Almost two months after total knee replacement (TKR) dropped off Medicare’s inpatient-only (IPO) list, hospitals are building the architecture for patient-status decisions—and comorbidities seem to be at the heart of it. That makes sense because CMS emphasized comorbidities in the 2018 outpatient prospective payment system (OPPS) regulation that made this move, which will reduce reimbursement for many hospitals and challenge their compliance under the two-midnight rule. The presence of comorbidities, however, aren’t enough to justify inpatient admission, physician advisers say. They must complicate the treatment and put the patient at risk, even if they don’t always push the stay past two midnights.

“I am very guarded with the general thinking that comorbidities alone will be enough to justify inpatient status from the outset. They are an important factor to consider, but I’m doubtful that a patient with stable hypertension and Type 2 diabetes undergoing an uncomplicated procedure, having an uneventful post-op course and being discharged on day two will be accepted as inpatient on a quality improvement organization audit,” says Todd Butz, M.D., physician advisor at WellSpan Health in York, Pa. However, there are some “red-flag” comorbidities that will require inpatient admission for TKR because of the danger they pose to patients, he says.