Urinary11 - Regulation of Serum Potassium

Question 1

Normal Potassium Values

Serum Potassium
Intracellular Potassium
Urine Potassium

Answer 1

1. ) Serum (Extracelullar) Potassium - 3.5-5.5 mmol/L
2. ) Intracellular Potassium - 140 mM
3. ) Urine Potassium - 60-80 mM, can be > 130 mM

Question 2

Movement of potassium ions in the kidney nephron

PCT
Thick Ascending Limb
DCT
Collecting Duct

Answer 2

1. ) PCT - K+ reabsorption (67%)
   - paracellular diffusion driven by lumen positive charge
2. ) Thick Ascending Limb - K+ reabsorption (20%)
   - using NKCC2 and K-Cl symporter
3. ) DCT - small K+ reabsorption
   - K-Cl symporter
4. ) Collecting Duct - variable K+ excretion
   - principle cells contain ENaC channels which are regulated by aldosterone (RAAS) (inhibited by amiloride)
   - Na+ exchanged for K+ ions, K+ excreted using ROMK

Question 3

3 groups of causes of hyperkalaemia

Reduced Excretion x6
Increased Release x2
Excess Administration x2

Answer 3

1. ) Reduced Excretion of K+ - caused by:
   - acute kidney injury (AKI) chronic kidney disease (CKD)
   - K+ sparing diuretics (spironolactone), ACEi, ARBs
   - aldosterone deficiency (Addison’s Disease)
2. ) Increased Release from Cells - caused by:
   - acidosis, cellular breakdown (ischaemia, toxins, chemo, rhabdomyolysis)
3. ) Excess Administration
   - potassium containing fluid or medication
   - blood transfusion

Question 4

3 characteristic features of hyperkalemia on an ECG

> 6.0 mM
7.5 mM
9.0 mM

Answer 4

1. ) >6.0 mM - tall T waves
2. ) >7.5 mM - wide QRS complex, prolonged PR interval
3. ) >9.0 mM - absent p wave, sinusoidal wave

Question 5

Treatments for hyperkalaemia

Immediate Treatments x3
Longer Term Treatments x4

Answer 5

1. ) Immediate Treatments - lasts 4-6 hours
   - IV calcium gluconate 10% 30ml or IV calcium chloride 10% 10ml given over 5-10 mins (stabilises the heart)
   - IV actrapid 10 units with IV glucose 25g
   - NEB salbutamol 5mg (4x back to back)
2. ) Longer Term Treatments
   - dietary: low potassium diet, calcium resonium to bind potassium in gut
   - loop diuretics: furosemide to enhance potassium loss in urine
   - dialysis

Question 6

4 groups of causes for hypokalaemia

Diet
Cell Entry
GI
Urine

Answer 6

1. ) Reduced Dietary Intake
2. ) Increased Cell Entry - metabolic alkalosis, increase in B-adrenergic acitivity (e.g. NA during stress)
3. ) Increased GI Loss - vomiting, diarrhoea
4. ) Increased Urine Loss - increase in urine flow, renal tubular acidosis, magnesium deficiency, SIADH
   - increase in aldosterone: volume depletion, primary and secondary hyperaldosteronism
   - loop or thiazide diuretic: volume depletion and increase in urine flow

Question 7

Symptoms of hypokalemia

2.5-3 mM
<2.5 mM

Answer 7

1. ) 2.5-3 mM - atrial fibrillation, muscles weakness, muscle cramps, constipation
2. ) <2.5 mM - cardiac conduction abnormalities, cardiac arrest

Question 8

2 types of treatment for hypokalaemia

Answer 8

1.) Treat Underlying Cause

2. ) Potassium Replacement - oral, IV, or diuretics
   - oral: bananas, oranges, sando-K
   - IV: saline + 40mM KCl, dextrose + 40mM KCl
   - K+ sparing diuretics: spironolactone, amiloride