Hyperkalaemia Flashcards
What factors reduce serum potassium?
Important hormonal factors that reduce serum potassium include insulin (causes an intracellular shift of potassium), adrenaline (beta-receptor stimulation causes intracellular shift), and aldosterone (promotes potassium excretion).
Definition of hyperkalaemia
A serum level >5.5 mmol/L is considered to be hyperkalaemia
A serum level > 6.5mmol/L = MEDICAL EMERGENCY!
Drugs that can cause hyperkalaemia
- Potassium-sparing diuretics e.g. spironolactone - COMMON
- ACE inhibitors (interfere with RAAS) e.g. ramipril - COMMON
- NSAIDs - COMMON
- Ciclosporin
- Heparin
- Beta-antagonists: inhibit cellular entry of potassium
- Digoxin: inhibitor of Na+/K+ ATPase causing reduced cellular entry of potassium
How can DKA cause hyperkalaemia
insulin resistance - insulin controls Na+/K+ pump - pumping sodium out of cell in exchange for K+. With insulin resistance, the K+ leaves the cell.
Other aetiology of hyperkalaemia
- Death of muscle fibres and release of their contents, including K+, into bloodstream caused by a traumatic CRUSH INJURY e.g. from a car accident or building collapse
- Tumour lysis syndrome
- Severe burns
- Increased load:
- Potassium chloride
- Transfusion of stored blood
What does K+ in the blood determine
amount K+ in the blood determines the excitability of nerve and muscle cells, including skeletal muscle, smooth muscle and cardiac muscle
Pathophysiology of hyperkalaemia?
When K+ levels in the blood rise - this reduces the difference in electrical potential between cardiac myocytes and outside of the cells meaning the threshold for action potential is significantly decreased resulting in increased abnormal action potential and thus abnormal heart rhythms that can result in ventricular fibrillation and cardiac arrest
smooth muscle it can cause cramping - due to depolarisation and contraction
skeletal muscle it can cause weakness and flaccid paralysis - resting potential is too high, which means muscle can’t repolarise and then contract again
Signs of hyperkalaemia
- Tachycardia (arrhythmia)
- Fast irregular pulse
- ECG differences - tall tented T waves, small P waves, wide QRS
Symptoms of hyperkalaemia
- Muscle weakness
- Muscle cramps
- Lightheadedness
- Paresthesia (tingling in skin)
- Palpitations
- Chest pain
Investigations for hyperkalaemia
- 12-lead ECG:hyperkalaemic changes include flat P waves, short QT interval, broad QRS, ST depression, and tented T waves
- U&Es:confirm high serum potassium levels
- Lithium heparin sample:rule out pseudohyperkalaemia.
- VBG:check for acidosis which may be causing the hyperkalaemia
Differential diagnosis for hyperkalaemia
- Artefactual
- DKA
- Hyperosmolar hyperglycaemic state
- Chronic kidney disease
Non urgent management of hyperkalaemia
- Treat underlying cause
- Review medication
- Can give polystyrene sulfonate resin (calcium resonium) which binds K+ in the gut and thus reduces absorption
Urgent management of hyperkalaemia
If there are signs of myocardial hyperexcitability and serum levels > 6.5mmmol/L
Cardiac membrane protection:if ECG changes are present, 10ml of 10% IV calcium gluconate or calcium chloride should be givenimmediately. If ECG changes arenotpresent this should not be given, regardless of the serum concentration - doesnt lower potassium concentration
Potassium reduction:
- Insulin/dextrose infusion: causes anintracellular shiftof potassium; the dose is 10 units actrapid with 50 ml of 50% glucose over 15 mins
- Nebulised salbutamol: causes anintracellular shiftof potassium
Other treatments for hyperkalaemia
- Haemodialysis: removes potassium from the body
- Enema - if vomiting prevents calcium resonium administration
Complications of hyperkalaemia
Broadens QRS comples
Ventricular tachycardia
Ventricular fibrillation
Cardiac arrest
