Conn’s syndrome

In primary hyperaldosteronism (Conn’s syndrome) which one of the following is

MOST LIKELY to be found on routine blood investigations?

a) High potassium, low sodium and high hydrogen ions

b) High potassium, low sodium and low hydrogen ions

c) Low potassium, low sodium and high hydrogen ions

d) Low potassium, high sodium and high hydrogen ions

e) Low potassium, high sodium and low hydrogen ions

Answer: e

Explanation

Conditions such as Conn’s syndrome are loved by examiners, as they are a

pathology that makes the candidate think clearly about normal physiology. In

clinical practice they are rarely seen by anaesthetists, but this piece of information

is of little solace sitting in the exam room. It is also a condition much loved by

physicians, as it is one of the few causes of hypertension that you can do something

about.

Aldosterone maintains circulating volume by retaining sodium. An excess of aldosterone

will lead to an excess of renal re-absorption of sodium in exchange for potassium.

There then may be increased secretion of hydrogen ions in the collecting duct in

response to the hypokalaemia. In the real world of clinical medicine, patients with

Conn’s syndrome do present with hypokalaemia and alkalosis, but rarely have

hypernatraemia.