Potassium and electrolytes Flashcards
Where is Potassium found?
Potassium has typically low serum concentrations i.e. [3.5-5mmol/L]
-> This is because it is an abundant intracellular cation
Which hormones are involved in renal regulation of potassium?
- Angiotensin II
2. Aldosterone
What is Renin stimulated by?
i) Reduced Perfusion
ii) Low Sodium
What is Aldosterone release stimulated by?
i) Angiotensin II at the Adrenals
ii) Rise in K+
What is the action of aldosterone?
Aldosterone increases the number of Patent Sodium Channels on the Luminal Membrane of the Distal Cortical Collecting Cells.
- > The Na+ rushes into the cells from the lumen (increased sodium reabsorption)
- > Lumen becomes negative
- > To maintain the electrochemical gradient, K+ rushes into the lumen (i.e. urine)
What are causes of hyperkalaemia?
i) RAAS inhibiting (MOST IMPORTANT)
Renal Impairment (AKI)
Drugs (ACEi, ARBs, Spironolactone) + NSAID’s
Reduction in Renin/Aldosterone (Type 4 Renal Tubular Acidosis, Addison’s)
ii) Cellular Release
-> Rhabdomyolosis
-> Acidosis
Any acidotic state causes the cells to take up H+ as a buffer and a result, release their K+ to maintain electroneutrality
iii) Foods
- > Dried Fruits
- > Banana
- > Coffee
- > Chocolate
What is the action of aldosterone?
Aldosterone increases the number of Patent Sodium Channels on the Luminal Membrane of the Distal Cortical Collecting Cells.
- > The Na+ rushes into the cells from the lumen (increased sodium reabsorption)
- > Lumen becomes negative
- > To maintain the electrochemical gradient, K+ rushes into the lumen (i.e. urine)
How would you manage a patient with hyperkalaemia of more than 6.5 or ECG changes? Give doses
- > 10ml 10% Calcium Gluconate (Stabilise Cardiac Membrane)
- > 10Units of Insulin + 50 ml 50% Dextrose. (Insulin drives K+ into cells, Dextrose prevents Hypoglycaemia)
- > Adj. Nebulised Salbutamol if required
- > Identify and treat the cause
What are the causes of hypokalaemia?
- GI loss
-> Diarhoea and Vomiting
Tend to have a low Urinary Potassium as they are holding on to it - Renal loss
- > Hyperaldosteronism, cushings – Aldosterone:Renin Ration
- > Increased Sodium Delivery to Distal Nephron, e.g. Thiazide diuretics (therefore more sodium reabsorption and more potassium loss)
- > Osmotic Diuresis - Redistribution into the cells
- > Insulin (Iatrogenic, Insulinoma, Refeeding Syndrome)
- > Beta Agonist i.e. Salbutamol use
- > Alkalosis i.e. Intracellular H+ is exchanged for extracellular K+ to act as a buffer
What are the clinical features of hypokalaemia?
- Muscle weakness
- Cardiac arrythmia
- Polyuria & polydipsia (nephrogenic DI - resistance to ADH)
How might you get increased sodium delivery to distal collecting tubule and what effect does it have on potassium?
Triple Transporter Failure- Loop Diuretics, Bartter’s Syndrome
Double Transporter Failure- Thiazide Diuretics, Gitelman’s Syndrome
As there is more sodium that is delivered to the Collecting Cells of the Distal Collecting Tubule
- > More sodium influxed through the ENaC cells
- > This causes more K+ to efflux to maintain the electrochemical gradient
What screening test would you order in a patient with hypokalaemia and hypertension?
Aldosterone: Renin ratio
Conn’s = aldosterone high and renin suppressed
How might you get increased sodium delivery to distal collecting tubule and what effect does it have on potassium?
Triple Transporter Failure- Loop Diuretics, Bartter’s Syndrome
Double Transporter Failure- Thiazide Diuretics, Gitelman’s Syndrome
As there is more sodium that is delivered to the Collecting Cells of the Distal Collecting Tubule
- > More sodium influxed through the ENaC cells
- > This causes more K+ to efflux to maintain the electrochemical gradient
What screening test would you order in a patient with hypokalaemia and hypertension?
Aldosterone: Renin ratio
Conn’s = aldosterone high and renin suppressed
How would you manage a patient with hypokalaemia?
If Serum Potassium is 3-3.5mmol/L
-> Oral Potassium Chloride (SandoK tablets TDS i.e. three times a day)
If Serum Potassium is <3mmol/L
-> IV Potassium Chloride
Maximum at 10mmol/L (>20 can be irritating to veins*)
Identify and Treat the underlying cause
