Interpret the following ABG values: pH 7.26, PaCO2 55 mm Hg, PaO2 68 mm Hg, HCO3- 24 mEq/L. Which disorder is indicated?

• A. Metabolic acidosis
• B. Metabolic alkalosis
• C. Respiratory acidosis
• D. Respiratory alkalosis

Answer: (C)

When interpreting ABG values, start with the pH to see if there is acidemia or alkalemia. A pH of 7.26 shows acidemia. Next, look at the PaCO2 to identify the primary cause. A PaCO2 of 55 mm Hg is elevated, indicating CO2 retention and a respiratory origin. The bicarbonate is 24 mEq/L, which is normal, suggesting there is little to no metabolic compensation at this moment. In respiratory acidosis, the elevated CO2 lowers the pH, and compensation (an increase in HCO3-) develops over time; the lack of increased bicarbonate points to an acute process rather than a chronic one. So the pattern fits respiratory acidosis, likely acute. The PaO2 of 68 mm Hg shows some hypoxemia, which can accompany respiratory issues but doesn’t change the diagnosis of the primary acid-base disturbance.