A 45-year-old male patient has undergone a traumatic injury and is being prepared for transport. What is the BEST method to assess his pain level to ensure proper management during transport?
Relying on the patient's medical history to estimate his pain level.
Asking the patient to rate his pain on a numerical scale from 0 to 10.
Using the patient's vital signs to infer the severity of pain.
Observing the patient's body language and facial expressions to determine pain level.