A 72-year-old man with a history of chronic kidney disease stage 4, hypertension, and type 2 diabetes presents to the emergency department with confusion and lethargy. His family reports that he has been increasingly drowsy over the past two days. On examination, he is disoriented to time and place, with a blood pressure of 150/90 mmHg, heart rate of 88 bpm, respiratory rate of 20 breaths per minute, and temperature of 36.5°C. Laboratory tests reveal: sodium 130 mmol/L, potassium 5.8 mmol/L, bicarbonate 18 mmol/L, urea 25 mmol/L, creatinine 450 µmol/L, and glucose 8 mmol/L. An ECG shows peaked T waves. What is the most appropriate immediate management step?