K and electrolytes

Question 1

what is the most abundant intracellular cation

Answer 1

K

Question 2

normal serum K

Answer 2

3.5-5 mmol/L

Question 3

what hormones are involved in reg of K in kidney

Answer 3

• Aldosterone
  
  • Angiotensin II

Question 4

summarise the renin-angiotensin-aldosterone system

Answer 4

• Angiotensin produced in liver - converted to ang 1 and then ang II by ACE in lung
• Ang II stim adrenal cortex -> aldosterone
• -> Na in and K out through urine
• Happens in principle cells in cortical collecting tubules

If a lot of aldosterone = low K

K also stim aldosterone release = lose K in urine

Question 5

summarise how Na movement alters K movenment

Answer 5

• More Na comes in = lumen more -ve = loss of K down the electrical gradient
• Na and K don’t move in same transporter
• It is the fact that the na makes the lumen -ve which pushes the K out down the electrical gradient

Question 6

how does aldosterone alter K movement

Answer 6

Aldosterone = increase number of open Na channels = reabsorb more Na = more -ve lumen = electrical gradient = more K secreted into lumen

Question 7

what are the stimuli for aldosterone secretion

Answer 7

K
Angiotensin II

Question 8

causes of hyperkalaemia

Answer 8

• Reduced GFR ie renal failure
• Low renin - ie diabetic nephropathy, NSAIDs - less Angiotensin to ANg1 = less aldosterone = less K secretion. renin produced in juxtaglomerula apparatus
• ACEi - less Ang1->ANg2 = less K loss
• ARB - losartan. Block ang2 receptor = less ang2 action = less loss K
• Addisons -> low aldosterone
• Aldosterone antagonist - spirionolactone = less aldosterone action = less K secretion

Release from cells
- rhabdomyolysis
- Acidosis - H ions move into cells - K lost to maintain electroneutrality = high k

Question 9

ECG with hyperkalaemia

Answer 9

peaked T waves

Question 10

mx of hyperkalaemia - need to know dose

Answer 10

• 10ml 10% ca gluconate - stabalise myocardium
• 100ml 20% dextrose and 10 units insulin
• Nebulised salbutamol
• Treat underlying cause

Question 11

causes of hypokalaemia

Answer 11

GI loss - vomiting

Renal loss
* excess cortisol (bind mineralocorticoid receptor) or excess aldosterone (Conn’s or bilateral hyperplasia)
* Increase na distally
* Osmotic diuresis

Redistribution into cells
* B cell agonist stim K uptake into cells
* Insilin
* Alkalosis - H move out of cell, and K move into the cell.

Rare cayuses - renal tubular acidosis type 1 and 2, hypomagnesia

Question 12

summarise renal loss of K

Answer 12

If block resporption with loop diuretics eg furosemide - more Na will go to DCT - so more K will be lost. Eg with loop diuretics or bartter syndrome

Thiazide diuertics and gitelman syndrome - same thing more distally - more Na reabsorbed more distally -> more -ve lumen -> more k lost

ie deliver more na to distal tubles

Question 13

sx of hypokalaemia

Answer 13

• Muscle weakness
  
  • Cardiac arrhythmia
  • Polyuria and polydupsia - hypok gives you nephrogenic DI

Question 14

Screening test if low K and htn

Answer 14

aldosterone:renin ratio

Question 15

mx of hypokalaemia

Answer 15

Serum potassium 3.0-3.5 mmol/L
* Oral potassium chloride (two SandoK tablets tds for 48 hrs)
* Recheck serum potassium

Serum potassium < 3.0 mmol/L
* IV potassium chloride
* Maximum rate 10 mmol per hour
* Rates > 20 mmol per hour are highly irritating to peripheral veins

Treat the underlying cause e.g. spironolactone