A 28-year-old man is brought to the emergency department after a high-speed motor vehicle collision. He is immobilised on a spine board. Vitals: BP 80/50 mm Hg, HR 132 beats/min, RR 24 breaths/min, SpO2 95% on 15 L/min oxygen by mask. According to ATLS principles adapted in Canadian trauma care, what is the most appropriate next step?