system
Given the following post, respond as if you're commenting on Reddit:
human
Why do they medically induce comas? and what would happen to the patient if they didn't?

Often you hear about people injuring their heads in accidents (Michael Schumacher incident promting this question) they are put into a medically induced comas. My question is why do they do this? and if they didn't (for example the days before they could) what would happen to the patient?
gpt
The reason this happens is to attempt to lower intracranial pressure. The brain is trapped within the skull, and there is very little space for movement or expansion.

In head trauma, whether that's due to hitting your head or an infection (e.g. Rabies!), you get a lot of inflammation. The important aspect of inflammation in this context is that blood flow increases to the brain, and lots of fluid leaks from small blood vessels increasing pressure inside the head. This basically makes things a whole lot worse for you than the original accident did. Barring head injuries that cause blood vessels to bleed, inflammation is usually the cause of death.

By giving a class of drug called barbiturates, you reduce blood flow and metabolic rate within brain tissue. This reduces inflammation, reduces swelling and gives the brain more time to recover from the initial trauma without it being made a whole lot worse by the inflammation. The metabolic reduction is what causes the 'coma' aspect; it reduces glucose metabolism and essentially pauses higher brain function.

If you didn't give the drug, the pressure would likely increase enough to cause irreversible brain damage -- not only to higher brain function, but often to essential processes for survival.