Respiratory physiology and ventilation: curriculum recognition: 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 · Respiratory physiology and ventilation: curriculum recognition

Sample item

In recovery, a drowsy patient with no prior lung disease who received a large dose of opioid has pH 7.22, PaCO2 68 mmHg and bicarbonate 26 mmol/L. Which acid-base disorder is present?

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

The answer and the reasoning

C. Acute respiratory acidosis

A high PaCO2 with a low pH and almost normal bicarbonate shows an acute rise in CO2 before the kidneys have compensated. In chronic hypercapnia the bicarbonate rises considerably and the pH is nearer to normal. Treatment is to restore ventilation.

Option by option

  • A. Chronic respiratory acidosis with renal compensation

    Chronic retention would show a markedly raised bicarbonate and a less acidic pH.

  • B. Mixed respiratory and metabolic alkalosis

    Alkalosis would show a raised pH, not a pH of 7.22.

  • C. Acute respiratory acidosis (correct)

    Correct. Raised PaCO2 and low pH with near-normal bicarbonate indicates an acute process.

  • D. Metabolic acidosis with respiratory compensation

    In metabolic acidosis the bicarbonate is low and the PaCO2 is low.

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, Acute respiratory acidosis. A high PaCO2 with a low pH and almost normal bicarbonate shows an acute rise in CO2 before the kidneys have compensated.

Why is "Chronic respiratory acidosis with renal compensation" not the answer?

Chronic retention would show a markedly raised bicarbonate and a less acidic pH.

Why is "Mixed respiratory and metabolic alkalosis" not the answer?

Alkalosis would show a raised pH, not a pH of 7.22.

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

In metabolic acidosis the bicarbonate is low and the PaCO2 is low.

What concept does this question test?

It tests Respiratory physiology and ventilation: curriculum recognition in Anaesthesia. In chronic hypercapnia the bicarbonate rises considerably and the pH is nearer to normal. Treatment is to restore ventilation.

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 physiology and ventilation: curriculum recognition?

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.