MEDizzy - A 58-year-old male is transported to the Emergency

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General Principles (Multisystem Processes)

A 58-year-old male is transported to the Emergency Department for impaired breathing. Arterial blood gases show a pH = 7.35, PaCO2 =60 mm Hg, and [HCO3–] = 31 mEq/L. Which of the following is the most likely differential diagnosis of the patient?

ExplanationThe interpretation of the arterial blood gas is compensated respiratory acidosis. The primary disturbance is an elevation in arterial Pco2 due to alveolar hypoventilation from the impaired mechanics of breathing in COPD. The hypercapnia lowers the ratio of HCO3– to dissolved CO2 in the plasma, and thus lowers the pH according to the Henderson-Hasselbalch equation. To compensate for the acidosis, the kidneys increase the net excretion of H+, which increases the plasma [HCO3–], returning the pH back into the normal range.