Regulation of Potassium Flashcards
(30 cards)
What is the normal potassium range?
3.5 - 5.5 mmol/L
Relationship between extracellular {K+] and resting membrane potential
- If extracellular [K+] rises, RMP decreases > depolarised
- if extracellular [K+] falls, RMP increases > hyperpolarised
Hypokalemia signs on ECG
prolonged PR interval
ST depression
Shallow T wave
Prominent U wave
Hyperkalemia signs on ECG
Small P wave
Prolonged PR interval
Widened QRS
Tall, peaked T wave (first sign)
.
casues sinusoidal pattern + asystole
Where is most potassium reabsorbed in the nephron?
PCT
What happens to potassium in the collecting duct?
Secreted
What cells in the collecting duct control acid base balance + K+ regulation?
Intercalated cells
a - acidosis
B - alkalosis
Causes of hyperkalaemia
Lack of excretion:
- spironolactone, ACEi/ARBs
- metabolic acidosis
- AKI
- Addison’s disease
Release from cells:
- cell death e.g. crush injury, rhabdomyolysis
Excess administration:
- K+ supplements
- high dietary intake
- massive blood transfusion
What drugs can cause hyperkalaemia?
- potassium sparing diuretics e.g. spironolactone
- ACEi
- ARBs
- ciclosporin
- heparin
what foods are high in potassium?
- salt substitutes (contain K+ instead of Na+)
- bananas
- oranges
- kiwi
- tomatoes
Short term treatment of hyperkalaemia
- IV calcium gluconate 10ml of 10%: Ca2+ stabilises myocardium > prevents arrhythmias (no affect on K+)
- IV combined insulin/dextrose: drives K+ into cells to lower plasma conc. | given with glucose to avoid hypoglycaemia
Further management of hyperkalaemia
- nebulised salbutamol
- oral/enema calcium resonium: increases K+ excretion from bowels
- loop diuretics
- stop exacerbating drugs + treat underlying cause
What is the only way to increase K+ excretion without renal replacement therapy?
Calcium resonium
Excreted in bowels
Long term treatment of hyperkalaemia
- Low potassium diet
- Stop offending meds
- furosemide > enhances K+ loss in urine | give IV fluids to prevent dehydration
- haemodialysis
When is haemodialysis considered as management of hyperkalemia?
patients with AKI + persistent hyperkalaemia
Causes of hypokalaemia with alkalosis
- vomiting
- thiazide + loop diuretics
- cushing’s syndrome
- primary hyperaldosteronism (conn’s syndrome)
Causes of hypokalaemia with acidosis
- diarrhoea
- renal tubular acidosis
- partially treated DKA
Clinical effects of hypokalaemia
- Muscle weakness, cramps, tetany (spasms)
- vasoconstriction + cardiac arrhythmias
- impaired ADH action > thirst, polyuria, not concentrated urine
- metabolic alkalosis due to increased intracellular [H+]
Treatment of hypokalaemia
Treat the cause
IV potassium replacement At a rate of 10mmol per hour
What can you use for potassium replacement?
- oral: bananas, oranges, avocados
- IV: add KCl to IV bags
- potassium sparing diuretics e.g. spironolactone, amiloride
Which intercalated cells treat acidosis?
How do they do this?
Alpha intercalated cell
- H2O + CO2 > H+ + HCO3-
- H+ into lumen via H+ ATPase and HK ATPase
- HCO3- reabsorbed into into blood in exchange for Cl-
Which intercalated cells treat alkalosis?
How do they do this?
Beta intercalated cells
- H2O + CO2 > H+ + HCO3-
- HCO3- exchanged with Cl- into the lumen
- H+ into blood via H+ ATPase and HK ATPase
What is the effect of regulation of acidosis on K+ levels?
- K+ is reabsorbed into blood as a result of H+ K+ ATPase
- in all cells in the body H+ is taken up in exchnage for K+
- can result in Hyperkalaemia
What is the effect of regulation of alkalosis on K+ levels?
- K+ is lost from the cell + blood as it enters the nephron lumen
- in all cells in the body K+ is taken up in exchange for H+
- can result in hypokalaemia
