Arterial blood gas

Arterial blood gas

Now and then, my doctor asks that I have an arterial blood gas analysis. What exactly is this? Also, I would like to better understand what is meant by PCO2.

To understand what an arterial blood gas analysis is, you must first know what an artery is. The circulatory system includes the following:

1) Arteries that carry blood that has been freshly oxygenated by the lungs, from the heart to peripheral
tissues;
2) Capillaries, which are tiny blood vessels where gases and nutrients are exchanged with the tissues;
3) Veins that carry blood from the peripheral tissues back to the heart.

Most blood samples are taken from veins. Some are taken by pricking the fingertip, where capillary blood is obtained. However, when accurate information on lung function is needed, it is preferable to collect blood that has just come from the heart-lung unit. The sample is usually taken by puncturing the radial artery, which is located on the inside of the wrist at the base of the thumb, just beneath the skin. A local anesthetic may be necessary. Because blood pressure in this vessel is much higher than in a vein, pressure must be applied to the artery after the blood is collected to prevent bleeding.

An arterial blood gas sample is used to analyze blood acidity (pH) and the pressure of oxygen (PO2) and carbon dioxide (PCO2). We all know that oxygen is the body’s “fuel” and carbon dioxide is one of the body’s waste products. The lungs’ main function is to supply oxygen to the blood and eliminate carbon dioxide. Blood acidity (pH) and CO2 levels (PCO2) can be measured quite accurately with capillary gas (taken from the fingertip), but the pressure of blood oxygen (PO2) reading is not as reliable. Moreover, in cases of severe lung disease where gas readings are necessary to determine whether oxygen therapy is needed (and if so, how much), an arterial blood gas sample is required.

A device known as the pulse oximeter that is now readily available in clinics and on the market. A small clip attached to an optical system is usually placed on the fingertip; the oxygen level in the blood can be indirectly measured quite accurately without piercing the skin. Although arterial blood gas tests have not been completely eliminated, this device has made it possible to reduce them greatly!

N.B.:   Normal PO2 levels are between 80 and 100. Normal PCO2 levels are between 38 and 42

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