Abstract

An 82 year old woman was admitted with worsening dyspnoea. Arterial blood gases were taken on air and revealed a pH of 7.39, with a partial pressure of CO₂ (pCO₂) of 1.2 kPa, pO₂ of 19.3 kPa, HCO₃ of 13.8 mmol/litre, and base excess of −16.3 mmol/litre: a compensated metabolic acidosis with hyperventilation induced hypocapnia, which is known to be a feature of lactic acidosis. There was also an increased anion gap ((Na140 + K4.0) – (Cl 106 + HCO₃ 13.8)  =  24.2 mEq/litre (reference range, 7–16)), consistent with unmeasured cation. Lactate was measured and found to be raised at 3.33 mmol/litre (reference range, 0.9–1.7). After exclusion of common causes of lactic acidosis Atorvastatin was stopped and her acid–base balance returned to normal. Subsequently, thiamine was also shown to be deficient. The acidosis was thought to have been the result of a mitochondrial defect caused by a deficiency of two cofactors, namely: ubiquinone (as a result of inhibition by statin) and thiamine (as a result of dietary deficiency).