Potassium and Electrolytes

Question 1

What is the normal range of potassium?

Answer 1

3.5-5.0 mmol/L

Question 2

Which hormones are involved in regulation of potassium?

Answer 2

Angiotensin 2

Aldosterone

Question 3

What does aldosterone stimulate?

Answer 3

Sodium reabsorption and potassium excretion

Question 4

What is the mechanism by which aldosterone increases sodium reabsorption?

Answer 4

Reduced degradation of sodium channels

Question 5

What are the main stimuli for aldosterone secretion?

Answer 5

Angiotensin 2

Rise in potassium

Question 6

Why will kidney failure (reduced GFR) cause hyperkalaemia?

Answer 6

Because the kidneys secrete renin, which will convert angiotensinogen to angiotensin 1

Question 7

Under what circumstances is there reduced activity of renin?

Answer 7

Type 4 renal tubular acidosis (diabetic nephropathy)

NSAIDs

Question 8

What drugs can cause hyperkalaemia?

Answer 8

ACE inhibitors
Angiotensin receptor blockers
Aldosterone antagonists
(Also NSAIDs but via a different mechanism)

Question 9

What conditions can cause hyperkalaemia?

Answer 9

Addison's disease
Rhabdomyolysis
Acidosis (when H+ goes into cells - to try and reduce the acidosis - potassium goes out)

Question 10

How is hyperkalaemia managed?

Answer 10

Get an ECG

10 mL 10% calcium gluconate or chloride
Combined glucose + insulin = 50 mL 50% dextrose + 10 units of insulin
Nebulised salbutamol

Treat underlying cause

Question 11

Which drug used in management does not actually fix the hyperkalaemia but protects the heart?

Answer 11

10 mL 10% calcium gluconate

Question 12

What are causes of hypokalaemia?

Answer 12

GI loss
Renal loss = hyperaldosteronism, Cushings’ syndrome, increased excretion of sodium, osmotic diuresis
Redistribution into cells = insulin, beta agonists, alkalosis
Rare causes = renal tubular acidosis types 1 and 2, hypomagnesaemia

Question 13

What is the triple transporter?

Answer 13

Transporter in the ascending loop of Henle that reabsorbs sodium, potassium, and chloride

Question 14

What conditions block the triple transporter?

Answer 14

Loop diuretics
Bartter syndrome (genetic mutation in the transporter)

Question 15

What happens if/when the triple transporter is blocked?

Answer 15

More sodium reaches the distal nephron and thus is reabsorbed, making the nephron more negative
Thus more potassium is lost down the electrochemical gradient

Question 16

What drugs/conditions cause more sodium to be delivered to the distal nephron?

Answer 16

Thiazide diuretic
Gitelman syndrome (mutation in Na/Cl channel)

Question 17

What are clinical features of hypokalaemia?

Answer 17

Muscle weakness
Cardiac arrhythmia
Polyuria and polydipsia

Question 18

What screening test would be ordered in a patient with hypokalaemia and hypertension?

Answer 18

Aldosterone : renin ratio

In primary hyperaldosteroneism, you would expect this to be high because high aldosterone would suppress renin.

Question 19

How is hypokalaemia managed?

Answer 19

3.0-3.5 mmol/L = oral potassium chloride (2x SandoK tablets for 48 hours)
<3.0 mmol/L = IV potassium chloride

Treat underlying cause