By DAN FROSCH

The debate pits nurse anesthetists, who specialize in administering anesthesia and maintain that they are well equipped to treat patients on their own, against anesthesiologists, who are physicians and say nurses lack the necessary training.

The dispute dates to a 2001 change in Medicare and Medicaid regulations, allowing states to opt out of a requirement that nurse anesthetists be supervised. And it is part of a broader turf war over how much power nurses should have in treating patients.

“With the removal of the requirement, it actually increases access to health care for citizens in rural Colorado,” said Scott K. Shaffer, president of the nurse anesthetists association in Colorado, one of 17 states that have chosen to allow nurses to deliver anesthesia without supervision.

Since Colorado’s rural hospitals were exempted from the supervision regulation in 2010, Mr. Shaffer said, some medical facilities that may not have employed anesthesiologists have been able to attract specialists because there is no longer a concern about who would administer anesthesia or supervise.

“Now patients don’t have to turn around and go to Colorado Springs or Denver when they can be taken care of in their hometown,” he said.

In Colorado, however, the issue has prompted a legal battle. In 2010, anesthesiologist and medical societies filed a lawsuit in state court asserting that allowing nurse anesthetists to deliver anesthesia without supervision was not consistent with state law, a requirement for opting out of the federal rule.

But a judge dismissed the case, ruling that the legislature had indeed intended for the practice to be permitted. The medical groups appealed last May.

“There is a very different background between nurses and physicians in both education and training,” said Dr. Randall Clark, a spokesman for the Colorado Society of Anesthesiologists. “Anesthesia is a very complex and technically demanding area of medicine that, at its core, needs to be either performed by a physician or supervised by one.”

Dr. Clark said that despite concerns about health care access, his group believed that there were more anesthesiologists than nurse anesthetists currently working in the nearly 50 rural Colorado hospitals affected by the opt-out decision. And in those instances when a hospital does not have a staff anesthesiologist, he said, it is still safer to have a physician on hand to supervise lest complications arise.

At a state appeals court hearing in Denver on Tuesday, Assistant Attorney General LeeAnn Morrill argued that Colorado law clearly permitted doctors to delegate medical functions to advanced practice nurses. Joseph J. Bronesky, a lawyer for the anesthesiologist society, said the law was murkier.

The case is being watched closely by national nursing and anesthesiologist groups, for whom the debate has become increasingly contentious. Each side has promoted studies backing its perspective.

The American Society of Anesthesiologists cited a 2000 study financed by the federal Agency for Healthcare Research and Quality, which found that the presence of an anesthesiologist helped prevent deaths in cases where an anesthesia or surgical complication had occurred.

Conversely, the American Association of Nurse Anesthetists referred to a study it financed that was published in Health Affairs in 2010. It examined Medicare data from 1999 to 2005 and found no evidence that opting out of the supervision requirement resulted in increased inpatient deaths or complications.

“When it comes to giving anesthesia, certified registered nurse anesthetists and anesthesiologists are identical,” said Christopher Bettin, a spokesman for the nurse anesthetists group. “There are no differences in what they learn, the drugs and equipment they use and the standards of care they follow.”

Colorado is not the only state where the dispute over nurse anesthetists has ended up in the courts. Last month, the California Society of Anesthesiologists petitioned the State Supreme Court to review its lawsuit over California’s 2009 decision to opt out of the supervision requirement. The group’s suit, initially filed in 2010, has so far been unsuccessful.

“Our concern is patient safety,” said Dr. Kenneth Y. Pauker, president of the California group. “Is an independent nurse able to tender the same quality of care as an anesthesiologist or an anesthesia care team? What happens when things get really complex and you have to call upon all your years of medicine?”

Jana Du Bois, chief counsel for the California Hospital Association — which has sided with the nurses, as has its Colorado counterpart — said that rural areas in California continued to struggle to recruit and retain specialists.

“If there aren’t enough physicians and a woman in labor comes in, you can’t say, ‘We have to wait until next week to get an anesthesiologist,’ ” she said.