Without knowing the details, it doesn't sound good.
From what little I can tell, it sounds like his primary injury was to his head - what is termed a "traumatic brain injury" (TBI). These can range from a mild concussion to being essentially brain dead. The problem can be due to a focal bleed (subdural or epidural hematoma, which can be surgically evacuated but can be life threatening if not treated early enough - Natasha Richardson died from an epidural hematoma from falling on a ski slope, for example), or from diffuse swelling - what is termed cerebral edema and diffuse axonal injury (DAI). Secondary brain injury after the initial insult can aggravate things as well.
Some things I would like to know:
1. Was he intubated (had a breathing tube put in) in the field, on arrival to the hospital, or later?
2. What was his best Glascow Coma Score (GCS)? That's a standardized clinical score ranging from 3 (very bad) to 15 (normal) to assess neurologic status. A GCS of 3 on arrival with no subsequent improvement would suggest a dire prognosis.
3. What is the nature of his traumatic injury - a focal bleed, diffuse edema, brainstem injury, etc. What did his CT scan show?
4. Did he have surgical intervention.
Those things would give a better sense of what his prognosis might be. But it sounds bad.
