A 23-year-old woman with type 1 diabetes is brought to the emergency department with abdominal pain, vomiting and drowsiness. She stopped her insulin 2 days ago due to illness. Vitals: HR 120 bpm, BP 98/60 mmHg, RR 28 breaths/min, Kussmaul respirations. Capillary glucose is 24 mmol/L and ketones are 5.5 mmol/L. What is the most appropriate initial management step?