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November 9, 1999 By NANCY BETH JACKSON

Patients often wake up from general anesthesia with nausea and vomiting, but researchers say they can sharply reduce the incidence of these symptoms with a relatively simple step: increasing the amount of oxygen given to surgery patients.

The reductions are especially important now that many patients who might once have stayed in the hospital after surgery are treated as outpatients.

In the atmosphere, air has almost four times as much nitrogen as oxygen, and surgery patients usually are given 30 percent oxygen and 70 percent nitrogen; the mix is richer in oxygen than regular air because patients breathe less efficiently during surgery. But in a double-blind random study of 231 patients at two Vienna hospitals, Dr. Daniel Sessler, a professor at the University of California in San Francisco, and his colleagues found that the frequent side effects of general anesthesia could be diminished by giving patients even more oxygen: a mix of 80 percent oxygen and 20 percent nitrogen during the surgery and for two hours afterward. Only 17 percent of the patients receiving supplemental oxygen experienced nausea and vomiting, compared with 30 percent of the group who were given the usual amount.

“The mechanism remains unclear,” Sessler said, but he added, “The take-home message from the new studies is that extra oxygen is cheap, risk-free and reduces the incidence of nausea as well as any known drug.”

The study, reported in the current issue of Anesthesiology, focused on patients, 18 to 80 years old, after elective colon surgery. A related study by members of Sessler’s team, published in the journal last month, indicated that patients given oxygen in amounts up to 80 percent did not suffer impaired lung function.

Nausea and vomiting can accompany other types of surgery, including abdominal surgeries and procedures involving the middle ear and the eye. As many as seven people in 10 experience these side effects after general anesthesia, Sessler said.

Dr. Gary R. Haynes, an anesthesiologist at Medical University of South Carolina who has studied the side effects, notes that children, adolescents and pregnant women are particularly affected.

Dealing with post-operative nausea and vomiting has become a critical issue for anesthesiologists as outpatient surgery has increased in recent years. Beyond the question of patient comfort is concern for complications like pneumonia, dehydration and retching that can open sutures, leading to infection. And even a few extra hours in an outpatient clinic can increase the cost of surgery. In addition, the symptoms may occur after the patient has left the clinic, Haynes said.

Dr. Jeffrey L. Apfelbaum, vice chairman for anesthesiology and critical-care medicine at the University of Chicago, said the study was “excellent” but urged caution because of its size and because the problems are caused by “a lot of different things.”

The study was paid for by the National Institutes of Health, the Joseph Drown Foundation and several Austrian grants.