Acid Base Disturbance in Copd 1

Question

Vignette: A 62-year-old man with a history of chronic obstructive pulmonary disease (COPD) presents to the emergency department with worsening dyspnea and cough. His sputum is purulent and he has had a low-grade fever for the past two days. His arterial blood gas reveals a pH of 7.32, PaCO2 of 60 mmHg, and HCO3 of 28 mmol/L. Which of the following is most likely contributing to the patient's acid-base disturbance?

Choices

A. Metabolic acidosis

B. Metabolic alkalosis

C. Respiratory acidosis

D. Respiratory alkalosis

E. Mixed acid-base disorder

Answer

C. Respiratory acidosis

Explanation

The patient's COPD has likely been exacerbated, leading to an inability to adequately ventilate, which is causing a buildup of carbon dioxide (hypercapnia). This leads to a primary respiratory acidosis as evidenced by the elevated PaCO2 and a low pH. The elevated bicarbonate (HCO3) is a compensatory response to this primary respiratory acidosis, as the kidneys attempt to retain bicarbonate in order to buffer the excess hydrogen ions present due to the hypercapnia. This is a classic example of a pathophysiologic response to chronic respiratory disease.