The 6 Easy Steps to ABG Analysis ::: Penolong Pegawai Perubatan

1. Is the pH normal?
2. Is the CO2 normal?
3. Is the HCO3 normal?
4. Match the CO2 or the HCO3 with the pH
5. Does the CO2 or the HCO3 go the opposite direction of the pH?
6. Are the pO2 and the O2 saturation normal?

Step 1: Analyze the pH

The first step in analyzing ABGs is to look at the pH. Normal blood pH is 7.4, plus or minus 0.05, forming the range 7.35 to 7.45. If blood pH falls below 7.35 it is acidic. If blood pH rises above 7.45, it is alkalotic. If it falls into the normal range, label what side of 7.4 it falls on. Lower than 7.4 is normal/acidic, higher than 7.4 is normal/alkalotic. Label it.


Step2: Analyze the CO2

The second step is to examine the pCO2. Normal pCO2 levels are 35-45mmHg. Below 35 is alkalotic, above 45 is acidic. Label it.


Step 3: Analyze the HCO3

The third step is to look at the HCO3 level. A normal HCO3 level is 22-26 mEq/L. If the HCO3 is below 22, the patient is acidotic. If the HCO3 is above 26, the patient is alkalotic. Label it.


Step 4: Match the CO2 or the HCO3 with the pH

Next match either the pCO2 or the HCO3 with the pH to determine the acid-base disorder. For example, if the pH is acidotic, and the CO2 is acidotic, then the acid-base disturbance is being caused by the respiratory system. Therefore, we call it a respiratory acidosis. However, if the pH is alkalotic and the HCO3 is alkalotic, the acid-base disturbance is being caused by the metabolic (or renal) system. Therefore, it will be a metabolic alkalosis.


Step 5: Does the CO2 or HCO3 go the opposite direction of the pH?

Fifth, does either the CO2 or HCO3 go in the opposite direction of the pH? If so, there is compensation by that system. For example, the pH is acidotic, the CO2 is acidotic, and the HCO3 is alkalotic. The CO2 matches the pH making the primary acid-base disorder respiratory acidosis. The HCO3 is opposite of the pH and would be evidence of compensation from the metabolic system.


Step 6: Analyze the pO2 and the O2 saturation.

Finally, evaluate the PaO2 and O2 sat. If they are below normal there is evidence of hypoxemia.