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January 20, 2000

More oxygen also cuts post-op nausea, UCSF-led team says

Even as biotechnology promises to revolutionize medicine with lasers, gene chips and custom drugs, doctors are discovering that there are still cheap and simple ways to dramatically improve outcomes for many patients.

In the latest study, being published Thursday in the New England Journal of Medicine, researchers found that turning up the dial on the oxygen tank while patients are under anesthesia can halve the rate of post-operative infections.

An earlier study by the same group of researchers, led by a UC-San Francisco professor, found that upping the oxygen also halved the incidence of post-operative nausea and vomiting. And a few years ago, they showed that by keeping patients at a normal body temperature during surgery reduced infections three-fold, prompting widespread adoption of the practice.

Post-operative infections are a serious and fairly frequent complication for surgery patients, leading to longer hospital stays and sometimes death. And nausea is the leading complaint of surgery patients. It often prompts longer hospital stays, according to UCSF’s Daniel Sessler, professor of anesthesia and senior author of the latest study.

Of 250 colorectal surgery patients randomly chosen to receive an 80 percent concentration of oxygen, just 13 later developed infections. That compared with 28 infections among a control group of the same size that received a 30 percent concentration, the current standard.

Fewer deaths

Six patients in the control group died within 15 days of surgery, compared to one death in the experimental group. “Nobody appreciated that what we were doing in anesthesia was connected to infection,” said Sessler, noting that by the time problems showed up, anesthesiologists were no longer in contact with the patient.

Sessler is director of the Outcomes Research Group, a confederation of 70 scientists in the United States and abroad who are looking at fairly simple steps that may have a significant impact on patients. He analyzed the data, most of which was collected from patients in Austria and Germany.

Earlier work by Sessler and the Outcomes group also showed a dramatic decrease in infections by keeping patients at normal body temperature with a quilt covering filled with warm air. It is now part of standard operating room procedure.

The results regarding oxygen are very new and have not yet caught on, but an editorial in the journal by Danish doctor Finn Gottrup said the findings warrant adoption, at least in colorectal surgery.

Surprise to anesthesiologists

The findings will be a surprise to many anesthesiologists, even though Sessler said past physiology studies have shown that increasing oxygen would likely reduce infections.

William Hetrick, chairman of the committee on surgical anesthesia for the American Society of Anesthesiologists, said he was not even aware of the reported benefits of oxygen, although he said Sessler is well-regarded in the field.

Sessler’s colleague, UCSF professor emeritus John W. Severinghaus, had not seen the study, but said that unless the results are refuted by other research, the study “will shake things up a lot.” “You don’t need any new equipment,” Severinghaus said. “It’s just a matter of practice change.”

Sessler said doctors feared giving patients higher concentrations of oxygen because it is known that people with severe breathing problems developed lung damage after being given oxygen-saturated air for several days.

Short-term exposure

But Sessler said his group showed that exposure during the few hours a patient is under anesthesia isn’t enough to cause problems. Instead, patients need the extra oxygen to help their bodies battle bacteria. Immune cells called neutrophils can kill invaders by exposing them to a highly reactive form of oxygen — the same molecules known as “free radicals” that over a person’s lifetime damage cells and contribute to aging.

Sessler doesn’t know why oxygen also cuts post-operative nausea. He suspects it is because the colon and intestines often have their blood supply diminished during surgery, and that may trigger a release of serotonin, a neurotransmitter known to be linked to nausea. But if the blood those organs receive has more oxygen, it could lessen the chance of a reaction, he said.

As for keeping patients warm, the result is to relax blood vessels and allow more blood and immune cells to circulate to the tissues where bacteria get a foothold. But it wasn’t until 12 years ago that a doctor came up with an inexpensive and fairly easy way to keep patients at a normal body temperature without forcing everyone in the operating room to work in a super-heated environment.