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A blood gas test (ABG arterial blood test) is a test that measures the amount of oxygen and carbon dioxide in the blood, as well as the acidity (pH) of the blood. The ABG analysis evaluates how efficiently the lungs supply oxygen to the blood and how efficiently they remove carbon dioxide from it. The test also shows how well the lungs and kidneys work together to maintain normal blood pH (acid-base balance). Blood testing is typically done to evaluate respiratory conditions and other conditions that can affect the lungs, and to manage the health of patients receiving oxygen therapy (respiratory therapy). In addition, the acid-base component of the test contains information about kidney function.
What is a blood gas analysis?
The test is performed on blood from an artery. It measures partial pressure and carbon dioxide in the blood, as well as oxygen content, oxygen saturation, bicarbonate content and blood pH. Oxygen in the lungs is carried to the tissues via the bloodstream, but only a small amount can actually be dissolved in the arterial blood. The amount of this gas depends on the partial pressure of oxygen (the pressure that the gas exerts on the walls of the arteries). Therefore, oxygen partial pressure testing actually measures how much oxygen is delivered to the lungs through the blood.
Carbon dioxide is released as a by-product of cellular metabolism. Its partial pressure indicates how well the lungs eliminate this carbon dioxide. The rest of the oxygen, which does not dissolve in the blood, combines with hemoglobin, a combination of protein and iron found in red blood cells. The measurement of oxygen content in the ABG assay shows how much oxygen combines with hemoglobin. An important indicator is oxygen saturation, which compares the amount of oxygen actually bound to hemoglobin and the total amount of oxygen.
How is the procedure?
There is no special preparation for the procedure. Patients are not given any restrictions on drinking or eating before the test. The oxygen concentration should remain unchanged for 20 minutes prior to analysis; if the test is to be performed without oxygen saturation, the gas must be turned off for 20 minutes prior to the test. During the test, the patient should breathe normally. A blood sample is obtained by arterial puncture (usually in the wrist, although it may be in the groin or arm). If a puncture is required, the skin over the artery is cleaned with an antiseptic. The doctor then draws blood using a small, sterile needle attached to a disposable syringe. The patient may feel a short pulsation or cramps at the puncture site. Once the material has been collected, it should be taken to the laboratory for analysis as soon as possible.
After the blood has been drawn, the doctor or patient presses the cotton wool over the puncture site for 10-15 minutes to stop the bleeding, and then wraps it tightly with a bandage. The patient should rest calmly after the procedure is completed. Health care providers will watch for signs of bleeding or circulatory problems. The risks of getting them when the test is performed correctly are very low. Include bleeding or bruising at the site of blood donation or after some time. Very rarely, there may be a problem with circulation in the area of the puncture.
Test results
The results of the analysis consist of several indicators that will help determine how efficiently the blood system is functioning. They also express the level of saturation of the body with oxygen, which is very important for internal organs. The main criteria are:
Partial pressure (PP)
Partial pressure is a way of estimating the number of molecules of a particular gas in a mixture of gases. This is the amount of pressure of a particular gas in the total pressure. For example, we normally breathe air that has a pressure of 100 kPa at sea level, oxygen is 21% of 100 kPa, which corresponds to a partial pressure of 21 kPa. When testing blood gases, Henry’s law is used to determine the partial pressures of gases in the blood. This law states that when a gas dissolves in a liquid, the partial pressure (i.e. the concentration of the gas) within the liquid is the same as that of the gas in contact with the liquid. Therefore, the partial pressure of gases in the blood can be measured. You will see a column labeled PaO2 – partial pressure of oxygen in arterial blood and PaCO2 – partial pressure of carbon dioxide.
Basic Excess (BE)
This is the amount of strong base that must be added or subtracted from a substance to bring the pH back to normal (7.40). A value outside the normal range (-2 to +2) indicates a metabolic cause of acidosis or alkalosis.
