Respiratory system: types of hypoxia: practice question

A Physiology 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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Physiology · Respiratory system: types of hypoxia

Sample item

After cyanide poisoning, a patient has severe tissue hypoxia but a normal PaO2, normal haemoglobin and unusually high mixed venous oxygen saturation. Which type of hypoxia is this?

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

The answer and the reasoning

A. Histotoxic hypoxia

Cyanide inhibits cytochrome oxidase, so tissues cannot use the oxygen delivered. Arterial and venous oxygen contents therefore stay high, and the venous blood is bright red. Hypoxic hypoxia has a low PaO2, anaemic hypoxia has a low oxygen content from low or abnormal haemoglobin, and stagnant hypoxia has low flow.

Option by option

  • A. Histotoxic hypoxia (correct)

    Correct. Cells cannot use oxygen, so venous saturation stays high.

  • B. Hypoxic hypoxia

    Hypoxic hypoxia has a low PaO2, which is normal here.

  • C. Anaemic hypoxia

    Anaemic hypoxia has low haemoglobin, which is normal here.

  • D. Stagnant hypoxia

    Stagnant hypoxia from poor flow produces a large arteriovenous oxygen difference, not a small one.

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 Physiology question

What is the answer to this Physiology question?

The best answer is A, Histotoxic hypoxia. Cyanide inhibits cytochrome oxidase, so tissues cannot use the oxygen delivered.

Why is "Hypoxic hypoxia" not the answer?

Hypoxic hypoxia has a low PaO2, which is normal here.

Why is "Anaemic hypoxia" not the answer?

Anaemic hypoxia has low haemoglobin, which is normal here.

Why is "Stagnant hypoxia" not the answer?

Stagnant hypoxia from poor flow produces a large arteriovenous oxygen difference, not a small one.

What concept does this question test?

It tests Respiratory system: types of hypoxia in Physiology. Arterial and venous oxygen contents therefore stay high, and the venous blood is bright red. Hypoxic hypoxia has a low PaO2, anaemic hypoxia has a low oxygen content from low or abnormal haemoglobin, and stagnant hypoxia has low flow.

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 Respiratory system: types of hypoxia?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.