Potassium

Question 1

K+ control by RAA

Answer 1

Low Na or low GFR stimulates renin secretion from JAA
Renin converts angiotensinogen to Angiotensin I
ACE converts Angiotensin I to Angiotensin II
Angiotensin II stimulates adrenals to produce aldosterone
Aldosterone acts on principal cells of CT to suck sodium (reabsorption) and kick out potassium (excretion)
[High K+ will also stimulate adrenal glands]

Question 2

Effect of H+ on K+

Answer 2

H+ and K+ are in antiport in the kidney
In ACIDOSIS need to excrete H+ so less K+ excreted
In ALKALOSIS need to conserve H+ so more K+ excreted
Hence you can get hyperkalaemia in metabolic acidosis

Question 3

Hyperkalaemia causes

Answer 3

3 main causes:

1. Disrupted RAA axis (reduced GFR in AKI
2. Excess intake (rare - usually stored blood sample or excess iv fluid)
3. Shift of K+ out of cells (MA, rhabdomyolysis, tissue damage, DKA)

Question 4

ECG changes in hyperkalaemia

Answer 4

Occur ~6.5 (already too high)
Tall-tented T waves
Loss of P waves
Broad QRS complex
Bradycardia

Question 5

Tx of hyperkalaemia

Answer 5

10ml 10% calcium gluconate (stabilise myocardium)
10IU insulin + 100ml 20% dextrose (drives K+ into cells + protect against hypoglycaemia
Nebulised salbutamol

Question 6

K+ kidney absorption / excretion locations

Answer 6

Absorption - ascending limb via Na / K / Cl co-transporter

Excretion - principal cells in CD

Question 7

Hypokalaemia causes

Answer 7

GI losses
Renal losses (too much aldosterone, loop / Bartter’s (block co-transporter absorption), thiazide / Gitelman’s (block Na aborption = increase Na for exchange in CD)
Sucked into cells (insulin, B-agonists)
Renal Tubular Acidosis (failure to acidify urine)
Hypomagnesemia (rare cause)

Question 8

Conn’s

Answer 8

Too much aldosterone

High Na, low K

Question 9

Addison’s

Answer 9

Adrenal failure = not enough aldosterone

Low Na, high K

Question 10

Tx hypokalaemia (MILD, SEVERE)

Answer 10

Mild (3-3.5) - Oral KCL (SandoK)

Severe (<3) - IV KCL (max 10mmol/L into central vein)

Question 11

Reduced H+ excretion, severe hyperkalaemia

Reduced HCO3- absorption, mild hyperkalaemia

Answer 11

Renal Tubular Acidosis 1

Renal Tubular Acidosis 2

Question 12

Effect of acidosis on K+

Answer 12

Hyperkalaemia

Question 13

Newborn baby

Hypokalaemia, metabolic alkalosis, hypotension

Answer 13

Bartter’s syndrome

Defect in thick ascending loop of Henle prevents potassium reabsorption

Question 14

Why can metabolic alkalosis occur in hypokalaemia?

Answer 14

Low potassium in blood means less potassium is excreted

Therefore less H+ reabsorbed by antiporter in kidney