Donald Berwick, MD, doesn't know what he'll be doing after Dec. 31. The Harvard pediatrician who runs the federal Centers for Medicare & Medicaid Services needs Senate approval by the end of the year, or he's out of a job. No confirmation hearings have been scheduled. Berwick, who met with editors and reporters at The Boston Globe Friday morning, said he doesn't think often about his future after Medicare, both because he's prohibited under ethics rules from interviewing for jobs and because his current work is so intense. "This is the best job I've ever had and the best job in American healthcare," he said. During his visit to the Globe, Berwick repeatedly hit on the theme of improving care and saving money by "making care coordinated, seamless, and scientifically-based." He spoke of curing the American health care system of its "addiction to volume" rather than to quality.