Cardiac Arrest due to electrolyte disturbance Flashcards
Causes of hyperkalaemia?
- Renal dysfunction - AKI, CKD escalation
- Rhabdomyolysis/tissue breakdown (due to alcoholism, drugs, haemolysis, tumour lysis)
- Drugs: Use of K sparing diuretics, ACEIs/ARBs etc.
(β-Blockers, acute digitalis toxicity, succinylcholine, ACE inhibitors, angiotensin receptor blockers, nonsteroidal anti-inflammatory drugs, spironolactone, amiloride) - Addison’s (aldosterone -> K+ excretion)
- Metabolic acidosis
- Blood transfusions
- Burns/other RBS destruction disease process.
- T1DM.
Which patient groups are at risk of cardiac arrest due to hyperkalaemia?
Renal failure, severe burn victims, cardiac failure, diabetes mellitus.
Monitor renal function - consider diet/med impacts
Normal range potassium?
3.5-5mmol/l
Hyperkalaemia vs severe hyperkalaemia?
> 5.5, severe = >6.5
Why do small changes in potassium concentration have big effects?
The concentration gradient between K+ in IC space and EC space provides concentration gradient for excitation of tissues
Increase in extracellular potassium - effect on myocytes?
Depolarisation.
Initially opens some sodium channels/deactivates some.
Above a certain level: depolarisation inactivates sodium channels and opens potassium channels -> refractory myocytes.
What does refractory mean?
Impossible to evoke an AP
At which stage in the cardiac cycle is the myocyte depolarising/refractory?
T wave: will not allow another AP to start.
This explains why it is so large on the hyperkalaemic ECG
Why is the P wave flattened/absent in hyperkalaemia?
P wave - atrial depolarisation. If myocytes are refractory it cannot depolarise.
What happens to acid/base balance with potassium concentration changes?
If serum K is increased -> acidosis.
If it is decreased -> alkalosis.
(K exchanged with H ions to maintain pH)
What is pseudo-hyperkalaemia?
Clotting - releases potassium from cells and platelets
Why do beta blockers cause hyperkalaemia?
Beta-2 receptor stimulation decreases EC potasisum, if this is blocked then EC potassium will rise.
Why are adrenaline/noradrenaline protective against hyerkalaemia in intense exercise?
Due to action on beta-2 receptors: increase uptake of K into cells.
Symptoms of hyperkalaemia?
Weakness -> flaccid paralyis
Paresthesia
Confusion
Lethargy
Signs of hyperkalaemia?
Weak deep tendon reflexes
ECG abnormalities
Arrthymias
Arrest