Close to 400 such hospitals operate around the country, some free-standing, others located within other hospitals, most for-profit. They provide daily physician visits, high nurse-to-patient ratios and intensive therapy.

In 2017, they accounted for about 174,000 hospital stays. Yet the odds look dismal for older adults who enter an L.T.C.H., Dr. Makam and his colleagues reported in a recent study in the Journal of the American Geriatrics Society.

The researchers defined “recovery” as logging 60 consecutive days without entering a hospital or nursing home — “a pretty low bar,” Dr. Makam said. But over five years, more than half of Medicare patients in an L.T.C.H. never reached it.

Moreover, “true recovery rates — getting back to thinking clearly and functioning well — may be lower,” Dr. Makam said.

In fact, despite the prevalence of aggressive, life-prolonging procedures like feeding tubes, ventilators and dialysis, L.T.C.H. patients spent two-thirds of their remaining lives (the median survival period was 8.3 months) in institutions, including hospitals, skilled nursing homes and rehab facilities.

“A little over a third of people never make it home,” Dr. Makam said. “They go back and forth between the L.T.C.H. and hospitals and nursing facilities, and they die in one of them.”

Patients described their quality of life as poor, complaining of hunger, thirst, difficulty communicating. “People were bored,” Dr. Lamas said. “They couldn’t move. There was a deeper sense of being alone, feeling trapped.” Their families felt anxious and stressed.