Biochemistry- K+ Flashcards
Why is maintaining potassium concentration so vital?
Pottasium helps set up the resting membrane potential of cells, so changing its concentration can lead to excitability of cells e.g. nerve and heart cells.
What are the two most important factors that affect potassium excretion?
Glomerular filtration rate
Plasma potassium concentration.
Where is potassium lost from?
A small amount lost from the gut (5mmol/day)
Rest from the kidneys.
What factor, other than increased excretion, can affect potassium balance?
Redistribution of potassium. Most of the bodies potassium (98%) is inside the cell. If there is significant tissue damage, this potassium can go elsewhere, disturbing the balance.
When is hyperkalaemia thought to be severe?
When the potassium levels >7mmol- this is immediately life threatening.
What ECG changes may you see in hyperkalaemia?
Tall ‘tented’ T waves
Widening of the QRS complex
(This reflects altered myocardial contractility).
What other symptoms may you get with hyperkalaemia?
Muscle weakness
Parathesia (reflecting impact of K+ on muscles and nerves).
How can hyperkalaemia be categorised?
Increased intake
Redistribution
Decreased excretion
Why may you get reduced excretion causing hyperkalaemia?
Renal failure-reduced GFR means the kidneys can’t excrete pottasium.
Hypoaldosteronism-Aldosterone stimulates sodium reabsorption in the distal tubules in return for excreting potassium and hydrogen. This is most often due to use of ACE inhibitors and ARBs
What causes redistribution of potassium?
Potassium release from damaged cells- occurs in rhabdomyalsis, tumour lysis syndrome.
Metabolic acidosis- There is a relationship between conc of H+ ions and potassium. As H+ increases, it displaces potassium from inside the cell.
Insulin deficiency- Insulin stimulates cellular uptake of potassium. If there is insulin deficiency or resistance, hyperkalaemia can ensue.
Hyperkalaemic periodic paralysis- rare family disorder. Presents as frequent attacks of muscle weakness or paralysis.
What are the causes of increased intake of pottasium?
Many drugs are given as potassium salts.
Sometimes blood products give excess potassium.
How quickly can IV potassium be given?
Should not be given at greater than 20mmol/ hour except in extreme cases.
How do you treat hyperkalaemia?
Calcium gluconate- counteracts the effects of hyperkalaemia on resting membrane potentials
Insulin and glucose- to promote uptake of potassium by tissues.
Look for underlying cause of reduction in GFR.
