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Question 389
Pathology → General
Classification
Question
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A patient develops acute dyspnoea and pleuritic chest pain following venous thromboembolism. Which combination of arterial blood gas and ventilation-perfusion findings is most consistent with pulmonary embolism?
Question Stem
Select the single best answer.
Options
A
Hyperoxia, hypercarbia and matched loss of ventilation and perfusion
B
Hypoxaemia, hypocarbia, increased alveolar-arterial oxygen gradient and preserved ventilation with absent perfusion
C
Hypoxaemia, hypercarbia, reduced alveolar-arterial oxygen gradient and absent ventilation with preserved perfusion
D
Normal oxygenation with isolated loss of ventilation in the affected region
E
Hyperoxia with preserved perfusion and absent ventilation
Explanation
The classical arterial blood gas findings described for pulmonary embolism are hypoxia, hypocarbia and an increased alveolar-arterial oxygen gradient. A positive ventilation-perfusion scan demonstrates persistent ventilation in the affected region with absent perfusion.
Option Validity
A) Pulmonary embolism classically causes hypoxaemia rather than hyperoxia, and the V/Q defect is mismatched rather than matched.
C) hypocarbia and an increased A-a oxygen gradient, with ventilation preserved and perfusion absent.
D) The characteristic V/Q abnormality is loss of perfusion despite persistent ventilation, and hypoxaemia is expected.
E) This reverses the characteristic ventilation-perfusion relationship and incorrectly specifies hyperoxia.
Further Reading
Saxena R. Textbook for MRCOG-1. Chapter 5: Pathology. General Pathology, pp.161–175.