General

Question 1

Polydipsia + polyuria, normal BM. Which further investigation would be useful to determine the cause?

Answer 1

calcium

Question 2

Three week history of persistent vomiting. In addition to a severe extracellular fluid volume deficit, what electrolyte disturbance is she likely to have?

Answer 2

Hypocholoraemia, hypokalaemia, metabolic alkalosis.

Diarrhoea can cause a normal anion gap acidosis.

She has been vomiting hydrochloric acid. This will create a metabolic alkalosis from hydrogen ion loss and hypochloraemia from loss of chloride. Hypokalaemia is a consequence of the process: dehydration and sodium loss stimulates the production of aldosterone via the renin-angiotensin-aldosterone system and therefore sodium is reabsorbed at the collecting duct in exchange for potassium, which is lost in the urine.