U.S. hospital admissions in November were the weakest in more than a decade, under pressure from a change in reimbursement rules for Medicare patients and confusion tied to the problem-ridden rollout of Obamacare, according to a survey by Citi Research. New billing rules for the Medicare program for the elderly and disabled require hospitals to treat patient stays lasting less than "two midnights" as an outpatient visit. "In addition, it is reasonable to conclude that the cumulative impact of changing physician employment and payment models is beginning to play a role, as well as the paralyzing effect of the impotent Obamacare rollout," Citi analyst Gary Taylor said in a report.