Critical care: respiratory compensation in metabolic acidosis: 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: respiratory compensation in metabolic acidosis

Sample item

A patient has a bicarbonate of 12 mmol/L. According to Winter's formula, what PaCO2 is expected with appropriate compensation?

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

The answer and the reasoning

C. About 26 mmHg

Winter's formula gives expected PaCO2 as 1.5 times bicarbonate plus 8, with a range of plus or minus 2. Here it is 1.5 times 12 plus 8, which equals 26 mmHg. A higher measured value indicates a concurrent respiratory acidosis and a lower value a respiratory alkalosis.

Option by option

  • A. About 40 mmHg

    A PaCO2 of 40 would mean no compensation.

  • B. About 12 mmHg

    This is the bicarbonate value and not the formula result.

  • C. About 26 mmHg (correct)

    Correct. 1.5 times 12 plus 8 equals 26 mmHg.

  • D. About 60 mmHg

    A PaCO2 of 60 suggests superimposed respiratory failure.

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 C, About 26 mmHg. Winter's formula gives expected PaCO2 as 1.

Why is "About 40 mmHg" not the answer?

A PaCO2 of 40 would mean no compensation.

Why is "About 12 mmHg" not the answer?

This is the bicarbonate value and not the formula result.

Why is "About 60 mmHg" not the answer?

A PaCO2 of 60 suggests superimposed respiratory failure.

What concept does this question test?

It tests Critical care: respiratory compensation in metabolic acidosis in Anaesthesia. 5 times bicarbonate plus 8, with a range of plus or minus 2. Here it is 1.5 times 12 plus 8, which equals 26 mmHg. A higher measured value indicates a concurrent respiratory acidosis and a lower value a respiratory alkalosis.

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 Critical care: respiratory compensation in metabolic acidosis?

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.