Moderate severe traumatic brain injury management

A 24-year-old man is brought to the emergency department with a severe head injury from a motorcycle crash and is intubated upon arrival. What should be the initial focus of management for this patient?

1: Performing a head CT scan
2: Initiating anti-seizure prophylaxis
3: Ensuring adequate oxygenation
4: Giving mannitol for potential elevated intracranial pressure