ABG interpretation: pH 7.46; pCO2 50; HCO3- 32. Which pattern best fits this result?

ABG interpretation: pH 7.46; pCO2 50; HCO3- 32. Which pattern best fits this result?

• A. Compensated nonrespiratory alkalosis
• B. Compensated respiratory alkalosis
• C. Uncompensated respiratory alkalosis
• D. Uncompensated nonrespiratory alkalosis

Answer: (A)

The main idea is to identify the primary acid-base disorder and whether there is appropriate compensation. The pH is alkaline (7.46), so we’re dealing with alkalosis. The bicarbonate is elevated at 32 mEq/L, pointing to a metabolic (nonrespiratory) origin. If the primary problem were respiratory alkalosis, the pCO2 would be low, and the kidneys would compensate by lowering bicarbonate, which we don’t see here. Instead, the respiratory system has lowered ventilation enough to raise the CO2 to 50 mmHg as a compensatory response to the metabolic alkalosis. That combination—alkalemia with high bicarbonate and a high, but compensatory, pCO2—fits metabolic alkalosis with respiratory compensation.

The main idea is to identify the primary acid-base disorder and whether there is appropriate compensation. The pH is alkaline (7.46), so we’re dealing with alkalosis. The bicarbonate is elevated at 32 mEq/L, pointing to a metabolic (nonrespiratory) origin. If the primary problem were respiratory alkalosis, the pCO2 would be low, and the kidneys would compensate by lowering bicarbonate, which we don’t see here. Instead, the respiratory system has lowered ventilation enough to raise the CO2 to 50 mmHg as a compensatory response to the metabolic alkalosis. That combination—alkalemia with high bicarbonate and a high, but compensatory, pCO2—fits metabolic alkalosis with respiratory compensation.