Which acid-base disturbance is present with pH 7.26 and PaCO2 68 mm Hg in a ventilated patient?

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

Answer: (A)

When the pH is low (acidemia) and the PaCO2 is high, the pattern points to respiratory acidosis. Carbon dioxide acts as an acid in the blood; if ventilation is insufficient, CO2 builds up, forming more carbonic acid and lowering the pH. In a ventilated patient, a PaCO2 of 68 mm Hg means CO2 retention is driving the acidemia, so the primary disturbance is respiratory in origin. Compensation by the kidneys (retaining or excreting bicarbonate) would take time and would shift the bicarbonate level upward, but the current pH and CO2 pattern clearly reflect a respiratory problem. The other scenarios don’t fit: metabolic disturbances would primarily involve changes in bicarbonate with CO2 changes that don’t match the observed acidemia with elevated CO2, and respiratory alkalosis would require a low CO2 with a high pH, which isn’t the case here.