Hyperkalaemia

Question 1

Define hyperkalaemia

Answer 1

Hyperkalaemia = when serum potassium is greater than 5mmol/L

Question 2

What are the causes and risk factors

Answer 2

1. ) Ingesting too much potassium: usually iatrogenic
2. ) Acute kidney injury: decreased filtration rate so more K+ is maintained in the blood
3. ) Drugs:
   - ACE inhibitors: block binding of aldosterone to receptor
   - Spironolactone: potassium sparing diuretic
   - NSAIDS
   - Ciclosporin
   - Heparin
4. ) Adrenal insuffiency: low levels of aldosterone in kidneys
   - Aldosterone stimulates secretion of K+

Question 3

Describe the epidemiology of hyperkalaemia

Answer 3

• 1.57% in overall population have this

- 6.35% of patients with CKD and or heart failure

Question 4

Describe the pathology of hyperkalaemia

Answer 4

• Remember that the amount of potassium in the blood will determine excitability of nerve and muscle cells
• When K+ levels rise: will reduce difference in electrical potential between cardiac myocytes and the outside of cells. This means the threshold for action potential decreases, so you get abnormal action potential which leads to arrhythmias and cardiac arrest

Question 5

Describe the signs and symptoms of hyperkalaemia

Answer 5

Main symptoms:

• Normally asymptomatic until K+ levels high enough to cause cardiac arrest
• Muscle weakness
• Impaired neuromuscular transmission
• Flaccid paralysis
• Chest pain
• Light headedness

Signs:

1. ) Metabolic acidosis causing Kussmaul’s respiration: a low, deep sighing inspiration and expiration
2. ) Tachycardia

Question 6

Describe the investigations and diagnosis of hyperkalaemia

Answer 6

1. ) ECG:
   - Tall tented T wave
   - Small P wave
   - Wide QRS complex

U&E’s:

• Over 5.5mmol/L = hyperkalaemia
• Over 6.5mmol/L = medical emergency

Question 7

Describe the treatment of hyperkalaemia

Answer 7

If mild:

• treat underlying cause
• dietary potassium restriction
• restriction of drugs causing hyperkalaemia
• loop diuretics e.g. furosemide: increase urinary K+ excretion

If severe:

• Calcium gluconate: decreases VF risk in the heart + protects myocardium by reducing the excitability of cardiac myocytes
• Insulin and dextrose: drives K+ into the cells
• Polystyrene sulphonate resin: binds K+ in the gut to decrease uptake