Final answer:
Cervical spine immobilization using a collar should be administered as soon as a spinal injury is suspected during the secondary assessment of an unresponsive trauma patient to prevent further injury.
Step-by-step explanation:
During the secondary assessment of an unresponsive trauma patient, cervical spine immobilization collar should be applied as soon as a spinal injury is suspected, before moving the patient, and ideally before any significant movement has occurred. While advanced imaging techniques such as magnetic resonance imaging (MRI) or computed tomography (CT) scanning can accurately localize spinal injuries, in emergency settings and particularly on-scene, immediate manual stabilization followed by the application of a cervical spine immobilization collar is recommended to mitigate the risk of exacerbating any potential spinal injury.