Bicarbonate (HCO3)
Bicarbonate is produced by the kidneys and acts as a buffer to maintain pH. The normal range for bicarbonate is 22-26 mm/L. If there are additional acids in the blood, the bicarbonate level will drop as the ions are used to buffer those acids. If there is chronic acidosis, slightly more bicarbonate is produced by the kidneys to keep the pH normal. It is for this reason that elevated bicarbonate can be observed in chronic respiratory failure type 2, when the pH remains normal despite elevated CO2.
Electrolytes
A venous or arterial gas test is a good way to quickly check your potassium and sodium levels. This is especially important in the direct treatment of cardiac arrhythmias, as it gives an immediate result.
Lactate
Produced as a by-product of anaerobic respiration. Elevated lactate can be caused by any process that causes tissue to use anaerobic respiration. This is an effective indicator of poor tissue perfusion.
Glucose
Glucose is especially important in the treatment of a patient who suffers from loss of consciousness or frequent convulsions. It is also necessary for patients with suspected diabetes. Glucose may be elevated in patients with severe sepsis or other metabolic stress.
Other Analysis Components
They are rarely violated and often overlooked. However, it is important to notice if they are out of the norm. This is especially true in the case of carbon monoxide, as there may be other people at risk.
Carbon monoxide (CO)
Usually SD is 10% indicate poisoning, usually from poorly ventilated boilers or old heating systems. At levels of 10-20%, symptoms such as nausea, headache, vomiting and dizziness will be observed. At higher levels, patients may experience arrhythmia, cardiac ischemia, respiratory failure, and mild convulsions.
Analysis efficiency
Testing guarantees almost one hundred percent data on the functioning of your body’s circulatory system. If errors occur, then, most often, due to the inattention of the staff. The effectiveness of the delivery of the analysis and the result directly depends on the accuracy of the medical officer. Blood gas testing is often subject to the risk of errors caused by improper sampling, transport and storage. Therefore, laboratories should follow specific guidelines to prevent potential errors due to improper sample handling.
The test must be performed by trained laboratory personnel. The competence of staff responsible for blood testing should be assessed for new hires and qualifications reassessed annually. This will guarantee a more accurate result. The time of delivery of the sample to the central laboratory must be recorded. The time between sampling and analysis should not exceed 30 minutes. If the time exceeds the recommended interval, it is necessary to inform the clinical staff who will analyze the blood.
To avoid misunderstandings and confusion, the patient must ask the container with his material to sign or securely stick a mark with a surname. Before testing, the person responsible for sample analysis should check the details on the label against the data on the test form to confirm patient identification. If the sample needs to be immersed in an ice suspension (a mixture of ice and water) until analysis is complete (i.e. if a delay of more than 30 minutes is expected), the integrity of the labels must be protected even during immersion.
The procedure itself is also important. Correct results are guaranteed if the exact course of analysis is followed. The quality of the whole blood sample must be checked before the test. Blood samples containing air bubbles or visible clots are unacceptable for analysis. Proper mixing of whole blood samples is critical to obtaining accurate hemoglobin results. Capillary samples should be mixed using a metal rod and a magnet. The magnet should be moved from end to end along the capillary until the components are evenly distributed (homogenized) or at least 5 seconds. One end of the capillary should be opened by carefully removing the sealant cap. The metal rod must be removed by slowly pulling the magnet over the capillary, being careful not to spill blood or introduce air into the sample. Before introducing the sample into the analyzer, the opposite end of the capillary should be opened by removing the remaining sealant cap. The sample must be run all the way through to remove entrapped air.
Blood gas analysis is an effective method for checking the circulation of oxygen in the blood. It will not identify specific diseases, but will show if they can manifest themselves in the future. An oxygenated body functions better, and the number of health complaints is significantly reduced. According to doctors, for a complete diagnosis of the body, from time to time, an analysis of the gas composition of the blood should be carried out.