Get in, get a new knee, go home. As treatments get less invasive and recovery times shrink, a new kind of hospital is cropping up — the "bedless hospital." They have all the capabilities of traditional hospitals: operating rooms, infusion suites, and even emergency rooms and helipads. What they don't have is overnight space.

"It reduces cost, and it reduces the risk of infection," said Dr. Akram Boutros, CEO of MetroHealth System, which just opened a $48 million bedless hospital near Cleveland that he expects will serve about 3,000 people in the first year. "People go home to a less-risky environment, where they tend to get better faster."

The growth in outpatient healthcare is a fundamental shift in U.S. medicine. MetroHealth, which gets part of its funding from taxpayers and serves a large Medicaid population, has expanded outpatient visits from 850,000 to 1.2 million in the last four years, a 40 percent increase.

Outpatient visits, experts say, subsidize more expensive inpatient treatment.But some observers worry that the development of bedless hospitals is part of a financial shell game hospitals must play to make the dollars match up with the care they offer. And they wonder if such facilities are diverting resources away from a large population of patients who still require more complex treatment.

"The untold story is what's happening to all of those patients who do still need to be in the hospital," said Harold Miller, chief executive of the Center for Health Care Quality and Payment Reform. "And are the places where they are going getting paid enough to support good care?" What's driving the development of bedless hospitals, said several hospital executives, are changes in reimbursement, both from the federal government and private insurers.

"Hospitals tend to be the highest-cost setting because of the intensity of services there," she said. "You see a dramatic difference in the payment for inpatient and outpatient services." The rise of bedless hospitals has also tracked the development of streamlined treatments. Several years ago, doctors at Memorial Sloan Kettering Cancer Center started brainstorming plans for more surgical space — an exercise that led to efforts to create standardize protocols for routine surgeries, such as mastectomies, that could be done without prolonged hospital stays. The end result was the Josie Robertson Surgery Center, a 16-story building on Manhattan's Upper East Side where doctors perform outpatient cancer surgeries. It has 28 short-stay beds, but most patients leave within hours of their procedures.

But under the Affordable Care Act and other reforms, reimbursement is linked more directly with the effectiveness of treatment, meaning providers are rewarded financially if they can deliver better care at a lower cost. For MetroHealth, building and buying bedless hospitals is part of a strategy to compete with Cleveland Clinic and University Hospitals. While a helipad at its new building offers the capability to treat patients facing medical emergencies, most people will come for the convenience of having all medical services — primary care and specialty services — in one location near their homes.

"We know that convenience matters for patients," Boutros said. "They would like to do the least amount of travel between themselves and the health care organization. The closer you are, the more likely you are to have a closer relationship with them."