Critical care: anion gap: practice question

A Anaesthesia 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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Anaesthesia · Critical care: anion gap

Sample item

A patient with severe diarrhoea has pH 7.28, HCO3 14 mEq/L and a normal anion gap. What is the type of acidosis?

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

The answer and the reasoning

D. Normal anion gap (hyperchloraemic) metabolic acidosis

Loss of bicarbonate from the gut is replaced by chloride retention, leaving a normal anion gap of 8 to 12. High-gap acidosis is caused by lactate, ketones, uraemia and toxins.

Option by option

  • A. High anion gap metabolic acidosis

    A high gap implies unmeasured anions.

  • B. Respiratory acidosis

    PaCO2 would be raised in respiratory acidosis.

  • C. Lactic acidosis

    Lactic acidosis raises the gap.

  • D. Normal anion gap (hyperchloraemic) metabolic acidosis (correct)

    Correct. Diarrhoea causes a normal gap acidosis.

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 Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is D, Normal anion gap (hyperchloraemic) metabolic acidosis. Loss of bicarbonate from the gut is replaced by chloride retention, leaving a normal anion gap of 8 to 12.

Why is "High anion gap metabolic acidosis" not the answer?

A high gap implies unmeasured anions.

Why is "Respiratory acidosis" not the answer?

PaCO2 would be raised in respiratory acidosis.

Why is "Lactic acidosis" not the answer?

Lactic acidosis raises the gap.

What concept does this question test?

It tests Critical care: anion gap in Anaesthesia. High-gap acidosis is caused by lactate, ketones, uraemia and toxins.

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 Critical care: anion gap?

Make a table of each agent, its key advantage and its main side effect. Then use the flashcards and the other Anaesthesia 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.