Hyperkalaemia: A Guide for Junior Doctors

Introduction:

Hyperkalaemia, defined as a serum potassium level above 5.5 mmol/L, can be life-threatening if not promptly recognized and managed. Potassium plays a critical role in maintaining cellular function, particularly in muscle cells, including the heart. Elevated levels can result in dangerous arrhythmias. This guide aims to help junior doctors navigate the history-taking, examination, investigations, and management of hyperkalaemia in an easy-to-understand manner.

History-Taking: What to Ask

When assessing a patient with suspected hyperkalaemia, ask targeted questions to uncover the underlying cause and assess severity. Key areas to focus on include:

·       Symptoms of Hyperkalaemia:

• Muscle weakness or paralysis: Ask if the patient has noticed generalized muscle weakness, fatigue, or difficulty moving.

• Palpitations or chest pain: These can indicate cardiac involvement.

• Shortness of breath: Dyspnoea may be related to cardiac arrhythmias or acidosis.

• Paraesthesia: Sensory disturbances, especially around the lips or extremities, may be due to hyperkalaemia.

·       Medications:

• ACE inhibitors/ARBs, potassium-sparing diuretics (e.g., spironolactone): Ask if the patient is taking these, as they reduce potassium excretion.

• NSAIDs: These can also impair potassium excretion.

• Supplemental potassium or herbal remedies: Overuse or misuse can lead to hyperkalaemia.

• Recent use of IV fluids or blood transfusions: Large volumes of stored blood contain elevated potassium levels.

·       Underlying Medical Conditions:

• Renal failure: Ask about known chronic kidney disease or recent changes in urine output, as decreased renal clearance is a major cause.

• Endocrine issues: History of Addison’s disease or adrenal insufficiency could indicate impaired aldosterone function, leading to potassium retention.

• Trauma, burns, or recent surgery: Cellular breakdown releases potassium.

• Acidosis: This can shift potassium out of cells.

·       Dietary Intake:

• High potassium diet: Excessive intake of potassium-rich foods (bananas, tomatoes, oranges) or salt substitutes should be queried.

  
  

Examination Findings: What to Look For

A systematic examination is crucial to assess the impact of hyperkalaemia on various organ systems, particularly the heart, muscles, and kidneys.

·       General Inspection:

• Altered mental status: Confusion or lethargy may indicate severe hyperkalaemia.

• Signs of dehydration or volume overload: Look for dry mucous membranes or peripheral oedema, which might hint at renal dysfunction.

·       Cardiovascular System:

• Pulse: Bradycardia or irregular heart rate may indicate arrhythmias.

• Blood pressure: Hypotension could suggest severe cardiovascular compromise.

• Heart auscultation: Listen for irregular beats or signs of heart failure, such as murmurs or added heart sounds (e.g., S3).

·       Neuromuscular System:

• Muscle weakness: Check for diminished motor strength, especially proximally.

• Hyporeflexia: Reflexes may be diminished in severe cases.

• Respiratory muscles: Monitor for signs of respiratory muscle weakness, as this can be life-threatening.

·       Renal System:

• Fluid status: Assess for oliguria or anuria, which may suggest acute kidney injury.

• Abdominal examination: A palpable bladder might suggest urinary retention.

Investigations: What to Order

·       Electrolytes (U&E):

• A serum potassium level >5.5 mmol/L confirms hyperkalaemia. Severity is classified as:

• Mild: 5.5–5.9 mmol/L

• Moderate: 6.0–6.4 mmol/L

• Severe: ≥6.5 mmol/L

·       ECG:

• Early changes: Peaked T waves.

• Progressive changes: Flattened P waves, prolonged PR interval, and widened QRS complexes.

• Life-threatening changes: Sine wave pattern, ventricular fibrillation, or asystole.

·       Arterial Blood Gas (ABG):

• Look for metabolic acidosis (low pH, high anion gap), which may indicate impaired potassium clearance or an underlying cause like DKA.

·       Renal Function Tests:

• Check for elevated creatinine and blood urea nitrogen (BUN) to assess renal impairment.

·       Blood Glucose:

• Hyperkalaemia can occur in diabetic emergencies like diabetic ketoacidosis (DKA).

·       Other Blood Tests:

• Full Blood Count (FBC): Look for signs of haemolysis or infection.

• Cortisol levels: If Addison’s disease is suspected.

Management Plan: What to Do

The management of hyperkalaemia revolves around stabilizing the myocardium, shifting potassium into cells, and removing excess potassium from the body.

·       Stabilize the Heart:

·       Calcium gluconate (30 mL of 10% solution IV over 5–10 minutes): This stabilizes cardiac myocytes and prevents arrhythmias but does not lower potassium.

·       Shift Potassium into Cells:

·       Insulin and glucose (10 units of insulin with 50 mL of 50% dextrose IV): This drives potassium into cells.

·       Nebulized salbutamol (10–20 mg): Beta-2 agonists help shift potassium into cells.

·       Sodium bicarbonate (50 mmol IV): Use in cases of metabolic acidosis to facilitate potassium uptake by cells.

·       Remove Potassium from the Body:

·       Loop diuretics (e.g., furosemide): Promote renal excretion of potassium.

·       Sodium polystyrene sulfonate (Kayexalate): Binds potassium in the gut, though this is slow-acting.

·       Haemodialysis: This is the most definitive treatment for severe or refractory hyperkalaemia, especially in patients with renal failure.

·       Monitor and Reassess:

·       Continuous ECG monitoring is essential until potassium levels are normalized.

·       Repeat serum potassium and ECGs every 1–2 hours to guide ongoing treatment.

·       Treat the Underlying Cause:

·       Renal failure: Optimize renal function or consider dialysis.

·       Medication review: Discontinue potassium-sparing drugs or supplements.

·       Endocrine disorders: Address adrenal insufficiency with corticosteroids if necessary.