Which statement describes the hallmarks of metabolic acidosis?

Which statement describes the hallmarks of metabolic acidosis?

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

Answer: (C)

Metabolic acidosis shows a metabolic component driving the acidemia: bicarbonate (HCO3-) is low, which pulls the pH down. The body responds quickly by breathing faster to blow off CO2, so the PaCO2 falls as a compensatory mechanism. So the hallmark pattern is low HCO3-, low pH, and a reduced PaCO2 due to respiratory compensation. The statement that matches this is the one with low bicarbonate and low pH, with compensatory low PaCO2. The other descriptions describe alkalosis or a normal state, or reflect a primary respiratory alkalosis pattern, and don’t fit metabolic acidosis.

Metabolic acidosis shows a metabolic component driving the acidemia: bicarbonate (HCO3-) is low, which pulls the pH down. The body responds quickly by breathing faster to blow off CO2, so the PaCO2 falls as a compensatory mechanism. So the hallmark pattern is low HCO3-, low pH, and a reduced PaCO2 due to respiratory compensation.

The statement that matches this is the one with low bicarbonate and low pH, with compensatory low PaCO2. The other descriptions describe alkalosis or a normal state, or reflect a primary respiratory alkalosis pattern, and don’t fit metabolic acidosis.