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Metabolic acidosis respiratory compensation — FRCA Primary MCQ

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HardPhysiologyMetabolic acidosis respiratory compensationFRCA Primary

A patient with bowel ischaemia has pH 7.21, PaCO2 3.2 kPa, bicarbonate 10 mmol/L and lactate 8 mmol/L. What is the most likely interpretation?

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Correct answer: C — Metabolic acidosis with respiratory compensation

Low bicarbonate and high lactate indicate metabolic acidosis, while the low PaCO2 reflects compensatory hyperventilation. Primary respiratory alkalosis would not explain the markedly low bicarbonate and high lactate. Respiratory acidosis would have a raised PaCO2. In lactic acidosis, losing respiratory compensation through sedation or fatigue can cause rapid deterioration.

Reference: Ganong Review of Medical Physiology; Primary FRCA physiology texts