Potassium and Electrolytes Flashcards
What is the serum concentration for normal potassium?
3.5-5.3 mmol/L
Most abundant INTRAcellular cation
What is potassium regulated by?
Angiotensin II + Aldosterone
What does aldosterone contribute in terms of electrolyte balance?
Aldosterone is stimulated by Angiotensin II and K+
Aldoesterone causes resorption of Na+ and water and excretion of K+ in urine
Describe the renin angiotensin aldosterone system
Renin from JGA stimulates release of angiotensinogen from liver
Converted to angiotensin I
ACE in Lung converts to angiotensin II
Stimulates adrenals to release Aldosterone
Aldosterone acts on principal cells of cortical collecting tubule
What does high potassium stimulate the adrenals to produce?
Aldosterone
To increase potassium loss in urine + maintain potassium in homeostatic range
What are the main causes of hyperkalaemia?
Renal impairment: reduced renal excretion
Drugs: ACEi, ARBS, spironolactone
Low aldosterone: Addison’s disease, Type 4 renal tubular acidosis (low renin, low aldosterone)
Release from cells: rhabdomyolysis, acidosis
What are ECG changes with hyperkalaemia?
Tented T waves
Broad QRS
What is the treatment for hyperkalaemia?
If ECG changes + K+ >6.5:
10ml 10 % calcium gluconate to stabilise cardiac myocardium
100ml 20% dextrose + 10 units insulin bolus
Nebulized salbutamol
Treat underlying cause
What are causes of hypokalaemia?
GI loss: vomiting
Renal Loss: MR excess, osmotic diuresis
Redistribution into cells: insulin, beta-agonists, alkalosis
What are the clinical features of hypokalaemia?
Nephrogenic DI: resistant to ADH- polyuria + polydipsia.
Muscle weakness
Arrhythmia
How do you manage hypokalaemia?
Serum K+ 3.0-3.5 mmol/L:
Oral potassium chloride (2 SandoK tablets tds for 48h)
Recheck serum K+
Serum K+ < 3.0 mmol/L:
IV potassium chloride
Max rate 10 mmol per hour
(Rates > 20 mmol per hour are highly irritating to peripheral veins)
Treat the underlying cause e.g. spironolactone
Which drug can cause hyperkalaemia?
Furosemide
Bendroflumethiazide
Salbutamol
Ramipril
Ramipril
Which drug can cause hypokalaemia?
Spironolactone
Indomethacin
Perindopril
Furosemide
Furosemide
Describe the action of aldosterone on the principal cells
Binds to mineralocorticoid receptors
Leads to less degradation of Na channels, increasing no. of open channels
Increases Na reabsorption
Lumen becomes more -ve
K+ moves into lumen down electrochemical gradient
What are the stimuli for aldosterone secretion?
Angiotensin II
High K+
How does renal impairment lead to hyperkalaemia?
Low GFR e.g. in kidney disease/ drugs = reduced K+ excretion
Low renin e.g NSAIDs, T4 renal tubular acidosis in DM. Less angiotensinogen released + converted, less AII, less aldosterone = reduced K+ excretion
How do ACE inhibitors cause hyperkalaemia?
Give 3 examples
Less AI converted to AII
Less aldosterone
Less K+ lost
Enalapril, Ramipril, Lisinopril
How do angiotensin receptor blockers cause hyperkalaemia?
Give 2 examples
Block AII receptors
Less AII action
Less aldosterone
Less K+ lost
Losartan, Candesartan
How does Addison’s disease lead to hyperkalaemia?
Less Aldosterone
Less K+ lost
How do aldosterone antagonists cause hyperkalaemia?
Give an example
Less Aldosterone action
Less K+ lost
Spironolactone
How does rhabdomyolysis cause hyperkalaemia?
K+ leaks from damaged muscle cells in long lie
How does acidosis cause hyperkalaemia?
H+ moves into cells
K+ lost to maintain electrochemical neutrality
What is the alternative dose of dextrose you could give in hyperkalaemia?
200ml of 10% dextrose
What can cause renal loss of K+ and lead to hypokalaemia?
Hyperaldosteronism e.g. Conns + excess cortisol e.g. Cushings
Increased Na delivery to distal nephron
Osmotic diuresis e.g. hyperglycaemia lose K+
