What is the normal range for blood gases?
Blood gas analysis measures the levels of oxygen, carbon dioxide, and bicarbonate in the blood as well as the pH level and oxygen saturation. The normal range for blood gases is shown in the table.
Blood gas analysis, also called arterial blood gas analysis (ABG analysis), helps measure
- The concentration of oxygen and carbon dioxide gases in the blood (measured in terms of partial pressure).
- The pH of the blood, revealing how acidic or alkaline the blood is.
- The levels of bicarbonate ions in the blood.
- The oxygen saturation or SaO2 that tells what percentage of hemoglobin (the pigment in the red blood cells) is saturated with oxygen.
ABG analysis is a popular procedure. It can also be done at the patient’s bedside. The test involves a rapid analysis of the parameters. Thus, it is an important tool used by doctors to plan and modify the treatment of their patients. It may be especially useful for a patient who is critically ill such as those with heart diseases, kidney diseases or uncontrolled diabetes. The test can reveal whether the exchange of gases is occurring properly in the body. This can reflect any abnormalities in the lungs, heart, kidneys or metabolism.
The normal values for various parameters measured through ABG analysis are as followsParameterValuePartial pressure of oxygen (PaO2)75-100 mmHg*Partial pressure of carbon dioxide (PaCO2)38-42 mmHg*pH of arterial blood7.38-7.42Oxygen saturation (SaO2)94-100%Bicarbonate concentration (HCO3)22-28 mEq/L*
*mmHg means millimeters of mercury
**mEq/L stands for milliequivalents per liter
These values represent the ABG analysis done at the sea levels. The values may differ with a change in altitude. There may also be variations in the readings obtained from two different laboratories. Therefore, clinical correlation is necessary.
Why is a blood gas analysis done?
The blood carries dissolved gases such as oxygen and carbon dioxide. Oxygen is added to the blood when it travels through the lungs, whereas the waste gas from the tissues (carbon dioxide) is removed from the blood. The balance of these gases also influences the pH of the blood. Thus, arterial blood gas (ABG) analysis may be performed to diagnose various health conditions that may affect the lungs, heart and kidneys. These medical conditions may manifest as a change in the oxygen saturation, carbon dioxide levels or pH of the blood.
ABG analysis can be used for diagnosing
- Diseases of the lungs such as asthma, chronic obstructive pulmonary disease (COPD) and cystic fibrosis.
- Kidney failure.
- Diabetes complications such as diabetic ketoacidosis (DKA) and hyperglycemic hyperosmolar state (HHS).
- Severe infections or septicemia.
- Drug overdose.
- Heart failure.
Arterial blood sampling may also be done to see the patient’s response to the treatment. It also tells the doctor whether the patient needs supplemental oxygen or other support for breathing.
How is a blood gas analysis performed?
The arterial blood gas (ABG) analysis is a quick procedure that can be done in the outpatient department or by the patient’s bedside (point-of-care test). The patient does not need to prepare for this test.
During the test
The healthcare professional will clean the site from where the blood will be drawn with an antiseptic solution.
Generally, the blood is withdrawn from an artery. The blood is generally withdrawn from the wrist (radial artery), although the groin (femoral artery) or arm (brachial artery) arteries may also be used.
After the antiseptic solution has dried, the professional will insert a small needle through the skin into the artery. The patient may feel a pinching sensation as the needle is introduced into the skin. The professional may use a numbing medicine before introducing the needle to minimize discomfort.
Generally, 1 mL of the blood is withdrawn.
After withdrawing the blood, pressure is applied to the site for a few minutes to stop the bleeding.
The sample will be quickly sent to the laboratory for analysis.