ABG shows pH 7.48, PaCO2 40 mmHg, HCO3- 30 mEq/L. What is the primary disturbance?

ABG shows pH 7.48, PaCO2 40 mmHg, HCO3- 30 mEq/L. What is the primary disturbance?

• A. Respiratory alkalosis
• B. Metabolic acidosis with metabolic compensation
• C. Metabolic alkalosis with respiratory compensation
• D. Normal acid-base status

Answer: (C)

Alkalemia is present (pH 7.48). The primary disturbance is determined by the abnormal component that would drive the pH in the alkaline direction. Here the bicarbonate is elevated (HCO3- 30 mEq/L), pointing to a metabolic alkalosis rather than a primary respiratory problem. In metabolic alkalosis, the body compensates by hypoventilating to raise CO2; this makes PaCO2 increase from its baseline. The PaCO2 of 40 mmHg is within the normal range but lies in the direction of the expected compensatory response (toward higher CO2) and the pH remains alkalemic, which fits metabolic alkalosis with respiratory compensation.

Alkalemia is present (pH 7.48). The primary disturbance is determined by the abnormal component that would drive the pH in the alkaline direction. Here the bicarbonate is elevated (HCO3- 30 mEq/L), pointing to a metabolic alkalosis rather than a primary respiratory problem. In metabolic alkalosis, the body compensates by hypoventilating to raise CO2; this makes PaCO2 increase from its baseline. The PaCO2 of 40 mmHg is within the normal range but lies in the direction of the expected compensatory response (toward higher CO2) and the pH remains alkalemic, which fits metabolic alkalosis with respiratory compensation.