Potassium Flashcards
What is normal serum concentration of potassium?
3.5-5.3mmol/L
Where is potassium normally distributed around the body?
Majority is intracellular (140mmol/L) and the extracellular amount is the amount we measure (3.5-5)
Where is potassium filtered in the kidney
Majority is reabsobed in the proximal tubule, 20-30% in the loop of henle and around 10% in the distal tubule
If plasma K+ is raised what 3 things will be stimulated?
RAAS system increases aldosterone that increase K+ excretion. Increased insulin and catecholamines cause extracellular potassium to be taken up into cells
At what times will the RAAS system be stimulated?
In hypotension, in Conn’s, Cushings and renal artery stenosis.
For the latter three this will cause hypokalaemia
What can cause an underactive RAAS system and what is the result of this in terms of potassium?
Spironolactone (aldosterone receptor antagonist), ACE inhibition and adrenal insufficiency can all cause RAAS dysfunction.
This means that potassium will not be excreted and will hence cause hyperkalaemia.
How can an underactive RAAS system be diagnosed?
Using short synacthen test (ACTH) which will cause no response
What happens to potassium in metabolic acidosis?
It is not able to be excreted at the kidney due to the Na/H transporter being picked over the Na/K transporter. This is the same in the blood because the K+ will move out of the cells in exchange for H+. Both of these cause hyperkalaemia.
What happens to potassium in metabolic alkalosis?
Hypokalaemia because H+ will move extracellularly in exchange for K+. K+ will be excreted in the urine.
What happens to potassium in high chloride?
To preserve neutrality, K+ is lost in the urine aswell as the chloride.
What effect will chronci hyper or hypokalaemia have?
They will cause an ajustment of what the body considers normal so in hyperkalaemia this will stimulate the kidneys to take up more K+ and prolong hyperkalaemia
What are the ECG changes seen with hyperkalaemia?
Tall tented T waves
What are the three main systems effects of hyperkalaemia?
Neuromusclar system - weakness, paralysis and parasthesia
Gastrointestinal complications - include nausea, vomiting, pain
Cardiovascular - arrhythmias, arrest
What drugs commonly cause hyperkalaemia?
Heparins, Trimethoprim (affects distal tubule), K+ sparing diuretics, Nsaids with compromised renal perfusion
What is the acute treatment of hyperkalaemia?
Calcium gluconate - increases myocyte threshold potentials and reduces chance of arrest
Insulin dextrose or glucose - to redistribute potassium back into cell
