Acid-base physiology: 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 · Acid-base physiology

Sample item

A patient has pH 7.28, bicarbonate 14 mmol/L, and low PaCO2 from hyperventilation. What primary acid-base disorder is present?

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

The answer and the reasoning

C. Metabolic acidosis with respiratory compensation

Low pH and low bicarbonate identify metabolic acidosis, while reduced PaCO2 represents respiratory compensation through hyperventilation. The anion gap and clinical context then guide diagnosis.

Option by option

  • A. Respiratory acidosis with renal compensation

    Respiratory acidosis would have elevated PaCO2.

  • B. Metabolic alkalosis

    Metabolic alkalosis has elevated bicarbonate.

  • C. Metabolic acidosis with respiratory compensation (correct)

    Correct. Bicarbonate reduction is primary and ventilation compensates.

  • D. Respiratory alkalosis only

    Respiratory alkalosis alone would not explain the low bicarbonate and acidemia.

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 C, Metabolic acidosis with respiratory compensation. Low pH and low bicarbonate identify metabolic acidosis, while reduced PaCO2 represents respiratory compensation through hyperventilation.

Why is "Respiratory acidosis with renal compensation" not the answer?

Respiratory acidosis would have elevated PaCO2.

Why is "Metabolic alkalosis" not the answer?

Metabolic alkalosis has elevated bicarbonate.

Why is "Respiratory alkalosis only" not the answer?

Respiratory alkalosis alone would not explain the low bicarbonate and acidemia.

What concept does this question test?

It tests Acid-base physiology in Physiology. The anion gap and clinical context then guide diagnosis.

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 Acid-base physiology?

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.