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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

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