Acid-Base Balance and ABG Practice Test 2026 – Complete Exam Prep

Metabolic disturbances primarily alter the bicarbonate level (HCO3-) in ABG. In metabolic acidosis, HCO3- decreases as acids accumulate or bicarbonate is lost; in metabolic alkalosis, HCO3- increases from excess base. The pH reflects the balance between HCO3- and PaCO2, so it can be abnormal, but the defining abnormality signaling a metabolic problem is the bicarbonate concentration. PaCO2 shows the respiratory response and tends to compensate for the metabolic change (through hypoventilation or hyperventilation), but it isn’t the primary abnormality of a metabolic disorder. PaO2 concerns oxygenation and is often normal in isolated metabolic disturbances. So, the bicarbonate level is the ABG component typically abnormal in metabolic disturbances.