The incident happened Friday at Brookdale Medical Center in Brownsville, Brooklyn.
Police say 40-year-old Kwincii Jones attacked his nurse while she was preparing to discharge him from the hospital.
Jones allegedly knocked 70-year-old Evelyn Lynch to the ground and stomped on her head.
She was knocked unconcious and suffered severe facial fractures.
"The whole family believe that, they are very distraught over this, and we're asking for all the prayers we can get," family friend Dr. Marvo Forde said. "We never expected that in a place she is caring for a patient that it would happen."
The beating stopped after another nurse walked in the room and saw what was happening. Jones locked himself inside of a bathroom until the police arrived and locked him up.
Lynch has already undergone brain surgery and remains in critical condition at Kings County Hospital.
Investigators are still not sure what set off the violent attack.
Brookdale Hospital released a statement addressing the nurse attack, saying:
"This was a tragic incident and we are cooperating fully with NYPD to make sure justice is administered. The Brookdale family, coworkers, staff, and administration have her and her family in our thoughts and prayers."