Hyperkalemia refers to elevated potassium levels in the blood. Potassium is one of the most important electrolytes present in the human body and is critical to the proper functioning of nerve and muscles including heart muscle.

Potassium is present in highest concentration within the cells (in contrast to sodium found extracellularly). Any condition causing decreased potassium excretion or escape from the cells into the blood can cause hyperkalemia with serious consequences if left untreated.

Types of Hyperkalemia
Hyperkalaemia is defined as plasma potassium levels in excess of 5.5 mmol/L. The European Resuscitation Guidelines further classify hyperkalaemia according to severity as

• Mild – 5.5-5.9 mmol/L.
• Moderate – 6.0-6.4 mmol/L.
• Severe – >6.5 mmol/L.

Risk factors for development of hyperkalemia
• Extremes of age
• Uncontrolled diabetes
• Kidney disease
• Men > women
• Ingestion of drugs that influence potassium levels

Causes of Hyperkalemia

What is spurious hyperkalemia
Often a report of high blood potassium may not be true hyperkalemia. It may be caused by the
rupture of red blood cells (hemolysis) in the blood sample during or shortly after withdrawal of blood. The ruptured cells leak their potassium into the sample. This falsely raises (spurious) the amount of potassium in the blood sample, although the potassium level in the body may be actually normal. When a spurious result is suspected, the test should be repeated.

Clinical Features of Hyperkalemia
Symptoms may be vague and non-specific and include
• Generalised weakness and tiredness
• Muscle paralysis
• Shortness of breath
• Chest pain and palpitations
• Occasional bradycardia due to heart block or increased respiratory rate from respiratory muscle weakness.
• Depressed or absent tendon reflexes.

Physical examination is unlikely to point towards the diagnosis unless there is severe bradycardia associated with severely tender and painful muscles or history of drug ingestion is present

Diagnosis of Hyperkalemia – Investigations
Establishing whether it is true or spurious hyperkalemia – any doubt necessitates an urgent repeat (doing an arterial blood gas can provide an almost instant result)

Blood tests and urine tests
• Measurement of serum electrolytes including potassium (normal 3.5 to 5.5 mmol/L); any unexpected test result must be
repeated as shaking the blood sample vigorously or a delay in performing the test can give rise to spurious increase in potassium
levels
• Renal function tests including blood urea, serum creatinine (to rule out renal failure)
• Plasma glucose measurements (markedly elevated in diabetic ketoacidosis)
• Arterial blood gas measurements (to rule out metabolic acidosis)
• 24 hour urine volume and electrolytes

ECG
Serum potassium will reflect the extracellular concentration but the best way to assess the intracellular situation is an ECG and, in severe cases, continuous monitoring is required. ECG in hyperkalemia may show any of the following changes

• Tall T waves – can be difficult to determine.
• Prolonged of the PR interval.
• Widening of the QRS.
• Decreased, or loss of, P wave.
• AV dissociation.
• Asystole.

In patients with underlying heart disease and pre-existing abnormal baseline ECG, bradycardia (low heart rate) may be the only new ECG abnormal finding.
Conduction disturbances of the heart are more likely to occur there is a rapid rise in potassium – eg, acute kidney injury (AKI) and/or if associated with hypoxia due to any cause.

Treatment of Hyperkalemia
The treatment will depend upon the level of potassium, the rate of increase in serum potassium and associated ECG abnormalities

• Determine severity of hyperkalaemia – mild, moderate, severe (based on serum levels)
• 12-lead ECG and look for changes as above (ECG may be normal in severe hyperkalemia but presence of ECG changes
warrants urgent treatment)
• Determine the primary cause and treat as appropriate
• Stopping any drug/drugs that may be causing hyperkalemia
• Calcium gluconate infusion (10%) 10 ml if ECG is abnormal; administering calcium gluconate in the absence of ECG
changes is controversial and is best avoided
• Insulin-glucose infusion (usually 10 units of soluble insulin are added to 25 g of glucose) given by IV infusion to shift
potassium into cells. Blood glucose levels have to be checked before and after
• Frequent monitoring of serum potassium levels for treatment response and appropriate intervention
• Calcium polystyrene sulfonate resin (Calcium Resonium®) with regular lactulose will eliminate potassium via the digestive
tract. This method is recommended in mild to moderate hyperkalemia and administered over several days. It has no role in acute
hyperkalemia due to the long time it takes for onset of effect
• More effective newer potassium binding agents such as sodium zirconium cyclosilicate and patiromer are being developed

Management of resistant hyperkalemia
• Administration of further glucose and IV insulin and/or IV calcium.
• Use of IV diuretics (eg, furosemide) is controversial. However, this could be beneficial in the presence of associated
comorbidities such as congestive cardiac failure.
• Discussion with renal physicians if above measures fail
• Sodium bicarbonate may be useful in the setting of resistant hyperkalemia in the presence of acidosis. However, it can be
dangerous and best avoided in DKA and considered only after due consultation with renal physicians
• Hemodialysis may be helpful but it is an invasive procedure

Prevention of hyperkalemia
Many cases of hyperkalaemia is iatrogenic (drug induced eg certain antihypertensives). If a patients is taking at least two medicines known to reduce potassium excretion (NSAIDs are a common additional factor), urea and electrolytes should be immediately checked if they develop diarrhoea or vomiting.

Points to remember:
• Many instances of hyperkalemia are drug induced and a detailed drug history is important
• Patients often remain asymptomatic or have non-specific symptoms until cardiac toxicity and ECG changes develop
• Polystyrene sulfonate is given in mild hyperkalemia
• IV insulin, glucose, and calcium, and probably an inhaled beta 2-agonist is given for moderate to severe hyperkalemia
• Hemodialysis may be necessary in patients with renal impairment and marked ECG changes