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hypokalaemia

hypokalaemia

see also:

  • 1g KCl = ~13mmol K+
  • all intravenous potassium chloride should be prescribed in millimols
  • potassium chloride should not be administered at a rate greater than 10mmol/hour in adults on general wards
  • the maximum peripheral concentration of potassium chloride solution is 10mmol/100ml
  • an IV monitoring pump must be used when administering potassium chloride infusion
  • do not commence potassium supplementation if there is a risk of renal failure preventing normal excretion and risking potentially fatal hyperkalaemia - check there is good urine output first!
  • to minimise risk of inadvertent potentially fatal iv bolus doses of KCl (mistakenly thought to be NSaline or water), most hospitals have removed KCl ampoules and use pre-mixed KCl 10mmol in 100ml NSaline bags to avoid confusion.

aetiology of hypokalaemia

  • redistribution of K+ into cells:
    • beta 2 adrenergic receptor activation (eg. salbutamol)
    • aldosterone - lowers slope of linear relationship of [K+]serum vs total body K
    • periodic hypokalaemic1) paralysis
    • metabolic alkalosis - for each increase in pH by 0.1 ⇒ serum [K+] decreases by ~0.6 (artificially low)
    • insulin - rarely a cause in practice
  • decreased total body potassium levels:
    • 24hr urine potassium excretion (when good urine output) can help determine whether it is renal loss or otherwise:
      • < 20mmol/day excreted in adults suggests inadequate potassium intake or GIT losses such as diarrhoea or vomiting
      • >20mmol/day excreted in adults suggests renal losses:

effects of hypokalaemia:

management of hypokalaemia

  • consider if it could be redistribution of K+ into cells which is caused by overactive Na-K ATPase pump, thus manage this rather than giving more K+ as this risks rebound hyperkalaemia.
    • examples of redistributive causes of hypokalaemia include:
      • salbutamol nebuliser therapy (or other beta 2 adrenergic agonists)
      • metabolic alkalosis - see potassium physiology for calculation to adjust [K+] for pH
      • if Asian male with weakness, consider thyrotoxic hypokalaemic periodic paralysis (TPP) 
        • Rx is beta blockers rather than K+ supplementation.
  • Rx any coexisting hypocalcaemia while treating the hypokalaemia
  • if decreased total body K rather than just redistributive:
    • ⇒ IV KCl < 0.5mEq/kg/hr to max. 20mEq/hr (usually 10mmol/hr in adults unless circumstances dictate higher rates and monitoring is used)
      • unless very high on-going K loss rates demands higher replacement rates & max. infusion concentration 40-60mEq/L;

target serum potassium level

  • normal range for K+ is 3.5 to 5.5 mmol/L.
  • in certain circumstances, the minimum level is raised to 4.0mmol/L, for the following reasons:
    • hypokalaemia promotes electro-physiological instability. Significant complications include neuromuscular and cardiac dysrhythmia dysfunction (especially in patients on digoxin).

critically ill patients or cardiac patients at high risk from adverse effects of hypokalaemia

  • cardiac monitor if severely hypokalaemic, high risk patients or those requiring infusion rates of KCl > 10mmol/hr
  • maintain K+ > 4.0 mmol/l
  • 6 hourly Serum K+ levels minimum. (2 hourly in diabetic ketoacidosis (DKA), etc.)
    • KCl ampoules are NOT to be used except in ICU
    • the only pre-mixed high concentration KCl infusion solution in WH is 100ml 0.29% saline with 10mmol KCl (= 0.75% = 0.75g)
    • other pre-mixed solutions each with 30mmol KCl (= 0.224% = 2.24g) in 1L include:
      • 0.9% saline
      • 0.18% saline with 4% glucose
      • 5% glucose
      • Hartmann's solution (modified)

usual potassium replacement guidelines for such ADULT patients

IV replacement for K+ levels of 3.6 - 3.9 is indicated only in patients who:
  • are nauseated
  • cannot tolerate oral replacement
  • are having a large diuresis due to diuretic therapy

These recommendations do not apply for certain conditions such as diabetic ketoacidosis (DKA) as these usually have different guidelines

serum K+ in mmol/L oral replacement IV replacement (see note above)
3.5 or less nil 30mmol over 3hrs
3.6 4 Slow K tablets or 20mmol over 2hrs
3.7 3 Slow K tablets or 20mmol over 2hrs
3.8 2 Slow K tablets or 10mmol over 2hrs
3.9 1 Slow K tablet or 10mmol over 2hrs
  • other keywords: hypokalemia
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hypokalemic, hypokalemia
hypokalaemia.txt · Last modified: 2019/08/17 16:27 (external edit)