In a patient with cirrhosis and hyperventilation, which acid-base disorder is most likely?

• A. Anion gap metabolic acidosis
• B. Metabolic alkalosis
• C. Respiratory alkalosis
• D. Non-anion gap metabolic acidosis

Answer: (C)

Hyperventilation drives CO2 loss, which shifts the carbonic acid–bicarbonate balance toward bicarbonate decrease and raises blood pH. The primary disturbance here is respiratory alkalosis from blowing off CO2, and in cirrhosis this can occur with hepatic encephalopathy or other causes of hyperventilation. The kidneys may compensate by excreting some bicarbonate, so HCO3− can drop a bit, but the key finding is a high pH with low PaCO2, characteristic of respiratory alkalosis.

This differs from metabolic acidoses (anion gap or non-anion gap), which lower pH and involve decreases in bicarbonate from nonrespiratory processes, and from metabolic alkalosis, which raises pH due to increased bicarbonate or H+ loss. Respiratory acidosis would come from hypoventilation with elevated PaCO2, not from hyperventilation.