Chempath - Potassium

Question 1

Potassium normal range

Answer 1

3.5-5.0mmol/L

Question 2

Action of aldosterone

Answer 2

Na+ absorption and K+ excretion

Aldosterone increases number of open Na+ channels in the luminal membrane –> increased sodium reabsorption –>
makes the lumen electronegative & creates an electrical gradient –> potassium is secreted into the lumen

Question 3

Aldosterone secretion from the kidney increased by

Answer 3

Angiotensin 2

Increased potassium

Question 4

Sodium-Potassium exchange

Answer 4

In the principal cells of the cortical collecting tubule. Na reabsorption through ENaC (epithelial sodium channels) leads to tubular lumen negative electrical potential, driving potassium secretion (to balance charges).

Question 5

Main Causes of Hyperkalaemia - Decreased Excretion

Answer 5

Reduced GFR - acute/chronic renal failure

Reduced renin - type 4 renal tubular acidosis, diabetic nephropathy, chronic NSAID use

Reduced ACE - ACE inhibitors

Reduced action of angiotensin II - angiotensin II receptor blocker

Adrenal issues - Addison’s

Reduced action of aldosterone - aldosterone antagonists (K+ sparing diuretics - spironolactone, amiloride)

Question 6

Main Causes of Hyperkalaemia - General

Answer 6

Excessive intake
Transcellular movement  (ICF --> ECF)
Decreased excretion (renin-angiotensin system based)

Renal impairment: reduced renal excretion
Drugs: ACE inhibitors, ARBs, spironolactone
Low Aldosterone - Addison’s disease, Type 4 renal tubular acidosis (low renin, low aldosterone)
Release from cells: rhabdomyloysis, acidosis

Question 7

Main Causes of Hyperkalaemia - Transcellular Movement

Answer 7

Acidosis - H+/K+ exchange to maintain electroneutrality

Rhabdo - K+ leaking from dying cells

Question 8

Hyperkalaemia - ECG changes

Answer 8

Bradycardia
Flattened p waves
Peaked/tall tented Ts waves
Prolonged PR interval

Question 9

Hyperkalaemia - Rx

Answer 9

10 ml 10% calcium gluconate
50 ml 50% dextrose + 10 units of insulin
Nebulized salbutamol (beta agonists can drive potassium intracellularly)
Treat the underlying cause

Question 10

Causes of Hypokalaemia

Answer 10

GI loss - D more so than V

Renal loss- HYPERALDOSTERISM (Conns, BAH), excess cortisol, increased sodium in distal nephron (–> increased aldosterone), osmotic diuresis

Redistribution into cells - insulin, beta agonists (e.g. salbutamol), metabolic alkalosis (H+/K+ exchange)

Rare causes - renal tubular acidosis types 1 and 2, hypomagnesaemia

Question 11

Causes of increased sodium delivery to the distal nephron –> increased K+ exchange

Answer 11

Blockage of triple transporter in ascending limb - thiazide diuretics/gitelman

Blockage of Na+Cl- symporter in distal convoluted tubule - loop diuretics/bartter syndrome)

Question 12

Hypokalaemia - Clinical Features

Answer 12

Muscle Weakness
Cardiac arrhythmia
Polyuria & polydipsia (nephrogenic DI)

Question 13

Screening test for pt with hypokalaemia and hypertension

Answer 13

Aldosterone: Renin ratio

Question 14

Hypokalaemia - Rx

Answer 14

Serum potassium 3.0-3.5 mmol/L:
Oral potassium chloride (two SandoK tablets tds for 48 hrs)
Recheck serum potassium

Serum potassium < 3.0 mmol/L:
IV potassium chloride
Maximum rate 10 mmol per hour
Rates > 20 mmol per hour are highly irritating to peripheral veins

Treat the underlying cause e.g. spironolactone