A 58-year-old man with a 10-year history of diabetes mellitus type 2 presents to the emergency department with a 3-day history of fever, cough, and dyspnea. On examination, he is drowsy, blood pressure 88/54 mmHg, heart rate 118/min, respiratory rate 28/min, and oxygen saturation 89% on room air. Skin is warm and flushed. Laboratory findings: WBC 18,500/μL, blood glucose 380 mg/dL, arterial pH 7.28, HCO₃⁻ 12 mEq/L, lactate 4.2 mmol/L, and positive blood cultures for Gram-negative organisms. Chest X-ray shows bilateral infiltrates. After securing airway and initiating high-flow oxygen, which of the following is the most appropriate immediate next step in management?