A 65-year-old man with end-stage renal disease (ESRD) on chronic hemodialysis presents to the emergency department with muscle weakness and palpitations. His last dialysis session was 4 days ago due to a missed appointment. ECG reveals peaked T waves, widened QRS complexes, and a sine wave pattern. Serum potassium is 7.8 mEq/L (normal: 3.5-5.0 mEq/L). Which of the following is the most appropriate next step in management?
