Final answer:
The priority need for the patient is Intravenous (IV) fluids to correct dehydration and restore fluid balance.
Step-by-step explanation:
The priority need for the patient with type 1 diabetes arriving in the emergency department with a glucose level of 390 mg/dL and positive result for ketones, vital signs of 110/70 mm Hg, 120 beats/minute, and 28 deep, sighing respirations/minute is Intravenous (IV) fluids.
Ketoacidosis can be severe and, if not detected and treated properly, can lead to diabetic coma, which can be fatal. IV fluids are needed to correct dehydration and restore fluid balance in the body.
Oxygen may be required if the patient is experiencing difficulty breathing, but in this case, the priority is addressing the fluid imbalance.