Potassium Flashcards
What is the normal reference range (NR) for potassium and its primary role? (2)
Potassium is the main intracellular cation.
NR = 3.5–5.5 mmol/L.
What does hypokalaemia always cause, and why? (2)
Always causes metabolic alkalosis.
When potassium is low in the blood, cells compensate by moving potassium out of cells and into the bloodstream.
To maintain electrical neutrality, hydrogen ions (H⁺) move into cells.
This reduces the number of free hydrogen ions in the blood, increasing pH and causing alkalosis.
What categories can causes of hypokalaemia be split into? (4)
GI loss
Renal loss
Redistribution
Rare causes
What are the GI causes of hypokalaemia? (3
Diarrhoea
Vomiting
Fistula
What are the renal causes of hypokalaemia? (6)
Conn’s syndrome
Cushing’s syndrome
Loop diuretics
Thiazide diuretics
Osmotic diuresis
Bartter or Gitelman syndrome
How does Cushing’s syndrome cause renal hypokalaemia? (1)
Ectopic ACTH stimulates mineralocorticoid receptors (MRs), leading to severe hypokalaemia.
How do loop and thiazide diuretics cause hypokalaemia? (2)
Loop diuretics: Block the triple transporter in the ascending loop of Henle (Bartter syndrome mutation).
Thiazide diuretics: Block the Na+-Cl− transporter in the distal convoluted tubule (Gitelman syndrome mutation).
What are the redistribution causes of hypokalaemia? (3)
Insulin
Alkalosis
Beta-agonists (e.g., Salbutamol)
What are the rare causes of hypokalaemia? (2)
Renal tubular acidosis (RTA) Types 1 & 2
Hypomagnesaemia
What is paradoxical aciduria in hypokalaemia? (1)
H+ is lost in urine as a physiological response where the kidney retains K+ in exchange for H+.
How does hypokalaemia present clinically? (2)
Muscle weakness
Arrhythmias (e.g., ventricular fibrillation)
What are the ECG changes in hypokalaemia? (3)
Flattened T waves
U waves
ST depression
What is the management of hypokalaemia based on potassium levels? (2)
K+ 3–3.5 mmol/L:
Oral potassium chloride for 48 hours and recheck levels.
K+ <3 mmol/L:
IV potassium chloride.
What are the types of renal tubular acidosis (RTA), and their key features?
Type 1 (distal RTA):
Most severe.
Distal failure of H+ excretion.
Associated with acidosis and hypokalaemia.
Type 2 (proximal RTA):
Milder.
Proximal failure to reabsorb HCO3−.
Associated with acidosis and hypokalaemia.
Type 4 RTA:
Aldosterone deficiency/resistance.
Associated with acidosis and hyperkalaemia.
What happens in type 1 renal tubular acidosis?
Type 1 (distal RTA):
Most severe.
Distal failure of H+ excretion.
Associated with acidosis and hypokalaemia.
What happens in type 2 renal tubular acidosis?
Type 2 (proximal RTA):
Milder.
Proximal failure to reabsorb HCO3−.
Associated with acidosis and hypokalaemia.
What happens in type 4 renal tubular acidosis?
Type 4 RTA:
Aldosterone deficiency/resistance.
Associated with acidosis and hyperkalaemia.
What are the 4 main causes of hyperkalaemia?
Renal impairment (CKD) – Main cause
Decreased renin – Type 4 renal tubular acidosis (RTA), NSAIDs
Drugs – ACE inhibitors (ACEis), ARBs, K+ sparing diuretics (e.g., Spironolactone)
K+ release from cells – Rhabdomyolysis, acidosis
How does renal impairment (CKD) cause hyperkalaemia?
Reduced glomerular filtration rate (GFR) leads to decreased potassium excretion.
What drugs can cause hyperkalaemia? (3)
ACE inhibitors (ACEis)
Angiotensin receptor blockers (ARBs)
Potassium-sparing diuretics (e.g., Spironolactone)
How does rhabdomyolysis or acidosis cause hyperkalaemia?
Rhabdomyolysis releases intracellular K+ from damaged muscle cells.
Acidosis drives K+ out of cells in exchange for H+ ions.
What are the key ECG changes seen in hyperkalaemia? (6)
Peaked/tented T waves
Bradycardia (progressing to asystole)
Prolonged PR interval
Flattened P waves
Widened QRS
Sine waves (indicate impending cardiac arrest)
How is hyperkalaemia managed?
If K+ >6.5 mmol/L or ECG changes present:
- IV 10mL 10% Calcium Gluconate – protects the myocardium by reducing excitability.
- 10U Insulin + 50mL 50% Dextrose – drives K+ into cells.
- Alternative: Nebulised Salbutamol (beta-agonist).
-> If K+ <6.5 mmol/L: Treat the underlying cause.
-> If K+ >7 mmol/L: Recheck the sample to ensure no haemolysis.
How is hyperkalaemia managed when K+ is >6.5 mmol/L or ECG changes are present? (3 steps)
IV 10mL 10% Calcium Gluconate – Protects the myocardium by reducing excitability.
10U Insulin + 50mL 50% Dextrose – Drives potassium into cells.
Alternative: Nebulised Salbutamol (beta-agonist).
