It's strange. Our local Ollie's, a surplus store, has ample sheets. However, these sheets have patterns and are not solid colors like the ones in hospitals. Does that make a difference? Nonetheless, if I were a hospital running low on sheets, I would use whatever is available.

Jeanette Isabelle

Hospitals need sheet that can washed at 90°C for hygiene reasons. Patterned sheets often require lower temperatures.
Patterns may also hide leaked bodily fluids. That can be bad thing.

UK hospitals used to use plain white 100% cotton sheets, more recently they have changed to cotton and polyester also in plain white.
Generally vigoursly washed in very hot water, They last on average for about 100 cycles of use and laundering before becoming lost, stolen, ripped, damaged, or stained irrecoverably.

Patterned sheets are avoided for the reasons already given, but could be used in an emergency.

Hospital sheets are usually longer than those used in the home.