Introduction:
The blood gas analysis test, also known as arterial blood gas (ABG) analysis, is a test that measures the amount of oxygen, carbon dioxide, and pH of the blood. It evaluates how effectively the lungs deliver oxygen to the blood and how efficiently they remove carbon dioxide from the body. It simultaneously measures how the lungs and the kidneys interact to maintain acid-base balance in the blood.
If the pH becomes deranged, then normal cell metabolism is affected. It also provides information about kidney functions as well. The sample is usually withdrawn from an artery and ordered in case of emergencies.
The blood gas analysis is usually done to assess respiratory diseases and conditions that may affect the lungs. The procedure is being carried out to assess the effectiveness of the gaseous exchange and ventilation, whether spontaneous or mechanical. The arterial blood gas analysis assesses a patient's metabolic status. It is thus logical to request an ABG in patients who have the potential to become critically ill.
What does Arterial Blood Gas Measure?
The arterial blood gas analysis measures the following parameters:
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Oxygen content.
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The oxygen saturation level is the amount of oxygen the hemoglobin carries. It is measured with the help of pulse oximetry. It is considered normal if it is between 94 -100%.
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Hemoglobin levels.
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The partial pressure of oxygen is the pressure of oxygen dissolved in the blood.
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The partial pressure of carbon dioxide is the pressure of carbon dioxide dissolved in the blood.
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The pH of the blood is slightly alkaline with a normal pH of 7.35 - 7.45, and the body, specifically the lungs and kidneys, maintains the acid-base balance of the blood. The pH can be affected by the type of ions present, depending on the chemicals present in the fluid. A higher pH of more than 7.45 indicates that the blood is alkaline with more bicarbonate ions, whereas a lower pH of less than 7.35 indicates that the blood is acidic with more hydrogen ions.
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Bicarbonate (HCO3-) levels prevent the pH of the blood from becoming too acidic or too basic.
What Are the Indications of Arterial Blood Gas Analysis?
Healthcare may order an arterial blood gas analysis in the following cases:
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Acute Respiratory Distress Syndrome (ARDS): It is a life-threatening situation with excessively low levels of oxygen in the blood. Few conditions can cause sepsis and COVID-19.
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Severe Sepsis: A medical emergency can also be life-threatening. A response to an infection usually causes it.
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Septic Shock: It is caused by a response to an infection in which the blood pressure drops to dangerously low levels and eventually leads to multiple organ dysfunction syndrome and death.
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Hypovolemic Shock: It is characterized by a severe loss of blood, and the heart is unable to pump enough blood to meet the body's oxygen demands. It is also a medical emergency.
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Diabetic Ketoacidosis: It is typically seen in patients with uncontrolled diabetes, specifically in type-1 diabetes. It causes the blood to be acidic.
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Renal Tubular Acidosis: In patients with impaired kidney function, the kidney fails to remove acids from the blood into the urine, resulting in the blood becoming acidic.
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Acute Respiratory Failure: It is characterized by fluid accumulation around the alveoli and thus makes it difficult for the gaseous exchange.
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Acute Heart Failure: It is characterized by sudden weakening of the heart that limits its function.
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Cardiac Arrest: It can happen when the heart suddenly stops beating and pumping blood to the body. It requires immediate medical attention.
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Asthma: It is a chronic inflammatory disease characterized by hyperresponsiveness of the tracheobronchial smooth muscle to various stimuli, resulting in the narrowing of the airways along with increased secretion, mucosal edema, and mucus plugging. This makes it difficult for the air to flow easily through the airways, and it becomes difficult to breathe.
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Chronic Obstructive Lung Disease (COPD): A chronic inflammatory lung disease results in irreversible airflow obstruction from the lungs. The leading cause of COPD is prolonged cigarette smoking. Other factors that play a role in the development of COPD are genetic disorders such as alpha 1 antitrypsin deficiency and occupational hazards due to long-term exposure to obnoxious chemical fumes, vapors, and dust particles which can inflame the lung parenchyma. The enzyme alpha 1 antitrypsin is produced by the liver and secreted into the bloodstream to protect the lungs. The enzyme helps inhibit the elastase enzyme; therefore, all the elastin is broken down. COPD mainly consists of two disorders: chronic bronchitis and emphysema. These two conditions can co-occur and can vary in severity. Chronic bronchitis is the inflammation of the lining epithelium of the bronchi. Emphysema is a condition in which the alveoli are destroyed due to exposure to irritating gases and cigarette smoking.
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Cystic Fibrosis: It is an autosomal recessive disorder that causes sticky, thick, hyper-viscous mucus to build up in the lungs. This mucus secretion is not removed; the secretions plug up ducts and the airways, leading to difficulty breathing and increasing the risk of infections. It is a defect in the cystic fibrosis transmembrane regulator (CFTR) gene. The CFTR is an epithelial anion channel in the alveolar ducts that facilitates the transfer of chloride and bicarbonate ions along with water to pass through it.
How Is an Arterial Blood Gas Test Carried Out?
The patient is asked to sit upright or lie in a supine position. The blood sample is collected from an artery, usually the radial artery. A small needle is inserted to withdraw a small amount of blood. The blood sample is sent for further investigation. A cotton ball is applied at the puncture site with pressure to stop bleeding or for vasoconstriction.
What Are the Risk Factors Associated with an Arterial Blood Gas Analysis Test?
The risk factors are usually rare. It may include
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Lightheadedness or dizziness.
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Multiple puncture sites to locate the artery.
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Hematoma formation due to rupture of blood vessels and blood pooling under the skin.
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Excessive bleeding.
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Infections at the site of puncture.
Conclusion:
Arterial blood gas analysis is an important diagnostic tool in critically ill patients for diagnosing various life-threatening diseases, including several lung conditions. It also helps determine how well the therapy works in certain lung disorders.
