Which ABG pattern indicates metabolic alkalosis due to calcium carbonate ingestion?

• A. pH 7.32, pCO2 48, HCO3 20
• B. pH 7.29, pCO2 54, HCO3 26
• C. pH 7.49, pCO2 40, HCO3 30
• D. pH 7.38, pCO2 52, HCO3 32

Answer: (C)

Metabolic alkalosis presents with a high pH and an elevated bicarbonate level, because there is an excess of base in the blood. Calcium carbonate ingestion adds alkali, raising bicarbonate and driving alkalosis. The pattern with pH 7.49 and HCO3 30 shows an alkalemic state with elevated bicarbonate, which fits this mechanism. The pCO2 is 40, which is within the normal range; some respiratory compensation would raise pCO2, but a normal value can occur if compensation is incomplete or timing is early. The other patterns either show acidemia or a mixed disorder, not the straightforward rise in both pH and bicarbonate seen with this cause.