Exam Guide
Interpreting an ABG in a COPD Exacerbation
Respiratory · Question from the ATI RN Medical-Surgical 2023 Proctored Exam study set
Correct answer: B. Respiratory Acidosis
Why this is the answer
A pH below 7.35 confirms acidosis, and an elevated pCO2 points to a respiratory cause — the lungs are retaining CO2, which is exactly what happens when COPD impairs gas exchange. Metabolic Acidosis (A) is ruled out because a metabolic problem would show a low bicarbonate driving the pH down, not an elevated pCO2. Metabolic Alkalosis (C) is wrong on two counts — the pH here is low, not high, and the disturbance is respiratory, not metabolic. Respiratory Alkalosis (D) would require a low pCO2 (from hyperventilation) paired with a high pH — the opposite of what's shown here.
The bigger concept
The quick rule for classifying an ABG: check the pH direction first (acidic vs alkalotic), then check whether pCO2 or HCO3 is driving it — an abnormal pCO2 points to a respiratory cause, an abnormal HCO3 points to a metabolic one. COPD is the textbook cause of chronic respiratory acidosis from CO2 retention.
Related Respiratory practice questions
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