SAQ 434 – Paediatrics – hypoglycaemia with lactic acidosis

Paediatrics – hypoglycaemia with lactic acidosis.

a. Significant abnormalities

• Severe acidaemia with pH 7.10.
• Low bicarbonate at 11 mmol/L.
• Markedly elevated lactate at 8.8 mmol/L.
• Low pCO2 for a venous sample, suggesting respiratory compensation.
• Hypoglycaemia with glucose 1.8 mmol/L.
• Borderline high chloride at 110 mmol/L may contribute to the acidosis.

b. Acid-base disturbance

• Primary metabolic acidosis.
• Anion gap = Na – (Cl + HCO3) = 143 – (110 + 11) = 22 mmol/L, so there is an increased anion gap component.
• Lactate of 8.8 mmol/L explains much of the high anion gap metabolic acidosis.
• Expected pCO2 by Winter's formula is about 1.5 x 11 + 8 = 24.5 mmHg, plus or minus 2. The measured venous pCO2 is 37 mmHg, so compensation is less than expected and a concurrent respiratory acidosis or inadequate ventilatory compensation is possible.
• Hypoglycaemia is a separate critical abnormality requiring immediate treatment.

c. Differential diagnoses

• Hypoglycaemic seizure with secondary lactic acidosis.
• Sepsis or shock/hypoperfusion, although the absence of fever makes this less straightforward.
• Toxic ingestion, especially a combination such as sulfonylurea plus metformin, noting no single common ingestion perfectly explains the picture.
• Inborn error of metabolism or disorder of gluconeogenesis.
• Mitochondrial respiratory chain disorder.
• The original examiner noted this differential is clinically controversial and internally difficult to explain from the provided stem.