Use of anesthesiologists to monitor sedation during colonoscopies and other digestive imaging tests has more than doubled in recent years, and they're used most often for low-risk patients who typically don't need the extra help, the study authors said.

"These services are not harming patients. They're basically giving them a luxury that is not strictly necessary," said the study's lead author, Dr. Soeren Mattke, a senior Rand Corp. scientist. That matters at a time when policymakers are trying to rein in rising medical costs, the authors said.

Patients usually are briefly sedated for a colonoscopy, and some kinds of sedation require monitoring by specialists. That includes use of propofol, a powerful intravenous drug that can cause deep sedation and was implicated in pop star Michael Jackson's death. Anesthesiologist-monitored sedation, with or without propofol, is recommended for high-risk patients, including those who are old or sick or previously had complications with anesthesia.