"Ponte della cavana dell'Ospedale Civile" on the Fondamente Nuove, Castello,
built in 1886 over a very small canal used to moor boats transporting the sick.
The canal is so small and separated from the building that it is hard to imagine that
it's still in use.
On the other side of the hospital, on the Fondamenta dei Mendicanti,
there is another bridge seemingly without a rio. However that bridge was built over
a covered canal that leads inside the hospital. I imagine that's the canal in use today
to transport the patients into the building.