A 58-year-old man with type 2 diabetes and chronic kidney disease (eGFR 22 mL/min/1.73m²) presents to the emergency department with palpitations and generalized weakness. He was started on an ACE inhibitor 2 weeks ago for hypertension. On examination, heart rate is 52/min and regular. ECG shows peaked T waves in precordial leads and prolonged PR interval. Serum potassium is 7.2 mEq/L. Which of the following is the MOST appropriate first-line intervention?

Explanation

## Clinical Presentation & Pathophysiology **Key Point:** This patient has symptomatic hyperkalemia with ECG changes (peaked T waves, prolonged PR interval, bradycardia) indicating cardiac membrane instability and imminent risk of arrhythmia or cardiac arrest. **High-Yield:** Hyperkalemia management is stratified by presence of ECG changes: - **ECG changes present** → Stabilize cardiac membrane FIRST (calcium) - **No ECG changes** → Shift K⁺ intracellularly (insulin, β₂-agonists) or remove K⁺ (diuretics, resin, dialysis) ## Why Calcium Gluconate Is Correct Intravenous calcium gluconate (or calcium chloride) is the MOST appropriate first-line intervention in symptomatic hyperkalemia with ECG changes because: 1. **Mechanism:** Calcium antagonizes the effect of hyperkalemia on the cardiac action potential by raising the threshold potential, stabilizing the myocardial membrane and preventing arrhythmias. 2. **Onset:** Rapid onset (1–3 minutes) — critical in this patient with bradycardia and peaked T waves. 3. **Does NOT lower serum K⁺** — it buys time while definitive K⁺-lowering measures (insulin, dialysis) are arranged. 4. **Dose:** 10 mL of 10% calcium gluconate IV over 2–5 minutes (can repeat once if ECG changes persist). **Clinical Pearl:** Calcium is a **temporizing measure only** — it does not remove K⁺ from the body. After stabilization, proceed with insulin + dextrose (shifts K⁺ into cells) and/or dialysis (removes K⁺). ## Why This Patient Needs Urgent Intervention | Feature | Significance | |---------|-------------| | eGFR 22 mL/min | Severe renal impairment → impaired K⁺ excretion | | ACE inhibitor use | Reduces aldosterone → ↓ renal K⁺ excretion | | Diabetes | Risk factor for hyperkalemia (RTA, impaired cellular uptake) | | Peaked T waves + bradycardia | Cardiac toxicity — imminent risk of VF or asystole | ## Management Algorithm ```mermaid flowchart TD A[Hyperkalemia confirmed]:::outcome --> B{ECG changes?}:::decision B -->|Yes| C[IV Calcium gluconate]:::action C --> D[Stabilizes cardiac membrane]:::outcome D --> E{Renal function?}:::decision E -->|eGFR < 30| F[Hemodialysis]:::action E -->|eGFR > 30| G[Insulin + Dextrose]:::action G --> H[Shift K+ intracellularly]:::outcome F --> I[Remove K+ from body]:::outcome B -->|No| J[Insulin + Dextrose or Diuretics]:::action ``` **High-Yield:** Always remember: **Calcium first if ECG changes, then shift/remove K⁺.** [cite:Harrison 21e Ch 280]