A 25-year-old man is brought to the emergency depament by ambulance after falling 20 ft from a ladder. He was placed on a backboard for spinal stabilization. Intravenous access was obtained en route, and he received infusion of crystalloids. The patient is unconscious upon arrival. His blood pressure is 91/44 mm Hg, pulse is 129/min, and respirations are 8/min. Pulse oximetry is at 85%. Evaluation shows several superficial facial lacerations, a depressed temporal skull fracture, and a forearm fracture. There are no periorbital or periauricular hematomas, and there is no significant neck edema. Which of the following is the most appropriate next step in management of this patient?