SAQ 303 – Metabolic – non-anion gap metabolic acidosis with hypokalaemia

Metabolic – non-anion gap metabolic acidosis with hypokalaemia.

a. VBG interpretation

• Acidaemia: pH 7.19.
• Metabolic acidosis: bicarbonate 15 mmol/L.
• Appropriate respiratory compensation: pCO2 30 mmHg; expected pCO2 is about 31.
• Anion gap is approximately 14; delta ratio supports isolated non-anion gap metabolic acidosis.
• Hypokalaemia is marked, especially relative to the degree of acidaemia.
• Summary: isolated normal-anion-gap metabolic acidosis with clinically important hypokalaemia.

b. Likely contributors

• Hyperchloraemia from saline administration.
• Diarrhoeal bicarbonate loss.

c. Other causes of NAGMA

• Renal tubular acidosis.
• Mild to moderate renal insufficiency.
• Adrenal insufficiency.
• Drugs such as acetazolamide or spironolactone.
• Gastrointestinal fistula or other bicarbonate loss.

d. Correction

• Prioritise potassium replacement, and consider magnesium replacement, before bicarbonate correction.
• Use isotonic bicarbonate replacement if needed, such as 150 mmol sodium bicarbonate in 850 mL 5% dextrose.