Respiratory medicine: acute severe asthma: practice question

A General Medicine question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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General Medicine · Respiratory medicine: acute severe asthma

Sample item

A 24-year-old asthmatic woman is brought in with severe breathlessness. She can speak only single words, her heart rate is 130 per minute and her peak flow is 30% of her best. Arterial blood gas on supplemental oxygen shows PaO2 70 mmHg, PaCO2 44 mmHg and pH 7.36. How should the PaCO2 be interpreted?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Ominous, because a normal PaCO2 in severe asthma signals tiring and impending respiratory failure

In acute asthma the intense respiratory drive causes hyperventilation, so PaCO2 is normally low. A normal or rising PaCO2 means the patient can no longer sustain the work of breathing and is a life-threatening feature, as are silent chest, cyanosis, exhaustion and confusion. Such patients need senior and intensive care review.

Option by option

  • A. Reassuring, because the value lies within the normal range

    The value is only normal in numbers; it is abnormal for a patient who should be hyperventilating.

  • B. Evidence of chronic carbon dioxide retention from COPD overlap

    A 24-year-old with asthma has no basis for chronic retention, and the picture is acute.

  • C. Ominous, because a normal PaCO2 in severe asthma signals tiring and impending respiratory failure (correct)

    Correct. A normal PaCO2 in this setting indicates ventilatory failure is approaching.

  • D. An effect of oxygen therapy, which lowers carbon dioxide

    Oxygen corrects hypoxaemia but does not lower PaCO2; high-flow oxygen can in fact raise it in at-risk patients.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this General Medicine question

What is the answer to this General Medicine question?

The best answer is C, Ominous, because a normal PaCO2 in severe asthma signals tiring and impending respiratory failure. In acute asthma the intense respiratory drive causes hyperventilation, so PaCO2 is normally low.

Why is "Reassuring, because the value lies within the normal range" not the answer?

The value is only normal in numbers; it is abnormal for a patient who should be hyperventilating.

Why is "Evidence of chronic carbon dioxide retention from COPD overlap" not the answer?

A 24-year-old with asthma has no basis for chronic retention, and the picture is acute.

Why is "An effect of oxygen therapy, which lowers carbon dioxide" not the answer?

Oxygen corrects hypoxaemia but does not lower PaCO2; high-flow oxygen can in fact raise it in at-risk patients.

What concept does this question test?

It tests Respiratory medicine: acute severe asthma in General Medicine. A normal or rising PaCO2 means the patient can no longer sustain the work of breathing and is a life-threatening feature, as are silent chest, cyanosis, exhaustion and confusion. Such patients need senior and intensive care review.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Respiratory medicine: acute severe asthma?

For each disease know the classic presentation, the best test, and the first-line treatment. Then use the flashcards and the other General Medicine questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.