Potassium - Hypokalaemia

Hypokalaemia is defined as a serum potassium of

Hypokalaemia generally means hypomagnesaemia, measure and replace Mg2+ as required.

Causes

Symptoms

  • Usually asymptomatic, but…

  • Weakness, lethargy, paralysis, tetany

  • Cardiac dysrhythmias if severe:

    • VT, VF, heart block, asystole

Investigations

Bloods EUC ideally via Venous Blood Gas.

ECG done early on suspicion of electrolyte abnormalities:

  • Normal, flattened T waves, peaked P waves

  • U wave.

Management

Cardiac monitoring and treatment of cause are the underlying principles. The rate of replacement and methods are highly dependent on the symptoms and signs and degree of deficit.

If mild

  • Oral K replacement - 40mmol in 4-6 hours with K+ tablets, SlowK and SpanK ( swallowede whole and 8mmol per tablet) Chlorvescent (dissolved, 14 mmol/L)

  • Slow K not as effective as effervescent immediate release and less K+

  • Oral is usually best but can lead to GI upset

Replacement of magnesium - 10mmols over 20 minutes which is invariably low in hypokalaemia.

If moderate to severe K 2.5- 3.0mmol/L and asymptomatic

  • Replace as per mild if can take oral

  • Consider IV replacement as for severe

If moderate to severe K

  • IVI Potassium Chloride ideally use preloaded infusions e.g. 30mmol/L in 1000 mLs, or 10mmol/100 mLs, usually at rates of 10-20mmols per hour

  • Via central or large peripheral IV line, greater than 10 mmol/hr can cause discomfort and vein damage in peripheral lines

  • Maximum 40mmol per hour

  • Cardiac monitoring whilst infusing

  • Concurrent oral can be used if conscious

Note: 20mmol K will raise serum K by 0.5-0.75mmol l-1, this can vary and is only a guide depending on the cause ongoing losses and state of hydration.

If severe K

  • 10mmol as a push dose

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