A mental health patient was unlawfully shackled to an emergency department bed at the Royal Adelaide Hospital for four days, the State Ombudsman has found.

The man, who had been charged with a minor offence, complained to the Office of the Public Advocate after he was shackled to a bed at the hospital in September.

In a report into the incident, Ombudsman Richard Bingham found Correctional Services staff acted unlawfully by restraining the man who was deemed low-risk and appeared to be calm and co-operative.

Public Advocate John Brayley says his client found the incident distressing and humiliating.

"This person was in this situation because of a minor incident related to the person's mental illness," he said.

"They were low-risk, the person didn't need to be shacked. The person needed to be in a mental health bed.

"He was shackled with metal shackles, three-point restraints over a four-day period, thee nights. He had to use a bottle to urinate."

The Ombudsman's findings come after Health Minister Jack Snelling ordered a review of mental health bed closures following complaints that a shortage is causing long waits in emergency departments.

Dr Brayley says his client would not have needed restraining if a bed in a ward was available.

"In most of those cases where people have been in an emergency department for longer than four hours, that shackling would not be needed if the person could be looked after in a ward because mechanical restraint shackles are almost unheard of in wards," he said.

The Correctional Services Department has promised to change its procedures and says the Ombudsman's recommendations are being implemented.