If your blood acid level is out of balance, it can mean your body isn't able to get rid carbon dioxide efficiently. This may happen because your lungs aren't working well or your kidneys can't get rid of the acid. A normal result is between 7. The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand.
Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore.
How far you live above sea level can affect your results. Your blood oxygen goes down as your elevation goes up.
Smoking, inhaling secondhand smoke, having a fever, or breathing quickly can also affect the test results. You don't need to do anything to prepare for the test. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. Search Encyclopedia. Why do I need this test? Here are some of the more common reasons an ABG is ordered: You're often short of breath. You're unusually tired. These hydrogen ions are buffered by combine with bicarbonate to form carbonic acid, which dissociates to carbon dioxide CO 2 and water.
The CO 2 diffuses from blood to alveoli. The process is continuously regulated so that the amount of CO 2 being removed from blood at the lungs equals the amount of CO 2 being added to the blood in the tissues.
This simple relationship, which is central to an understanding of all essential aspects of acid-base balance and interpretation of patient ABG results, states that pH of arterial blood is a function of both p CO 2 a and bicarbonate concentration. The relationship also reveals that pH remains unchanged if both bicarbonate and p CO 2 a are increased or decreased by the same relative amount.
The inverse relationship between pH and p CO 2 a reflects the acidic potential of carbon dioxide remember that when dissolved in blood, carbon dioxide is hydrated to carbonic acid, which dissociates yielding hydrogen ions, see equation above. As already discussed, the process of pulmonary gas exchange in the lungs ensures that p CO 2 a remains constant and in so doing ensures a vital contribution to the maintenance of normal pH.
Clearly if through disease or injury the lungs were unable to eliminate carbon dioxide efficiently, p CO 2 a would rise and pH would fall. Bicarbonate concentration, the nominator in the above equation is dependent on normal kidney function. As the principal buffer in blood, bicarbonate prevents the rapid change in pH that would otherwise occur, when in the normal course of cell metabolism, metabolic acids are released to blood.
As bicarbonate is consumed in this process, it is of itself a very short-term solution to the problem of maintaining the pH of blood to which acids are being added. For continuing effectiveness, bicarbonate must be continuously re-generated and the hydrogen ions they are buffering must be removed from the body.
These two tasks are the work of the kidneys. By adjusting the excretion of hydrogen ions and bicarbonate in urine, and thereby the reabsorption of bicarbonate to blood, the kidneys maintain blood concentration of bicarbonate within normal limits.
This in turn is essential to the maintenance of normal blood pH. The respiratory and renal systems outlined above operate together in maintaining blood pH. Since preservation of blood pH within the normal range is paramount, the normal response to a fall in bicarbonate is a compensatory adjustment downwards of p CO 2 a.
Remember, it is the ratio of bicarbonate: p CO 2 a that must be preserved, if pH is to be maintained within the normal range. Actual bicarbonate is the actual concentration in the sample - uncorrected for p CO 2 a.
May contain information that is not supported by performance and intended use claims of Radiometer's products. See also Legal info. A three-part introduction for the novice - Part 1. Printed from acutecaretesting. January Why measure blood gases? Summary Arterial blood gas ABG analysis generates a number of parameters listed in BOX 5 that together allow assessment of pulmonary gas exchange, blood oxygenation and acid-base balance.
By contrast, arterial blood, which flows in arteries from the heart back to the microvasculature of tissues, is rich in oxygen said to be oxygenated and relatively depleted of carbon dioxide due to the pulmonary gas exchange that occurs when venous blood is diverted from the heart to the lungs via the pulmonary artery , before return to the heart via the pulmonary vein , and then onward journey, via the aorta and arterial system, to the tissues.
The millions of alveoli and their network of tiny blood capillaries provide a massive membrane surface area for gas exchange: around 80 sq. On one side of the alveolar-capillary membrane is alveolar air essentially inspired air ; on the other is venous blood.
The membrane is very thin of the order 0. The direction and rate of this diffusion is governed by the amount or partial pressure of each gas on either side of the membrane. Gases diffuse from areas of high partial pressure to areas of low partial pressure. Box 1: A note on partial presdsure p Maintenance of two measured ABG parameters, p O 2 a and p CO 2 a within normal limits implies effective pulmonary gas exchange, which is dependent on: Adequate alveolar ventilation.
This is the movement of air in and out of alveoli due to the mechanical process of breathing that depends on the chest musculature and elastic recoil of the lungs. Normal numbers of functioning alveoli. Normal thickness of alveolar-capillary membrane.
Sufficient blood flow through pulmonary capillaries i. Intact brain stem explained below. This is only useful if you are receiving oxygen therapy from a tank or are on a ventilator. Many conditions can change blood gas levels.
Your doctor will talk with you about any abnormal results that may be related to your symptoms and past health. Reasons you may not be able to have the test or why the results may not be helpful include the following:. Russo MD - Internal Medicine. Author: Healthwise Staff. Medical Review: E. This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information.
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Top of the page. Test Overview An arterial blood gas ABG test measures the acidity pH and the levels of oxygen and carbon dioxide in the blood from an artery. This measures the pressure of oxygen dissolved in the blood and how well oxygen is able to move from the airspace of the lungs into the blood. Partial pressure of carbon dioxide PaCO2.
This measures the pressure of carbon dioxide dissolved in the blood and how well carbon dioxide is able to move out of the body. The pH of blood is usually between 7. A pH of less than 7. So blood is slightly basic. Bicarbonate HCO3. Bicarbonate is a chemical buffer that keeps the pH of blood from becoming too acidic or too basic. O2 content measures the amount of oxygen in the blood. Oxygen saturation measures how much of the hemoglobin in the red blood cells is carrying oxygen O2.
See how well treatment for lung diseases is working. Find out if you need extra oxygen or help with breathing mechanical ventilation. Your doctor will tell you if you should stop taking any of them before the test and how soon to do it.
Do not smoke just before the test or breathe secondhand smoke. How It Is Done If you are on oxygen therapy, the oxygen may be turned off for 20 minutes before the blood test. How It Feels Collecting blood from an artery is more painful than collecting it from a vein. You may feel lightheaded, faint, dizzy, or nauseated while the blood is being taken from your artery.
Most people feel a brief, sharp pain as the needle to collect the blood sample enters the artery. If you get a local anesthetic, you may feel nothing at all from the needle puncture. Or you may feel a brief sting or pinch as the needle goes through the skin. You may feel more pain if the person drawing your blood has a hard time finding your artery, if your artery is narrowed, or if you are very sensitive to pain.
Risks There is little chance of a problem from having a blood sample taken from an artery. You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for at least 10 minutes after the needle is removed longer if you have bleeding problems or take blood thinners.
In rare cases, the needle may damage a nerve or the artery. This can cause the artery to become blocked. Results Normal Each lab has a different range for what's normal. Results are usually available right away. Credits Current as of: October 26, Previous Section: Related Information Top of the page.
Current as of: October 26,
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