Thousands of NHS operations and appointments have had to be cancelled because of the nurses' strikes in England this week.
Over the two days, NHS England said 27,800 bookings had to be rescheduled, including 5,000 operations and treatments.
There were more than 30 hospital trusts affected with some saying between 10% to 20% of normal activity was lost.
They warned the dispute was hampering progress in reducing the backlog.
Saffron Cordery, of NHS Providers, which represents hospital bosses, said the strike days caused "significant disruption" and were "some of the hardest"