The eyeball approach

You can get a quick idea of your patient's acid-base status in uncomplicated cases by comparing blood gas results to the expected values of pH 7.4, pCO2 = 40 and bicarbonate = 24.
  1. Look at the pH to determine whether the patient is normal, acidotic, or alkalotic.

  2. Look at the PCO2 and bicarbonate to see which of those has the same acid-base deviation as the pH (e.g., if the pH is acidotic, look to see whether the pCO2 is high--which produces acidosis--or the bicarbonate is low--which also produces acidosis). This defines the primary problem. If the pCO2 deviation is in the same acid-base direction as the pH, the problem is respiratory; if the bicarbonate deviation is in the same acid-base direction as the pH, the problem is metabolic.

  3. Look to see whether the other parameter (pCO2 or bicarb) deviates in an acid-base direction opposite the pH. If it does, there is compensation (respiratory if the opposite deviation occurs in the pCO2, metabolic if the compensation occurs in the bicarbonate value).

  4. If both parameters deviate in the acid-base direction of the pH, then there is a mixed acidosis or alkalosis (both systems are contributing to the problem).