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Monday, December 14, 2015

ABGs: What patients need to know

The following was originally published at on June 29, 2015

What is an Arterial Blood Gas

So you have COPD, and now your doctor wants you to have an Arterial Blood Gas (ABG). So what is an ABG, and how do the results benefit you?

An ABG is a special blood draw that requires arterial blood, or freshly oxygenated blood from your lungs. The test shows your oxygen levels, which show how effective your lungs are at oxygenating, or taking the gas oxygen (O2) from the air you inhale and getting it into your bloodstream.

These include.
  • PaO2. This is the partial pressure of arterial oxygen. Normal is 80-100, although greater than 60 is usually acceptable. 
  • SaO2. This is how saturated your arterial blood is with oxygen (O2). Normal is 98%, although 90-100 is deemed acceptable. Sometimes 88-92 is acceptable for COPD. 
All the cells and tissues of your body, such as those that make up your heart, need oxygen to make the energy needed for them to function. Lacking enough oxygen, your heart may stop working properly and make you feel winded or short of breath. So monitoring your oxygen levels from time to time when you have a disease like COPD is important.

If your oxygen levels are low, your doctor may prescribe oxygen therapy to help you breathe easier and live longer with your lung disease.

The test also shows how effective your lungs are at ventilating, or taking the gas carbon dioxide (CO2) from your blood and allowing you to get rid of it when you exhale.

This is shown as.
  • PaCO2. This is the partial pressure of arterial carbon dioxide (CO2). The normal range is 35-45.
An elevated PaCO2 level may indicate how severe your flare-up is, how much your disease has progressed, or even what stage of COPD you are in. It can help doctors decide how best to treat your flare-up. It can also help doctors decide how your treatment regime is working over time and whether adjustments need to be made.

The results also show.
  • HCO3 (Bicarbonate). This is a buffer that keeps your pH from getting too acidic. A normal range is 22-26. 
  • pH. This measures hydrogen ions (H+) in your blood. A normal value is 7.35 to 7.45. Your PaCO2 and HCO3 are constantly adjusted by your body to maintain a normal pH.
So an ABG requires arterial blood. The best place to draw it is from the radial artery in your wrist. The second best place is the brachial artery on the anterior side of your elbow.

An advantage of drawing blood from an artery is that arteries are deeper and less likely to roll than veins, plus they pulsate, which sometimes makes arterial blood easier to obtain. A disadvantage is arteries are surrounded by more nerves than veins, sometimes making arterial pokes more uncomfortable than venous pokes.

As an asthmatic, I’ve had the test performed on me more than once, and I can honestly say it’s really not that bad. As a respiratory therapist who has been drawing them for 20 years, I can honestly say that most people tolerate the poke just fine.

The test is also not performed very often, because most laboratory tests require only venous blood. Still, for the occasional times doctors recommend for you to have this test done, the results can go a long way to helping them help you live better with it.

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