Renal and acid–base: salicylate poisoning: 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 · Renal and acid–base: salicylate poisoning

Sample item

A 24-year-old woman who took a large number of aspirin tablets has tinnitus, rapid deep breathing and sweating. Arterial blood shows pH 7.46, PaCO2 20 mmHg and bicarbonate 14 mmol/L with a raised anion gap. Which description is correct?

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

The answer and the reasoning

A. Primary respiratory alkalosis together with an anion gap metabolic acidosis

Salicylates stimulate the respiratory centre directly, causing a primary respiratory alkalosis, and they uncouple oxidative phosphorylation and cause accumulation of organic acids, producing a high anion gap metabolic acidosis. The pH is therefore near normal or alkaline, which a pure compensated acidosis would not give.

Option by option

  • A. Primary respiratory alkalosis together with an anion gap metabolic acidosis (correct)

    Correct. A direct respiratory stimulation and a high anion gap acidosis coexist.

  • B. Pure respiratory alkalosis with renal compensation

    A raised anion gap and a bicarbonate of 14 are too great to be explained by renal compensation alone, and the compensation takes days.

  • C. Metabolic alkalosis with respiratory compensation

    A low bicarbonate and low PaCO2 rule out metabolic alkalosis.

  • D. Pure anion gap metabolic acidosis with respiratory compensation

    In a compensated metabolic acidosis the pH remains acidic and does not become alkaline.

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, Primary respiratory alkalosis together with an anion gap metabolic acidosis. Salicylates stimulate the respiratory centre directly, causing a primary respiratory alkalosis, and they uncouple oxidative phosphorylation and cause accumulation of organic acids, producing a high anion gap metabolic acidosis.

Why is "Pure respiratory alkalosis with renal compensation" not the answer?

A raised anion gap and a bicarbonate of 14 are too great to be explained by renal compensation alone, and the compensation takes days.

Why is "Metabolic alkalosis with respiratory compensation" not the answer?

A low bicarbonate and low PaCO2 rule out metabolic alkalosis.

Why is "Pure anion gap metabolic acidosis with respiratory compensation" not the answer?

In a compensated metabolic acidosis the pH remains acidic and does not become alkaline.

What concept does this question test?

It tests Renal and acid–base: salicylate poisoning in Physiology. The pH is therefore near normal or alkaline, which a pure compensated acidosis would not give.

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 Renal and acid–base: salicylate poisoning?

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.