Start your ABG Interpretation with these easy steps:
- Is the pH normal?
- Is CO2 normal?
- Is the HCO3 normal?
- Match the CO2 or the HCO3 with the pH
- Does the CO2 or the HCO3 go the opposite direction of the pH?
- Are the pO2 and the O2 saturation normal?
In order for our ABG interpretation to be effective, notes will have to be written next to the results on our lab slip. Alternately, the ABG results can be transcribed onto another paper for analysis.
- The first step in ABG interpretation 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.
- The second step is to examine the pCO2. Normal pCO2 levels are 35-45mmHg. Below 35 is alkalotic, above 45 is acidic. Label it.
- The third step in our ABG interpretation 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.
- 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.
- 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 the opposite of the pH and would be evidence of compensation from the metabolic system.
- Finally, evaluate the PaO2 and O2 sat. If they are below normal there is evidence of hypoxemia.
Normal Arterial Values (At sea level): Range:
| pH | 7.35-7.45 |
| pCO2 | 35-45 mmHg |
| pO2 | 80-100 mmHg |
| O2 Saturation | 95-100% |
| HCO3- | 22-26 mEq/L |
| Base Excess | + or – 2 |
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