Regulation Of Serum Potassium

Question 1

What is the normal serum K+ and what happens if it deviates from this? compare this to the intracellular value. How is it excreted and what decreases/ increases its excretion?

Answer 1

3.5-5.5mmol/L But most intracellular (130-140mmol/l)

Too high- nerve dysfunction, cardiac arrest

Too low- nerve dysfunction,cardiac arrest

Insulin decreases serum K+ for 6hrs by putting it into cells and stopping it being excreted

Kidneys excrete 80% of K+, bowels 20%

Need to increase urinary excretion or dialysis to remove K+

Question 2

What’s a healthy amount of K+ to consume per day, what happens if you eat more than this?

Answer 2

1mmol K+ per kg body weight per day

High K+ diet good- reducing BP, CVD, strokes

Question 3

Compare the percentage body weight that is fluid in: adult men, adult woman, infants, elderly

Answer 3

Adult women: 55% 
Men: 60%
Muscle retains more water 
Infants: 75%
Elderly: 50%

Question 4

What can you see on an ECG trace of someone who is hypokalaemic?

Answer 4

Depressed St segment
Diphasic T wave
Prominent U wave

Question 5

Compare the hyperkalaemic ECG trace of someone above 6mmol/l, 7.5,9 and above?

Answer 5

> 6 tall t wave

> 7.5 long PR interval, wide QRS duration, tall T wave

> 9 absent P wave, sinusoidal wave

> > asytole

Question 6

What are some symptoms of hypokalaemia?

Answer 6

Atrial fibrillation, muscle weakness, muscle cramps, constipation

<2.5 Increasing weakness, cardiac conduction abnormalities (APs set off too easily), cardiac arrest

Question 7

Explain what happens to K+ as it gets filtered into and through the nephron?

Answer 7

All filtered through to bowmans capsule

67% reabsorbed at PCT

Some reabsorbed at thin ascending limb LOH passively and in thick part actively

Some moves back into nephron at distal convoluted tubule in Na antiporter from interstitium

Question 8

What does furosemide do and how?

Answer 8

It’s-a diuretic and blocks the Na/K/2Cl channel on LOH

Side effect: hypokalaemia

Question 9

What does spinolactone do and how?

Answer 9

Blocks aldosterone secretion - prevents K+ being moved into nephron from interstitium though K+ H+ symporter

Potassium-sparing diuretic

Can lead to hyperkalaemia

Question 10

State where the following diuretics act on the nephron: acetazolamide, osmotic diuretics (mannitol), loop diuretics (furosemide, thiazides, potassium-sparing

Answer 10

Acetazolamide - PCT 
OD- DL LOH 
LD - aL LOH 
Thiazides (HCTZ) - DCT
Potassium-sparing (spironolactone) - DCT & CD

Question 11

Causes of raised serum potassium

Answer 11

Lack of excretion: 
Acute kidney injury 
Chronic kidney injury 
Potassium sparing diuretics 
ACE- inhibitors 
Aldosterone deficiency 

Release from cells: 
Acidosis (H+ in, K+out)
Cellular breakdown (ischaemia/ toxins) 
Rhabdomyolysis 

XS administration:
K containing fluids or meds
Blood transfusion (stored leaks out)

Question 12

How to treat hyperkalaemia?

Answer 12

Immediate: insulin shifts K into cells lasts 6hrs, salbutamol same as above, calcium stabilised cardiac membrane potential

Later: low K diet, calcium resonium to bind K in gut (can get constipation), stop offending meds’, furosemide, dialysis

Question 13

Causes of hypokalaemia

Answer 13

Insulin/ alkalosis/ beta 2 against- K enters cells

Extra renal losses (diarrhoea/ laxatives)

Decreased intake

Renal losses (diuretics, renal tubular acidosis, diabetic ketoacidosis)

Question 14

Treatment of hypokalaemia

Answer 14

Treat cause

Give K replacement (bananas, oranges, Sando-k)

IV saline +40mmol KcL, dextrose +40 KCL, central concentrated KcL

Potassium sparing diuretics (spironolactone/ Amiloride)