A 30-year-old man is brought to the emergency department after a high-speed motor vehicle collision. He is unconscious with a GCS of 6 (E1 V1 M4). Vital signs: blood pressure 90/60 mmHg, heart rate 120 bpm, respiratory rate 10 breaths/min, SpO2 88% on room air. There is no obvious external haemorrhage. According to trauma resuscitation principles, what is the most appropriate immediate intervention?