Paediatric emergencies: methaemoglobinaemia: 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 · Paediatric emergencies: methaemoglobinaemia

Sample item

A 2-year-old develops cyanosis after drinking water from a well with high nitrate content. SpO2 is 85 percent and does not improve with oxygen, PaO2 is normal and blood drawn is chocolate brown. Which antidote is indicated?

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

The answer and the reasoning

B. Methylene blue

Methaemoglobinaemia occurs when iron in haemoglobin is oxidised to the ferric state by nitrates, nitrites, aniline dyes or drugs, so it cannot carry oxygen. Cyanosis with a normal PaO2, unresponsive to oxygen, and chocolate-coloured blood suggest it. Methylene blue reduces methaemoglobin to haemoglobin, and is avoided in G6PD deficiency.

Option by option

  • A. Physostigmine

    Physostigmine reverses anticholinergic toxicity.

  • B. Methylene blue (correct)

    Correct. Methylene blue restores iron to the ferrous state through NADPH-dependent reduction.

  • C. N-acetylcysteine

    N-acetylcysteine is the antidote for paracetamol overdose.

  • D. Hydroxocobalamin

    Hydroxocobalamin is an antidote for cyanide poisoning.

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 B, Methylene blue. Methaemoglobinaemia occurs when iron in haemoglobin is oxidised to the ferric state by nitrates, nitrites, aniline dyes or drugs, so it cannot carry oxygen.

Why is "Physostigmine" not the answer?

Physostigmine reverses anticholinergic toxicity.

Why is "N-acetylcysteine" not the answer?

N-acetylcysteine is the antidote for paracetamol overdose.

Why is "Hydroxocobalamin" not the answer?

Hydroxocobalamin is an antidote for cyanide poisoning.

What concept does this question test?

It tests Paediatric emergencies: methaemoglobinaemia in Pediatrics. Cyanosis with a normal PaO2, unresponsive to oxygen, and chocolate-coloured blood suggest it. Methylene blue reduces methaemoglobin to haemoglobin, and is avoided in G6PD deficiency.

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 Paediatric emergencies: methaemoglobinaemia?

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.