You are transporting a 35-year-old male who was found unconscious outside in below-freezing temperatures. On assessment, you find he is shivering vigorously, has a core temperature of 32°C (89.6°F), and has cold, firm skin over his extremities without immediate blanching. What is the most appropriate initial intervention to manage his condition?
Apply ice packs to his extremities to reduce tissue damage
Use passive rewarming with blankets and clothing
Administer vasopressors to stabilize his blood pressure
Initiate active external rewarming and administer warm IV fluids