Normal Values:
pH = 7.36 - 7. 44 (7.40)
PCO2 = 36 - 44 mmHg (40 mmHg)
HCO3 = 22 - 26 mEq / L (24 mEq / L)
AG = Na - (Cl + HCO3) (Normal AG = 12 ± 2)

Approach: Compare the pH and the PCO2 values. If the pH and PaCO2 are both abnormal, compare the directional change. If both change in the same direction (both increase or decrease), the primary acid-base disorder is metabolic, and if both change in opposite directions, the primary acid-base disorder is respiratory.