ABG: pH 7.28, PaCO2 60, HCO3- 26. What is the primary disorder?

• A. Metabolic acidosis
• B. Acute respiratory acidosis
• C. Chronic respiratory acidosis
• D. Metabolic alkalosis

Answer: (B)

This question tests interpreting acid-base status and distinguishing acute versus chronic respiratory disturbances. The low pH shows an acidemia. The elevated PaCO2 indicates carbon dioxide retention is driving the acidosis, pointing to a respiratory origin. The bicarbonate is 26, which is within the normal range and only modestly elevated, matching what we expect in acute, not chronic, respiratory acidosis. In acute respiratory acidosis, the body hasn’t had time to fully compensate, so bicarbonate rises by only about 1 mEq/L for each 10 mmHg increase in PaCO2; a 20 mmHg rise from 40 to 60 would typically yield a bicarbonate around 26, as seen here. If it were chronic respiratory acidosis, renal compensation would raise bicarbonate more substantially (often into the 30s). Metabolic disorders would disrupt the bicarbonate in a way that wouldn’t align with the CO2-driven acidemia.

So the primary disorder is acute respiratory acidosis.