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Hypokalaemia

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Rapid IV infusions of K can be harmful and must be given in a controlled and closely monitored. The rate of infusion should not normally exceed 40 mmol given in 1 L over 4-6 hours unless life-threatening arrhythmias and profound hypokalaemia and this should be managed in an HDU/CCU environment

Initial Hypokalaemia Management: Severe if K⁺ < 2.5 mmol/L
ABC, Telemetry if severe, Identify any cause - Loop Diuretics , Diarrhoea Severe (K⁺<2.5 mmol/L) then IV N-Saline + 40 mmol/L KCl over 4 hrs via infusion pump. Can also give Oral Potassium e.g. Sando K 2-3 tablets BD or TDS Cautions giving K⁺ if oliguric - take renal advice. Never give bolus IV KCl Correct any low Magnesium. Hold any Loop diuretics Those with low Mg, long QT or on Digoxin are at increased risk off arrhythmias

Initial Hypokalaemia Management: Severe if K⁺ < 2.5 mmol/L

ABC, Telemetry if severe, Identify any cause - Loop Diuretics , Diarrhoea

Severe (K⁺<2.5 mmol/L) then IV N-Saline + 40 mmol/L KCl over 4 hrs via infusion pump.

Can also give Oral Potassium e.g. Sando K 2-3 tablets BD or TDS

Cautions giving K⁺ if oliguric - take renal advice. Never give bolus IV KCl

Correct any low Magnesium. Hold any Loop diuretics

Those with low Mg, long QT or on Digoxin are at increased risk off arrhythmias

Aetiology

Potassium (K⁺) is the major intracellular cation
98% of the total pool being located in the cells at a concentration of 140-150 mmol/l
Only 2% in the extracellular fluid, where it ranges between 3.5 and 5 mmol/l.
Insulin, Beta agonists (Salbutamol/Albuterol) and alkalosis promote K⁺ entry into cells
A fine regulation of the intracellular-extracellular gradient is crucial for life, as it is the main determinant of membrane voltage; in fact, acute changes of K⁺ plasma levels may have fatal consequences.

Causes

Cause	Clinical Features	Investigations	Treatment
Diuretics (Loop and Thiazide)	Muscle weakness, cramps Fatigue ECG changes: U waves, flattened T waves Arrhythmias	Serum potassium level Serum magnesium level (often low with diuretic use) Renal function tests ECG	Oral potassium supplementation IV potassium if severe Consider stopping or reducing dose of diuretics Correct magnesium if deficient
Gastrointestinal Losses (Vomiting, Diarrhea)	Weakness, fatigue Dehydration Hypotension Arrhythmias	Serum electrolytes Bicarbonate levels (metabolic alkalosis) Renal function tests Stool studies if diarrhea is persistent	Rehydration with oral or IV fluids Oral potassium replacement Antiemetics for vomiting Antidiarrheal medications as needed
Hyperaldosteronism	Hypertension Muscle cramps, weakness Fatigue Metabolic alkalosis	Serum potassium and sodium levels Plasma aldosterone and renin levels Abdominal imaging (CT or MRI) to assess adrenal glands	Spironolactone or eplerenone (aldosterone antagonists) Surgery if adrenal adenoma is present Potassium supplementation as needed
Magnesium Deficiency	Muscle weakness, cramps Fatigue Arrhythmias Neuromuscular irritability	Serum magnesium level Serum potassium level ECG Renal function tests	Magnesium supplementation (oral or IV) Potassium supplementation Monitor serum levels of potassium and magnesium
Insulin Administration	Muscle cramps, weakness Fatigue Hypokalemia-induced arrhythmias Paralysis in severe cases	Serum potassium level Glucose levels ECG Monitor potassium levels closely during insulin therapy	Oral or IV potassium supplementation Adjust insulin dosing if possible Frequent monitoring of serum potassium

Clinical

Weakness, palpitations, Lethargy
Severe : Arrhythmias: torsades de pointes. Heart failure
Rhabdomyolysis, Severe weakness can cause diaphragmatic weakness

Investigations

FBC: usually normal.
U&E: K⁺ normal is 3.5 - 5.0 mmol/L. Moderate when 2.5-3.0 mol/L. Severe when K⁺ < 2.5 mmol/L.
Check Ca²⁺, Mg²⁺ is often all that is warranted
Investigate excessive vomiting as needed
Colonoscopy if PR mucus +++
Venous HCO₃ may be increased and suggests hypokalaemia is chronic
Tests for Conn/ Cushing as required
ECG: long PR interval, depressed ST segment, T wave changes and U waves are characteristic features of hypokalaemia. Rarely ventricular tachycardia and other arrhythmias.

Management

ABC, IV fluids, as needed. Investigate and treat any cause. Telemetry if severe.
Mild to Moderate K consider Oral replacement with oral KCl as Sando-K 2 tabs TDS is sufficient until normal K⁺ for most patients and then review.
Sando-K contains 12mmol of potassium and 8mmol of chloride, which are preferable. Avoid prescribing long term unless justified. These can be prescribed either 2-3 tablets BD or TDS.
Severe Hypokalaemia with significant arrhythmias: when K⁺ < 2.5 mmol/L. If very severe with significant arrhythmias such as VT then IV Potassium 40 mmol/L over 1-2 hour by volumetric pump with close nursing supervision preferably in CCU/HDU as a rapid infusion can be fatal. Should be given through a central vein.
Severe Hypokalaemia and stable then slower infusions of 20-40 mmol/L over 4 hours safer. Where possible use prepared bags of 20mmol KCI in 500ml sodium chloride 0.9% or glucose 5% or 40mmol KCI in 500ml sodium chloride 0.9% or glucose 5%.
Sympathetic states: Thyrotropic periodic paralysis, theophylline overdose or head injury consider Propranolol to correct low K.
Consider also replacing phosphate f also low at the same time.

References

Management of Hypokalaemia (plasma K⁺ <3.5mmol/L) GCC

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