Which value must be assessed to determine if a metabolic disturbance is present?

• A. HCO3
• B. PaO2
• C. SaO2
• D. Lactate

Answer: (A)

In acid-base balance, the metabolic component is reflected by bicarbonate. HCO3- is the primary metabolic buffer in the blood, and the kidneys adjust its level to compensate for metabolic acid loads. When a metabolic disturbance is present, HCO3- shifts away from normal: a low bicarbonate indicates metabolic acidosis, while a high bicarbonate indicates metabolic alkalosis. PaO2 and SaO2 relate to oxygenation and don’t tell you about metabolic acid-base problems. Lactate can rise in certain metabolic states like lactic acidosis, but it’s a secondary marker rather than the primary test to identify a metabolic disturbance. Therefore, the value that must be assessed to determine a metabolic disturbance is the bicarbonate concentration.