctor for a detailed explanation. The doctor will determine whether the patient needs further examination or certain medication therapy.
Risks of Blood Gas Analysis
Blood gas analysis tests rarely cause side effects. Even if there are, the side effects experienced by patients are generally only mild, such as dizziness, pain, or bruising at the injection site for blood collection.
However, in certain cases patients can also experience more serious side effects, such as:
- Bleeding or swelling at the injection site
- Blood clots under the skin (hematoma)
- Faint
- Infection in the area of the skin that was injected