A 72-year-old male with chronic kidney disease presents to the emergency department with profound weakness and an ECG showing peaked T-waves and a widened QRS complex. His serum potassium level is 7.2 mEq/L. Which immediate intervention is most critical to stabilize his cardiac membrane?

✓ Correct Answer: Option B

Intravenous calcium gluconate is the most critical immediate intervention to stabilize the cardiac membrane in severe hyperkalemia, especially when ECG changes are present. Insulin with dextrose shifts potassium into cells, and furosemide or sodium polystyrene sulfonate remove potassium, but calcium directly protects the heart.