A 28-year-old woman is brought to the trauma centre 20 minutes after a fall from a 15-foot scaffold. On primary survey: GCS 14 (opens eyes to pain, confused speech, withdraws to pain), airway patent with cervical spine precautions in place, respiratory rate 20/min with oxygen saturation 94% on room air, heart rate 102/min, blood pressure 118/76 mmHg. Pupils are equal and reactive. There is no obvious external bleeding. What is the most appropriate next immediate action?