Low potassium handling - Amir Sam

Question 1

Broad causes of hypokalemia

Answer 1

GI loss
Renal loss
Redistribution of potassium into cells

Question 2

Renal causes of hypokalemia

Answer 2

Increased delivery of sodium to the distal tubule, causing more sodium absorption and potassium excretion.

At the ASCENDING LOOP OF HENLE, this can be caused by:
- Loop diuretics
- Bartter’s syndrome

At the DISTAL COLLECTING DUCT, this can be caused by:
- Thiazide diuretics
- Gitelman syndrome

Question 3

Explain how loop diuretics cause hypOkalemia. Where do loop diuretics work? Which transporters are present there?

Answer 3

Loop diuretics work at the ascending loop of henle, where there are sodium potassium chloride transporters.

Blocking these transporters means more sodium gets transported distally, leading to more sodium being reabsorbed, causing a more negative lumen and thus more potassium being excreted via an electrochemical gradient.

Question 4

Which transporters are present in the ascending loop of Henle?

Answer 4

Na+ K+ Cl- transporters

Question 5

What is Bartter’s syndrome?

Answer 5

Autosomal recessive condition where there is a genetic defect in the sodium potassium chloride transporter of the ascending loop of Henle.

Question 6

Explain which transporters thiazide diuretics act on.

Answer 6

Sodium chloride transporter at distal tubule - also causes downstream increase in sodium reabsorption, and therefore downstream increase in potassium excretion .

Question 7

What is Gitelman syndrome?

Answer 7

An autosomal recessive condition which presents in late childhood, where there is a defect in the sodium chloride transporter in the distal tubule, as well as a defect in the magnesium transporter.

Question 8

How does osmotic diuresis cause hypokalemia?

Answer 8

Hyperglycemia - more peeing - more potassium excreted

Question 9

Give two forms of hyperaldosteronism that cause hypokalemia

Answer 9

Cushings - too much cortisol can work on mineralocorticoid receptors
Conns

Question 10

How does ‘redistribution into cells’ cause hypokalemia? What scenarios bring this on?

Answer 10

Alkalosis can cause hypokalemia. Cells try to compensate for the high blood pH by releasing hydrogen ions in return for potassium. This causes more intracellular potassium and thus hypokalemia.

Other scenarios: high insulin, beta agonists

Question 11

State three rare causes of hypokalemia

Answer 11

Hypomagnesemia
Renal tubular acidosis type 1 and 2

Question 12

What is meant by GI loss of potassium?

Answer 12

Vomiting

Question 13

What are the clinical features of hypokalemia?

Answer 13

Muscle weakness
Cardiac arrhythmia
Polyuria
Polydipsia

Question 14

What screening test would you do if a patient had hypokalemia and hypertension

Answer 14

Check aldosterone to renin ratio

Question 15

What is mild hypokalemia defined as?

Answer 15

3.0-3.5mmol/L

Question 16

How do you treat mild hypokalemia?

Answer 16

Oral potassium chloride - 2x SandoX tablets, three times a day (TDS) for 48 hours

Then recheck serum potassium

Question 17

How do you define very low potassium?

Answer 17

Below 3.0mmol/L

Question 18

How do you treat severe hypokalemia? At what rate is it given?

Answer 18

IV potassium chloride, at a rate of 10mmol/per hour

Treat underlying cause

Question 19

Why should you not give potassium chloride at a rate higher? What is this upper limit?

Answer 19

At a rate higher that 20 mmol/hour, potassium chloride is highly irritating to the peripheral veins.