Electrolyte imbalances

Question 1

How do we calculate an anion gap?

Answer 1

(sodium + potassium) - (bicarbonate + chloride)

A normal anion gap is 8-14 mmol/L

Question 2

Causes of a normal anion gap or hyperchloraemic metabolic acidosis?

Answer 2

gastrointestinal bicarbonate loss: diarrhoea, ureterosigmoidostomy, fistula
renal tubular acidosis
drugs: e.g. acetazolamide
ammonium chloride injection
Addison’s disease

Question 3

Causes of a raised anion gap metabolic acidosis?

Answer 3

lactate: shock, hypoxia
ketones: diabetic ketoacidosis, alcohol
urate: renal failure
acid poisoning: salicylates, methanol
5-oxoproline: chronic paracetamol use