Which statement describes the hallmarks of metabolic alkalosis?

• A. Low HCO3, low pH; compensation: Low PaCO2.
• B. Normal HCO3, normal pH.
• C. High PaCO2, low pH; compensation: High HCO3.
• D. High HCO3, High pH; compensation: High PaCO2.

Answer: (D)

Metabolic alkalosis occurs when there is too much bicarbonate or a loss of hydrogen ions, so the primary change is an elevated HCO3- that pushes the pH upward. The body tries to compensate by retaining carbon dioxide, which raises the PaCO2 through slower, shallower breathing. So the hallmark pattern is high bicarbonate with high pH, plus a compensatory increase in PaCO2.

Common situations producing this are loss of hydrogen ions (like vomiting or losses from diuretics) or ingestion of bicarbonate. The other patterns don’t fit because they describe metabolic acidosis or respiratory issues: low bicarbonate with low pH is metabolic acidosis; normal values imply no disturbance; high PaCO2 with low pH is respiratory acidosis; a combination of high bicarbonate with high pH and high PaCO2 matches metabolic alkalosis with respiratory compensation.