The two female employees suffered minor injuries as they restrained the 22-year-old man who was being treated at Newham General Hospital in Plaistow, east London. He is thought to have mental health problems.
One of the victims, a woman in her 60s, suffered serious head injuries in the attack during the early hours of Saturday but
was last night in a stable condition, the Metropolitan Police
An "improvised weapon" was used to strike the victims, police added.
The three males and one other female patient who were assaulted are in a stable condition at the hospital.
The force was alerted to the incident at 00.40am and arrested the man on suspicion of a public order offence. .
It is believed the injured patients were asleep when they were attacked.
A hospital trust spokeswoman said neither drugs nor alcohol were involved.