Arterial Blood Gas - The importance of pH

Having difficulty interpreting arterial blood gases (ABG)? Perhaps the most important aspect in interpreting ABGs is the pH. If you have ever seen a pool man do his job, then you should be able to interpret ABGs with ease.

A pool man tests the water. What exactly is he testing? He is testing the pH of the water. He is ensuring that it's neither too acidic or alkaline. The water must have a normal pH to ensure the safety of the swimmers.

Likewise, the blood has a normal pH. A perfect adult pH is 7.40. If the pH drops below 7.40, the blood is said to be Acidic. If the pH rises above 7.40, it is said to be alkalitic. If the blood pH is below or above 7.40, it does not necessarily mean that the body is in danger. There is a normal range of the blood pH that is acceptable and safe. The range is 7.35 to 7.45.

So the body can still be acidic and safe (7.35-7.39). Likewise, the body can be alkalotic and safe (7.41-7.45).

What can alter the pH? Well, that's the million dollar question! There are two main organs that add acid and alkaline to the blood.
1. Lungs (Respiratory System)
2. Kidneys (Metabolic System)

The lungs are responsible for exhaling CO2. The lungs add acidity to the blood when the lungs do not properly exhale CO2. Also, the lungs can add alkaline to the blood when the lungs get rid of too much CO2.

How much CO2 should be in the blood? A perfect CO2 would be 40mmHg. Anything above that indicates that the lungs have "added" acidity to the blood. Anything below that indicates that the lungs have "added" alkaline to the blood. A safe range for CO2 is 35-45mmHg.

The kidneys (Metabolic System) are responsible for bicarbonate (HCO3). The kidneys add acidity to the blood when there is a low level of HCO3. Also, the kidneys can add alkaline to the blood when there is a high level of HCO3.

How much HCO3 should be in the blood? A perfect HCO3 is 24mEq/L. Anything above that indicates that the kidneys have "added" alkaline to the blood. Anything below that indicates that the kidneys have "added" acidity to the blood. A safe range for HCO3 is 22-26mEq/L.

Those are just the normal values. To get a good handle on how to interpret ABGs, this tutorial is for you. Click and watch how quickly you learn!
http://www.youtube.com/watch?v=b2dTPBwuiyM