What is metabolic acidosis?

• A. A condition characterized by HCO3 loss or acid accumulation other than carbonic acid
• B. A high pH with elevated bicarbonate
• C. A condition with decreased PaCO2 only
• D. A disease of the liver

Answer: (A)

Metabolic acidosis is about a fall in bicarbonate or an excess of fixed acids that lowers the blood pH. Bicarbonate is the main buffer in blood, so when it’s lost (for example with diarrhea or renal impairment) or when non-carbonic acids (lactic, ketoacids, etc.) accumulate, the hydrogen ion concentration rises and pH drops. In ABG terms, you’d see a low pH and a low HCO3-, with the body trying to compensate by blowing off CO2 (lower PaCO2) through rapid breathing.

The other statements don’t fit because they describe conditions that are not metabolic acidosis: a high pH with elevated bicarbonate points to metabolic alkalosis; a decrease in PaCO2 alone indicates a primary respiratory disturbance; and a liver disease is not the defining feature of metabolic acidosis.