A 58-year-old man with type 2 diabetes mellitus and chronic kidney disease (eGFR 28 mL/min/1.73m²) presents to the emergency department with palpitations and muscle weakness. He reports taking lisinopril and spironolactone for 2 years. On examination, blood pressure is 142/88 mmHg, heart rate 92/min. ECG shows peaked T waves in precordial leads and prolonged PR interval. Serum potassium is 7.2 mEq/L, creatinine 2.8 mg/dL, and pH 7.32. What is the most appropriate immediate intervention?

Explanation

## Clinical Context This patient has **severe symptomatic hyperkalemia** (K⁺ = 7.2 mEq/L) with **ECG changes** (peaked T waves, prolonged PR interval) indicating cardiac membrane instability. The combination of CKD, ACE inhibitor, and aldosterone antagonist created a perfect storm for potassium retention. ## Immediate Management Hierarchy **Key Point:** Cardiac membrane stabilization is the FIRST priority in symptomatic hyperkalemia with ECG changes, regardless of the serum K⁺ level. ### Why Calcium Gluconate Is Correct 1. **Mechanism**: Calcium raises the threshold potential of the cardiac myocyte membrane, reducing the gradient between resting potential and threshold. This stabilizes the myocardium against arrhythmias. 2. **Onset**: Works within **1–3 minutes** — critical in symptomatic disease. 3. **Does NOT lower K⁺**: It is a **temporizing measure** only, buying time for definitive therapies. 4. **Dose**: 10% solution, 10–20 mL IV over 2–3 minutes; may repeat in 5 minutes if ECG changes persist. **High-Yield:** Calcium is given FIRST in symptomatic hyperkalemia with ECG changes. It is the only agent that directly protects the heart. ## Subsequent Therapies (After Stabilization) Once the myocardium is stabilized, shift K⁺ **intracellularly** and then **remove** it: | Agent | Mechanism | Onset | Duration | K⁺ Shift (mEq/L) | |-------|-----------|-------|----------|------------------| | **Insulin + Dextrose** | Drives K⁺ into cells via Na⁺-K⁺-ATPase | 10–20 min | 4–6 hrs | 0.5–1.2 | | **Beta-2 agonist** (salbutamol) | Activates β₂ receptors → ↑ Na⁺-K⁺-ATPase | 30 min | 4–6 hrs | 0.5–1.0 | | **Sodium bicarbonate** | Alkalosis shifts K⁺ in (weak effect in acidosis) | 30–60 min | 2–4 hrs | 0.3–0.5 | | **Diuretics** (furosemide) | ↑ Urinary K⁺ excretion | 1–2 hrs | Variable | Depends on urine output | | **Cation exchange resin** (sodium polystyrene sulfonate) | Binds K⁺ in GI tract | 2–4 hrs | 4–24 hrs | 0.5–1.0 per dose | | **Hemodialysis** | Removes K⁺ directly | Immediate | Ongoing | 1–2 per hour | **Clinical Pearl:** In this patient with eGFR 28, **diuretics alone are inadequate** because urine output is already compromised. Hemodialysis will likely be needed after stabilization. ## Mnemonic for Hyperkalemia Management **SHIFT then REMOVE:** - **S**tabilize: Calcium (cardiac protection) - **H**yperpolarize: Insulin + dextrose, β₂ agonist, bicarbonate (shift K⁺ in) - **I**ncrease excretion: Diuretics, resin, dialysis (remove K⁺) - **F**inal step: Dialysis if renal failure or refractory - **T**emporizing: All medical measures buy time for definitive renal replacement ## Why This Case Requires Dialysis Eventually **Key Point:** eGFR 28 with ongoing ACE inhibitor + spironolactone use means the patient cannot excrete K⁺ adequately. Medical therapy alone will not prevent recurrence. [cite:Harrison 21e Ch 280]