Hypokalaemia

Related Subjects: Hyperkalaemia |ECG - Hyperkalaemia |Hypokalemia |Hyperkalaemic and Hypokalaemic Periodic Paralysis |Resuscitation - Advanced Life Support |Action Potential

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 (<2.5 mmol/L) then IV N-Saline + 40 mmol/L over 4 hrs via infusion pump to control rate. 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

• Starvation, Severe vomiting or diarrhoea, fluid loss to drains or sweat
• Insulin, Beta agonists (Salbutamol) and metabolic alkalosis
• Diuretics e.g. loop diuretics, thiazides
• Thyrotoxic periodic paralysis, Theophylline
• Primary hyperaldosteronism (Conn's syndrome)
• Alkalosis, Cushing's syndrome, Severe Vomiting
• Diarrhoea - mucus rich in K from a villous adenoma
• Purgatives/laxative abuse, Intestinal fistula
• Hypothermia, Pseudohypokalaemia
• Bartter syndrome, Gitelman syndrome
• Hypomagnesaemia, Insulin therapy
• Giving Vitamin B12 or folate, GMCSF or TPN in anabolic state
• Familial hypokalaemic periodic paralysis

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 Ca, 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