Which ABG pattern defines metabolic alkalosis?

• A. pH > 7.45 with elevated HCO3-
• B. pH < 7.35 with elevated HCO3-
• C. pH > 7.45 with low PaCO2
• D. pH < 7.35 with low HCO3-

Answer: (A)

Metabolic alkalosis shows an alkaline pH with an elevated bicarbonate level, because the primary disturbance is a metabolic gain of base or loss of hydrogen ions leading to a higher HCO3-. The body may compensate by hypoventilating to raise PaCO2, but the defining feature is high HCO3- with a pH above normal. So the pattern of pH > 7.45 with elevated HCO3- best defines metabolic alkalosis.

If the pattern showed a low pH with high HCO3-, that would not fit metabolic alkalosis. If the pH was high with low PaCO2, that would indicate a respiratory alkalosis. If both pH and bicarbonate were low, that would be metabolic acidosis.