Which ABG pattern is expected in metabolic acidosis?

Which ABG pattern is expected in metabolic acidosis?

• A. Low pH and low HCO3
• B. High pH and high HCO3
• C. Normal pH with normal HCO3
• D. Low pH and high HCO3

Answer: (A)

Metabolic acidosis occurs when bicarbonate (HCO3−) falls due to increased acid or bicarbonate loss, so the blood becomes more acidic. The body responds by increasing ventilation to blow off CO2, which helps compensate. On an ABG, this primary change is a low pH with a low HCO3−. The accompanying CO2 may be low as part of that respiratory compensation, but the defining abnormality is the combination of acidemia and reduced bicarbonate.

Patterns with high bicarbonate would point to metabolic alkalosis, a normal pH and normal bicarbonate suggest no primary disorder or a well-compensated/ mixed situation, and a low pH with high bicarbonate would imply a mixed disorder rather than isolated metabolic acidosis.