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Lactic Acidosis in Liver Disease — FRCA Final MCQ

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ModerateIntensive Care MedicineLactic Acidosis in Liver DiseaseFRCA Final

A critically ill 55-year-old man with liver cirrhosis is haemodynamically unstable. His arterial blood gas shows pH 7.27, PaCO₂ 3.3 kPa, PaO₂ 12.0 kPa, HCO₃⁻ 11 mmol/L and lactate 8.5 mmol/L. Which option best describes the acid-base disturbance, including the adequacy of compensation?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: B — Primary metabolic acidosis with appropriate respiratory compensation

Explanation lettering: D = shown as A · A = shown as B · B = shown as C · C = shown as D

This is a primary metabolic acidosis with appropriate respiratory compensation (A). The low pH and markedly reduced HCO₃⁻ establish the primary metabolic process, while the raised lactate identifies an important lactic component. Winter's formula predicts a PaCO₂ of (1.5 × 11) + 8 = 24.5 mmHg, equivalent to 3.27 kPa, with an approximate expected range of 3.00–3.53 kPa. The measured PaCO₂ of 3.3 kPa is therefore appropriate compensation. Mixed metabolic and respiratory acidosis (C) would require a PaCO₂ above the expected range. Respiratory acidosis (B) requires an increased PaCO₂. Metabolic alkalosis (D) requires an increased bicarbonate, while primary respiratory alkalosis (E) would not adequately explain the severe bicarbonate reduction and raised lactate.

Reference: Marano M, Jain D, Aggarwal HK, Izzo F. Evaluation of Expected Ventilatory Response to Metabolic Acidosis in Severely Ill Patients. Journal of the Association of Physicians of India. 2021;69(11):11–12. https://pubmed.ncbi.nlm.nih.gov/34781612/