Flashcards in Chemical Pathology 13 - Potassium & electrolytes Deck (36)
What is the serum concentration of potassium?
3.5 - 5
What are the hormones involved in renal potassium regulation?
Where is renin released from?
Where is angiotensinogen released from?
Where is angiotensin I converted to angiotensin II?
What is the action of angiotensin II
Secretion of aldosterone from adrenals
What are the two stimuli for aldosterone release?
How does aldosterone work?
Acts on cortical collecting tubule (distal tubule) of nephron
Causes sodium retention and potassium excretion:
Aldosterone --> synthesis of sodium channels --> lumen becomes negative --> potassium moves down electrochemical gradient into lumen
What are the main causes of hyperkalaemia?
First go thorough RAAS:
1. Renal failure (as reduced GFR --> less renin --> less aldosterone)
2. Reduced renin (rare)
3. ACE inhibitor (less ACE --> less angiotensin II --> less aldosterone)
4. AgII receptor blocker (--> less aldosterone)
5. Addison's disease (less aldosterone)
6. MR receptor blockers = aldosterone antagonists
7. Rhabdomyolysis (damaged cells leak out potassium)
8. Acidosis (H+ enters cell, K+ moves into lumen following electrochemical gradient)
Which 3 drug classes are associated with hyperkalaemia?
How can diabetic nephropathy cause hyperkalaemia?
Type 4 renal tubular acidosis - causes reduced renin which in turn reduces aldosterone --> less K+ excretion
What ECG change is associated with hyperkalaemia?
Peaked T waves
Why is hyperkalaemia not seen until late renal failure?
Initially reduced GFR --> increased aldosterone to compensate --> hyperkalaemia only occurs when compensatory mechanism falls
How do you manage a patient with hyperkalaemia?
10mls 10% calcium gluconate (ONLY when potassium is over 6.5 or there are ECG changes)
20% dextrose + 10 units insulin (give dextrose alongside insulin to prevent hypoglycaemia)
Nebulised salbutamol (if hyperkalaemia is severe, it puts potassium into cells)
Treat the underlying cause
What are the 3 broad causes of hypokalaemia?
Redistribution into the cells
Why is calcium gluconate used in hyperkalaemia?
It stabilises the membrane of cells in the myocardium (doesn't actually reduce potassium)
Why is insulin given in hyperkalaemia?
Drives potassium into cells
When would you give fluids in a hyperkalaemic patient, as well as calcium gluconate + insulin?
If their hyperkalaemia is secondary to renal failure that is caused by hypovolaemia
How does heart failure cause hyponatraemia?
Reduced CO --> reduced BP --> detected by baroreceptors --> Excess ADH --> sodium loss
Lower BP --> lower GFR --> ADH --> sodium wasting
What is reabsorbed in the ascending limb of the loop of henle?
What is reabsorbed in the DCT of the loop of henle?
Give 2 causes of impaired sodium resorption in the ascending limb of the loop of henle
Give 2 causes of impaired sodium resorption in the DCT of the loop of henle
What is the effect on potassium of impaired sodium resorption in the nephron?
More sodium delivered to distal nephron --> sodium goes from urine into cell, making urine more negative --> potassium drawn out into urine
How does excess aldosterone affect potassium?
Causes increased sodium in cells --> exchanged with potassium --> hypokalaemia
What are the 3 mechanisms of renal loss of potassium?
Increased sodium delivery to distal nephron
How does alkalosis affect potassium?
What are the top 3 methods of potassium loss?
GI loss (vomiting)
Redistribution into cells (insulin/ beta agonists/ alkalosis - treatments for hyperkalaemia!)
What are the clinical features of hypokalaemia?
Cardiac weakness (arrhythmia)
Polyuria and polydipsia (somehow potassium affects ADH, causing *nephrogenic DI*)