CHEMPATH: Potassium Handling Flashcards
What is the normal potassium serum concentration?
3.5-5 mmol/L
What is the most abundant intracellular cation?
Potassium
Which hormones are involved in renal regulation of potassium?
- Angiotensin II
- Aldosterone
What is the exchange in the renal tubules with potassium?
Na+ into blood leading to water retention
K+ into renal tubules
Why does it make sense for high K+ to increase aldosterone production?
It means that K excretion can occur in the cortical collecting tubules
Describe the movement of potassium down an electrical gradient in this diagram.
- Potassium moves through the potassium channels (ROMK) down an electrical gradient into the lumen.
- Aldosterone binds to mineralocorticoid receptors and causes an increase in the sodium channels.
- When you have more sodium channels you absorb more sodium from the lumen. This means that the lumen becomes more negative (i.e. less positive).
- Therefore potassium can move down the electrical gradient and be excreted.
Describe the molecular pathway which causes aldosterone to express more Na channels and more K to be excreted.
- Adosterone binds to mineralocorticoid receptor
- This leads to expression of the Sgk-1 ( a kinas) which leads to inhibition of Nedd4
- Nedd4 leads to degradation of sodium channels (ENaC - epithelial sodium channels) so if you degrade less you have more Na channels
How do you get polyuria in Conn’s syndrome?
Hypokalaemia causes resistance to ADH
What are the stimuli for aldosterone secretion?
- Angiotensin II
- Aldosterone
Which K abnormality will you get with:
- Reduced GFR
- Reduced renin
- Ang II receptor blockade
- Addison’s disease
- Aldosterone antagonists
- Reduced GFR - you will have hyperkalaemia
- Reduced renin - e.g. type 4 renal tubular acidosis (diabetic nephropathy) and NSAIDs, causes hyperkalaemia
- ACE2 - less AngII means less aldosterone which causes hyperkalaemia
- AngII receptor blockade e.g. losartan causes hyperkalaemia
- Addison’s - damage to adrenals so less aldosterone production so more potassium retained
- Aldosterone antagonists e.g. spironolactone
i.e. all hyperkalaemia.
What causes K to ‘leak out’ of cells?
What are the main causes of hyperkalaemia?
- Renal impairment - reduced renal excretion
- Drugs - ACEi, ARBs, spironolactone
- Low aldosterone e.g. Alddison’s
- Release from cells - rhabdomyolysis, acidic state
What ECG change is associated with hyperkalaemia?
How do you manage a patient with hyperkalaemia?
In practice we use 100mL of 20% dextrose with insulin (which drives potassium into cells). You give the dextrose to make sure the patient doesn’t become hypoglycaemic.
What K level/clinical findings would suggest you need to treat the hyperkalaemia?
K+ over 6.5 mmol/L
OR
ECG changes
Which ions is potassium reabsorbed with in the renal tubules?
Summarise the management of hypokalaemia.
What is the volume status? What is the cause? What is the sodium level?
- Hypovolaemia
- Caused by D+V
- Hyponatraemic - when volume is replaced
What is the volume status? What is the cause? What is the management?
Hypervolaemic
Fluid restrict and treat underlying cause
What type of liver disease? What is the volume status?
Excess NO in cirrhosis –> low BP –> hyponatraemia due to water retention
Hypervolaemic
Treat underlying cause and fluid restrict.
What is the clinical assessment?
hypothyroidism
hydrocortisone and fludrocortisone
Short synacthen test
Addison’s
SIADH caused by lung cancer
Pituitary adenomas rarely cause DI - this is central DI.
What investigations should you do if you suspect DI?
Check for DM as this is more common first.
Which drug is causing hyperkalaemia?
Ramipril
What investigation would you do in this patient?
Aldosterone/renin ratio
