Hyperkalemia

Introduction

Hyperkalemia is a critical electrolyte disorder that Canadian medical students must thoroughly understand for the MCCQE1 exam. This comprehensive guide covers essential aspects of hyperkalemia, tailored to the Canadian healthcare context and MCCQE1 preparation.

Definition and Diagnosis

Hyperkalemia is defined as a serum potassium level greater than 5.5 mmol/L. In the Canadian healthcare system, it's crucial to recognize that:

• Mild hyperkalemia: 5.5-6.0 mmol/L
• Moderate hyperkalemia: 6.1-7.0 mmol/L
• Severe hyperkalemia: >7.0 mmol/L

Etiology

Understanding the causes of hyperkalemia is crucial for MCCQE1 success. Here are the main categories:

1. Increased Potassium Intake

   • Excessive dietary intake
   • Blood transfusions
   • Potassium supplements

2. Decreased Renal Excretion

   • Acute or chronic kidney disease
   • Medications (e.g., ACE inhibitors, ARBs, potassium-sparing diuretics)
   • Hypoaldosteronism

3. Transcellular Shift

   • Acidosis
   • Insulin deficiency
   • Beta-blockers
   • Cell lysis (e.g., tumor lysis syndrome, rhabdomyolysis)

4. Pseudohyperkalemia

   • Hemolysis during blood draw
   • Extreme leukocytosis or thrombocytosis

Clinical Presentation

For the MCCQE1, it's essential to recognize that hyperkalemia can present with:

• Muscle weakness
• Paralysis
• Paresthesias
• Cardiac arrhythmias (potentially fatal)

However, many patients may be asymptomatic, especially in mild cases.

ECG Changes

ECG changes progress with increasing severity of hyperkalemia:

1. Peaked T waves
2. PR interval prolongation
3. P wave flattening/disappearance
4. QRS widening
5. Sine wave pattern (pre-cardiac arrest)

Diagnostic Approach

For MCCQE1 preparation, understand the Canadian approach to diagnosing hyperkalemia:

Treatment

Treatment of hyperkalemia in the Canadian healthcare setting follows these principles:

1. Cardiac Membrane Stabilization

   • Calcium gluconate 10% solution: 10 mL IV over 2-3 minutes
   • Repeat ECG after administration

2. Intracellular Shift of Potassium

   • Insulin: 10 units regular insulin IV with 25g dextrose
   • Beta-2 agonists: Salbutamol 10-20 mg nebulized or 0.5 mg IV

3. Potassium Removal

   • Diuretics: Furosemide 40-80 mg IV
   • Sodium polystyrene sulfonate: 15-30 g orally or rectally
   • Hemodialysis for severe cases or renal failure

4. Treat Underlying Cause

   • Adjust medications
   • Manage renal failure
   • Correct acidosis if present

Canadian Guidelines

The Canadian Society of Nephrology provides guidelines for managing hyperkalemia in chronic kidney disease:

1. Dietary potassium restriction (<2-3 g/day) for CKD patients with hyperkalemia
2. Consider fludrocortisone for hypoaldosteronism in CKD if not contraindicated
3. Use of potassium binders (e.g., patiromer, sodium zirconium cyclosilicate) in select cases

Key Points to Remember for MCCQE1

• 🍁 Hyperkalemia definition: >5.5 mmol/L in Canadian labs
• 🏥 ECG changes are crucial for diagnosis and severity assessment
• 💊 Common causes in Canada: CKD, medications (ACE inhibitors, ARBs), diabetes
• 🚑 Treatment priority: Cardiac stabilization, then potassium lowering
• 🩺 Canadian approach emphasizes confirming diagnosis before extensive treatment
• 📊 Familiarity with Canadian guidelines for CKD-associated hyperkalemia

Sample Question

# Sample Question

A 68-year-old woman presents to the emergency department with generalized weakness and nausea. She has a history of hypertension and type 2 diabetes mellitus. Her medications include metformin, ramipril, and hydrochlorothiazide. On examination, she appears lethargic. Vital signs are: BP 150/90 mmHg, HR 52 bpm, RR 18/min, Temperature 36.8°C. ECG shows peaked T waves and a widened QRS complex. Serum potassium is 7.2 mmol/L, creatinine 180 μmol/L. Which of the following is the most appropriate initial management?

- [ ] A. Administer sodium polystyrene sulfonate
- [ ] B. Start hemodialysis
- [ ] C. Give furosemide 80 mg IV
- [ ] D. Administer calcium gluconate 10% solution
- [ ] E. Give insulin 10 units with 25g dextrose IV

Explanation

The correct answer is:

• D. Administer calcium gluconate 10% solution

Explanation: This patient has severe hyperkalemia (7.2 mmol/L) with ECG changes, indicating a medical emergency. The most appropriate initial management is to stabilize the cardiac membrane with calcium gluconate 10% solution. This helps prevent potentially fatal arrhythmias. After this, treatments to lower potassium levels (such as insulin with dextrose, or hemodialysis) should be initiated. While all the other options are valid treatments for hyperkalemia, cardiac stabilization takes priority in severe cases with ECG changes.

References

1. Levin, A., et al. (2008). Guidelines for the management of chronic kidney disease. CMAJ, 179(11), 1154-1162.

2. Clase, C. M., et al. (2020). Potassium homeostasis and management of dyskalemia in kidney diseases: conclusions from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference. Kidney International, 97(1), 42-61.

3. Kamel, K. S., & Halperin, M. L. (2015). Fluid, Electrolyte and Acid-Base Physiology E-Book: A Problem-Based Approach. Elsevier Health Sciences.

4. Canadian Diabetes Association Clinical Practice Guidelines Expert Committee. (2018). Diabetes Canada 2018 Clinical Practice Guidelines for the Prevention and Management of Diabetes in Canada. Can J Diabetes, 42(Suppl 1), S1-S325.

5. Daly, K., & Farrington, E. (2013). Hypokalemia and hyperkalemia in infants and children: pathophysiology and treatment. Journal of Pediatric Health Care, 27(6), 486-496.