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Internal MedicineNephrologyHyperkalemia

Hyperkalemia: MCCQE1 Preparation Guide

Hyperkalemia is a potentially life-threatening electrolyte abnormality frequently encountered in both outpatient and inpatient settings. For the MCCQE1, mastering the recognition, etiology, and acute management of hyperkalemia is essential. This topic falls under the Medical Expert CanMEDS role, requiring prompt clinical reasoning and decision-making.

🚨 Critical Concept

Hyperkalemia is a medical emergency. The most immediate danger is cardiac arrhythmia and sudden death. Stabilizing the cardiac membrane is always the first priority in a patient with ECG changes.

Definition and Epidemiology

Hyperkalemia is defined as a serum potassium concentration > 5.0 to 5.5 mmol/L.

  • Mild: 5.5 – 5.9 mmol/L
  • Moderate: 6.0 – 6.4 mmol/L
  • Severe: ≥ 6.5 mmol/L (or any level with ECG changes)

In the Canadian context, hyperkalemia is prevalent among patients with Chronic Kidney Disease (CKD), diabetes, and heart failure—conditions widely managed in Canadian primary care and internal medicine.

Etiology: The “MACHINE” Mnemonic

Understanding the cause is vital for long-term management. Use the mnemonic MACHINE to recall common causes during your MCCQE1 preparation.

LetterCauseDetails
MMedicationsACE inhibitors, ARBs, NSAIDs, Potassium-sparing diuretics (Spironolactone), Beta-blockers, Digoxin toxicity, Cyclosporine.
AAcidosisMetabolic acidosis causes H+ to enter cells and K+ to exit (transcellular shift).
CCellular DestructionRhabdomyolysis, Tumor Lysis Syndrome, Hemolysis, Burns, Trauma.
HHypoaldosteronismAddison’s disease, Type 4 Renal Tubular Acidosis (RTA).
IIntakeExcessive dietary intake (rare with normal renal function), salt substitutes.
NNephrons (Renal Failure)Acute Kidney Injury (AKI) or Chronic Kidney Disease (CKD). Most common cause.
EExcretion ImpairedObstruction, constipation (rarely sole cause).
💡

Pseudohyperkalemia: Before acting on an isolated lab value in an asymptomatic patient, consider hemolysis during venipuncture (traumatic draw) or prolonged tourniquet application. If suspected, repeat the sample.

Clinical Presentation

Most patients are asymptomatic until potassium levels are severely elevated. When symptoms occur, they are primarily neuromuscular and cardiac.

  • Neuromuscular: Generalized weakness, ascending paralysis, paresthesias, depressed deep tendon reflexes.
  • Gastrointestinal: Nausea, vomiting.
  • Cardiac: Palpitations, arrhythmias, cardiac arrest.

ECG Changes (High Yield for MCCQE1)

The progression of ECG changes is a classic MCCQE1 examination topic. Note that changes do not always follow a linear progression.

Step 1

Peaked T Waves: Tall, narrow, symmetric T waves (often the earliest sign).

Step 2

PR Prolongation & P Wave Flattening: As levels rise, conduction slows through the atria. P waves may disappear.

Step 3

QRS Widening: Conduction slows through the ventricles. This is an ominous sign.

Step 4

Sine Wave Pattern: Fusion of the QRS and T wave. Precedes ventricular fibrillation (VF) or asystole.

Diagnostic Approach

1. History and Physical

  • Medication Review: Look for RAAS blockers (Ramipril, Valsartan), NSAIDs (Ibuprofen, Naproxen), or K-sparing diuretics.
  • Diet: High potassium foods (bananas, potatoes, avocados).
  • Comorbidities: CKD, Diabetes, Heart Failure.

2. Laboratory Investigations

  • Serum Electrolytes: Confirm K+, check Na+, Cl-, HCO3- (for acidosis).
  • Creatinine & Urea: Assess renal function (AKI vs. CKD).
  • Glucose: Assess for hyperglycemia/DKA.
  • Digoxin Level: If indicated.
  • CK & Myoglobin: If rhabdomyolysis is suspected.
# Useful Calculation for Transcellular Shift
# Not typically calculated at bedside, but conceptually important:
# For every 0.1 decrease in pH, Serum K+ increases by approx 0.6 mmol/L

Management

Management is divided into three pillars: Stabilize, Shift, and Eliminate.

MCCQE1 Strategy: C-BIG-K DROP

Calcium gluconate, Beta agonists/Bicarbonate, Insulin, Glucose, Kayexalate (Resonium), Diuretics/Dialysis.

