Session 6: Regulation of Serum Potassium

Question 1

Normal serum K+

Answer 1

3.5 - 5.5 mmol/l

Question 2

Where can most of the K+ be found in the body?

Answer 2

Intracellularly (Around 140 mmol/l)

Question 3

In which foods can you find potassium?

Answer 3

Bananas Avocado Cocoa/chocolate Coconuts Potatoes Tomatoes

Question 4

How much of a male’s total body mass consist of fluid?

Answer 4

Around 60%

Question 5

How much of a female’s total body mass consist of fluid?

Answer 5

Around 55%

Question 6

Why do males consist of more fluid than females?

Answer 6

Because males generally have more muscle. More muscle -> more water

Question 7

Rough fraction of fluid in elderly.

Answer 7

45-50%

Question 8

Rough fraction of fluid in infants

Answer 8

73-75%

Question 9

ECG changes of hyperkalaemia.

Answer 9

Tall T wave Prolonged PR interval Widened QRS duration Absent P wave Sinus wave

Question 10

ECG changes of hypokalaemia.

Answer 10

Depressed ST segment T wave inversion Prominent U wave

Question 11

Complications of hyperkalaemia

Answer 11

Nerve dysfunction, muscle weakness. Ventricular fibrillation, asystole.

Question 12

Complications of hypokalaemia

Answer 12

Atrial fibrillation Muscle weakness Muscle cramps Constipation Cardiac arrest

Question 13

Initial concentration of K+ in ultrafiltrate

Answer 13

3.5 - 5.5 mmol/l

Question 14

Where is potassium reabsorbed in the nephron?

Answer 14

PCT Thick ascending limb of loop of Henle

Question 15

What happens to K+ in the DCT and collecting duct

Answer 15

It can be secreted into the lumen of the tubule again.

Question 16

Where is most of potassium reabsorbed?

Answer 16

In the PCT

Question 17

How much potassium is reabsorbed in the PCT?

Answer 17

Roughly 67%

Question 18

State the names of the drugs acting on each part of the nephron.

1

2

3

4

5

Answer 18

1 - Acetazolamide

2 - Osmotic diuretics like Mannitol

3 - Loop diuretics like furosemide

4 - Thiazides

5 - Spironolactone

Question 19

Causes of raised potassium (Broad)

Answer 19

Lack of excretion

Release from cells

Excess administration

Question 20

Causes of raised potassium due to lack of excretion

Answer 20

Acute kidney injury

Chronic kidney disease

Potassium sparing diuretics like Spironolactone

ACE - inhibitors, ARBS

Aldosterone deficiency

Question 21

Causes of raised potassium due to release from cells.

Answer 21

Acidosis

Cellular breakdown like in ischaemia, toxins, chemo or rhabdomyolysis

Question 22

Give examples of excess K+ administration causing hyperkalaemia.

Answer 22

Potassium containing fluids or medications

Blood transfusions

Question 23

Immediate hyperkalaemia treatment

Answer 23

Insulin to shift K+ into cells. This last for 6 hours

Salbutamol has same action as insulin - 6 hours

Calcium which stabilisis cardiac membrane potential.

Calcium gluconate is a common treatment

Question 24

Long-standing hyperkalaemia treatments

Answer 24

Low K+ diet

Calcium resonium to bind potassium in gut

Stop medications causing raised K+

Furosemide

Dialysis

Question 25

Causes of hypokalaemia

Answer 25

K+ entering cells e.g. insulin, alkalosis or b2 agonists

Extra renal losses in diarrhoea or laxatives

Decreased intake

Rena losses in diuretics, renal tubular acidosis or diabetic ketoacidosis

Question 26

Treatment of hypokalaemia.

Answer 26

Treat the cause like diuretics, diarrhoea, poor oral intake.

Give K+ replacement

Orally - bananas, oranges, sando- K

IV - Saline +40 mmol KCl, Dextrose + 40mmol KCl, Central concentrated KCl

Potassium sparing diuretics like spironolactone or amiloride

Question 27

What metabolic disturbances does extremely low ECF potassium concentrations lead to?

Answer 27

Inability of the kidney to form concentrated urine

Metabolic alkalosis

Enahncement of renal ammonium excretion

Question 28

Where do carbonic anhydrase inhibitors act?

Answer 28

The only class of diuretic drugs that act on the promixal tubule.

Question 29

Carbonic anhydrase inhibitors are not particularly potent.

Why?

What are they used for instead?

Answer 29

They inhibit NaHCO3- reabsorption rather than NaCl reabsorption.

Since there is less HCO3- in the glomerular filtrate there is a reduced effect on Na+ reabsorption.

E.g. Acetazolamide increase excretion of bicarbonate with accompanying Na+, K+ and water. This leads to alkaline urine and metabolic acidosis.

This is no longer used as diuretics but instead for treatment of glaucoma, and also in some unusual types of infantile epilepsy.