I am a nurse and have a quick question

Dr. G mentioned "respirator brain" and stated that if someone has been on a vent/resp for a "while" that the brain can actually become liquid....

how does this work when some people are on resp/vents for a long period of time and then wake up and have a full recovery....

Is the brain like a muscle that starts to get firm with use again???

Thanks for helping me with my odd question of the day that is driving me nuts LOL