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MBBS QUESTION #10254
Question 1
A patient presents with hypoxemia and hypercapnia on arterial blood gas (Type II respiratory failure), for example due to opioid overdose or severe COPD exacerbation. The primary underlying mechanism is most often:
  • Alveolar hypoventilation, reducing overall gas exchange for both O2 and CO2✔️
  • A pure diffusion defect with entirely normal minute ventilation
  • An isolated right-to-left cardiac shunt with normal ventilation
  • Ventilation-perfusion mismatch with normal total alveolar ventilation
Correct Answer Explanation
CO2 retention specifically reflects inadequate alveolar ventilation relative to metabolic CO2 production (since CO2 diffuses easily and is very sensitive to ventilation), distinguishing Type II failure (hypoxemia + hypercapnia, hypoventilation-driven) from Type I failure (hypoxemia alone, typically from V/Q mismatch or shunt with normal or low CO2).