Neonatology: hyperoxia test: practice question

A Pediatrics 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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Pediatrics · Neonatology: hyperoxia test

Sample item

A cyanosed newborn is given 100 percent oxygen for 10 minutes, but the arterial PaO2 stays low, below about 100 mmHg. What does this indicate?

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

The answer and the reasoning

C. Cyanotic congenital heart disease with a fixed right-to-left shunt

In the hyperoxia test, a rise of PaO2 above about 150 mmHg on 100 percent oxygen suggests lung disease, since ventilated alveoli can raise it. A failure to rise points to a fixed intracardiac right-to-left shunt, so echocardiography is the next step.

Option by option

  • A. Hypoventilation from central nervous system depression

    Hypoventilation improves with oxygen and ventilation, raising PaO2.

  • B. Methaemoglobinaemia

    Methaemoglobinaemia gives a normal PaO2, since the defect lies in the haemoglobin.

  • C. Cyanotic congenital heart disease with a fixed right-to-left shunt (correct)

    Correct. Shunted blood bypasses the lungs and so oxygen does not raise PaO2.

  • D. Parenchymal lung disease such as pneumonia

    Lung disease usually shows a clear rise in PaO2 with supplemental oxygen.

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 Pediatrics question

What is the answer to this Pediatrics question?

The best answer is C, Cyanotic congenital heart disease with a fixed right-to-left shunt. In the hyperoxia test, a rise of PaO2 above about 150 mmHg on 100 percent oxygen suggests lung disease, since ventilated alveoli can raise it.

Why is "Hypoventilation from central nervous system depression" not the answer?

Hypoventilation improves with oxygen and ventilation, raising PaO2.

Why is "Methaemoglobinaemia" not the answer?

Methaemoglobinaemia gives a normal PaO2, since the defect lies in the haemoglobin.

Why is "Parenchymal lung disease such as pneumonia" not the answer?

Lung disease usually shows a clear rise in PaO2 with supplemental oxygen.

What concept does this question test?

It tests Neonatology: hyperoxia test in Pediatrics. A failure to rise points to a fixed intracardiac right-to-left shunt, so echocardiography is the next step.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Neonatology: hyperoxia test?

Memorise milestones and the vaccine schedule as tables and revise them often. Then use the flashcards and the other Pediatrics 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.