A 26-year-old male is found at the bottom of a cliff face after falling approximately 10 metres while rock climbing. He is lying in a remote location accessible only by foot. The helicopter is 30 minutes away. He has a GCS of 5, is tachycardic, and has unequal pupils (right 7 mm, left 3 mm). What is the key pre-hospital neuroprotective intervention while awaiting evacuation?