The shocking incident is one of four “serious incidents” that took place at the Archway hospital in November and is being investigated.
It came after the patient absconded from the emergency department before being admitted. They and the other patient’s relative were both left with cuts and lacerations.
Also that month a patient who had been sectioned absconded from a ward while staff were dealing with another person. They have still not been found.
Another patient died after deteriorating following an elective surgery for a giant hiatus hernia. The other serious incident was a stillbirth.
A spokesperson for Whittington Health NHS Trust said: “We are currently investigating these incidents and will ensure any necessary lessons are learned.”