Indication: ECG changes (Peaked T waves, wide QRS) or K+ > 6.5-7.0 mmol/L.

  • Calcium Gluconate: 10 mL of 10% solution IV over 2-3 minutes.
    • Effect: Antagonizes membrane excitability.
    • Onset: Immediate (< 5 mins).
    • Duration: 30-60 mins.
    • Note: Calcium Chloride provides 3x more calcium but is irritating to veins (use central line if possible or in cardiac arrest).

Canadian Guidelines & Context

In Canada, management aligns closely with guidelines from the Canadian Society of Nephrology and emergency medicine protocols.

  1. Availability of Agents: Sodium Zirconium Cyclosilicate (Lokelma) is Health Canada approved but coverage varies by province. For MCCQE1, know the standard “Insulin/Glucose” and “Calcium Gluconate” protocols as they are universal.
  2. Dialysis Access: In remote Canadian communities, access to hemodialysis may be limited. Transfer protocols (Medevac) are relevant for “Rural and Remote” considerations in the exam.
  3. Dietary Counselling: Referencing “Canada’s Food Guide” and specific renal diets is part of the Health Advocate role.

Key Points to Remember for MCCQE1

  • ECG is King: If the stem mentions hyperkalemia, your immediate thought is “Look at the ECG.”
  • Order of Operations:
    1. Calcium Gluconate (if ECG changes present).
    2. Insulin + D50 (Shift).
    3. Kayexalate/Dialysis (Eliminate).
  • Digoxin Toxicity: Calcium was historically contraindicated in Digoxin toxicity due to “stone heart” theory, but modern literature suggests it is safe if given slowly. However, Digibind (Digoxin Immune Fab) is the specific antidote.
  • Pseudohyperkalemia: Always on the differential for an asymptomatic patient with a difficult blood draw.

Sample Question

Clinical Scenario

A 68-year-old male with a history of End-Stage Renal Disease (ESRD) on hemodialysis presents to the Emergency Department after missing his last two dialysis sessions. He complains of generalized weakness and palpitations. His vitals are BP 110/70 mmHg, HR 58 bpm, RR 18/min.

An ECG is performed immediately and reveals sinus bradycardia with wide QRS complexes and tall, peaked T-waves.

Question

Which one of the following is the most appropriate immediate management step?

  • A. Administration of 10 units IV regular insulin and D50W
  • B. Administration of 10 mL of 10% Calcium Gluconate IV
  • C. Administration of Sodium Polystyrene Sulfonate (Kayexalate) orally
  • D. Urgent Hemodialysis
  • E. Nebulized Salbutamol 10 mg

Explanation

The correct answer is:

  • B. Administration of 10 mL of 10% Calcium Gluconate IV

Detailed Analysis

  • Why B is correct: This patient has severe hyperkalemia with ECG changes (wide QRS, peaked T-waves). This is a medical emergency. The immediate priority is membrane stabilization to prevent progression to ventricular fibrillation or asystole. Calcium gluconate antagonizes the effect of potassium on the cardiac membrane without altering serum potassium levels. It works within minutes.
  • Why A is incorrect: While Insulin and Glucose will shift potassium intracellularly, this takes 15-30 minutes to have an effect. It is the second step after membrane stabilization in unstable patients.
  • Why C is incorrect: Cation exchange resins (Kayexalate) work very slowly (hours) and are used for elimination, not acute stabilization.
  • Why D is incorrect: Hemodialysis is the definitive treatment and the most effective way to remove potassium, but it requires time to organize (mobilize team, set up machine). You must stabilize the heart while arranging dialysis.
  • Why E is incorrect: Salbutamol is an adjunctive therapy for shifting potassium but is not the first-line immediate stabilizer for cardiac protection.

References

  1. Medical Council of Canada. (n.d.). MCCQE Part I Clinical Decision-Making and Multiple-Choice Questions. Retrieved from mcc.ca 
  2. Kidney Disease: Improving Global Outcomes (KDIGO). (2012). Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease.
  3. Canadian Cardiovascular Society. Guidelines on the Management of Cardiac Arrhythmias.
  4. Tintinalli, J. E., et al. (2020). Tintinalli’s Emergency Medicine: A Comprehensive Study Guide (9th ed.). McGraw-Hill Education.
  5. Toronto Notes. (2023). Nephrology Chapter: Electrolyte Disturbances. Toronto Notes for Medical Students, Inc.
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