Chemical Pathology 13 - Potassium & electrolytes Flashcards Preview

Year 5 Pathology ICSM - DM me for full access > Chemical Pathology 13 - Potassium & electrolytes > Flashcards

Flashcards in Chemical Pathology 13 - Potassium & electrolytes Deck (36)
Loading flashcards...
1

What is the serum concentration of potassium?

3.5 - 5

2

What are the hormones involved in renal potassium regulation?

Angiotensin II
Aldosterone

3

Where is renin released from?

Juxtaglomerular apparatus

4

Where is angiotensinogen released from?

Liver

5

Where is angiotensin I converted to angiotensin II?

Lung

6

What is the action of angiotensin II

Secretion of aldosterone from adrenals

7

What are the two stimuli for aldosterone release?

Angiotensin II
Hyperkalaemia

8

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

9

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

Then:

7. Rhabdomyolysis (damaged cells leak out potassium)

8. Acidosis (H+ enters cell, K+ moves into lumen following electrochemical gradient)

10

Which 3 drug classes are associated with hyperkalaemia?

ACE inhibitors
ARBs
Spironolactone

11

How can diabetic nephropathy cause hyperkalaemia?

Type 4 renal tubular acidosis - causes reduced renin which in turn reduces aldosterone --> less K+ excretion

12

What ECG change is associated with hyperkalaemia?

Peaked T waves

13

Why is hyperkalaemia not seen until late renal failure?

Initially reduced GFR --> increased aldosterone to compensate --> hyperkalaemia only occurs when compensatory mechanism falls

14

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

15

What are the 3 broad causes of hypokalaemia?

GI loss
Renal loss
Redistribution into the cells

16

Why is calcium gluconate used in hyperkalaemia?

It stabilises the membrane of cells in the myocardium (doesn't actually reduce potassium)

17

Why is insulin given in hyperkalaemia?

Drives potassium into cells

18

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

19

How does heart failure cause hyponatraemia?

Reduced CO --> reduced BP --> detected by baroreceptors --> Excess ADH --> sodium loss
ALSO
Lower BP --> lower GFR --> ADH --> sodium wasting

20

What is reabsorbed in the ascending limb of the loop of henle?

Na
K
Cl

21

What is reabsorbed in the DCT of the loop of henle?

Na
Cl

22

Give 2 causes of impaired sodium resorption in the ascending limb of the loop of henle

Loop diuretics
Barter syndrome

23

Give 2 causes of impaired sodium resorption in the DCT of the loop of henle

Thiazide diuretic
Gitelman syndrome

24

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

25

How does excess aldosterone affect potassium?

Causes increased sodium in cells --> exchanged with potassium --> hypokalaemia

26

What are the 3 mechanisms of renal loss of potassium?

Hyperaldosteronism

Increased sodium delivery to distal nephron

Osmotic diuresis

27

How does alkalosis affect potassium?

Hypokalaemia

28

What are the top 3 methods of potassium loss?

GI loss (vomiting)
Renal loss
Redistribution into cells (insulin/ beta agonists/ alkalosis - treatments for hyperkalaemia!)

29

What are the clinical features of hypokalaemia?

Muscle weakness
Cardiac weakness (arrhythmia)
Polyuria and polydipsia (somehow potassium affects ADH, causing *nephrogenic DI*)

30

What screening test would you order in a patient with hypokaleamia and hypertension?

Aldosterone: renin ratio

Decks in Year 5 Pathology ICSM - DM me for full access Class (85):