A 71-year-old female with a 5-year history of diabetes mellitus (DM) presents with cough, productive sputum, and fever for 1 week, somnolence for 2 days, and coma for 5 hours. Physical exam: moderate coma, dry skin, respiratory rate 24/min, bilateral pulmonary rales, heart rate 120/min. Lab results: blood glucose 31.2 mmol/L, urine ketones (++), pH 7.1, blood urea nitrogen (BUN) 25 mmol/L, creatinine (Cr) 204 μmol/L, white blood cell count (WBC) 12×10^9/L, neutrophils 90%. Which is the best treatment option?