The incidence of nausea -- a frequent side effect of general anesthesia -- can be dramatically reduced simply by giving patients more oxygen during and after surgery, according to a new study led by University of California, San Francisco scientists.
The study, reported in the November issue of the journal Anesthesiology, found that the use of increased oxygen provides a simple, effective way to cut in half the number of patients who experience nausea.
A companion study led by UCSF researchers and reported in the October issue of the journal confirmed the safety of the procedure. Both studies involved researchers at UCSF and in Vienna.
As many as seven people out of ten experience nausea or vomiting after general anesthesia, said Daniel Sessler, MD, professor of anesthesia and perioperative care at UCSF and senior author of both studies.
The most effective anti-nausea drugs cost $30 per dose, he said, and are not given routinely but only after patients become sick to their stomachs. The drugs have only a fifty-fifty chance of working, he added.
In contrast, the use of additional oxygen costs almost nothing, causes no known problems, and can be given to all patients from the outset of surgery.
"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," Sessler said.
In the new study, the researchers examined the effect of using 80 percent oxygen in the gas mixture administered during anesthesia compared with the standard 30 percent oxygen. In both cases, the designated oxygen level was maintained for two hours after surgery.
The study focused on 231 patients undergoing colon surgery at two hospitals in Vienna -- Donauspital-SMZO and the Vienna General Hospital. About half received the conventional 30 percent oxygen in their anesthesia gas and for two hours during recovery, and the other half received the elevated, experimental, oxygen levels during these periods.
Although the research shows that the extra oxygen is safe and effective, the scientists do not yet know why it decreases nausea. One possibility suggested in their paper is the fact that during abdominal surgery the intestines do not get the usual amount of oxygen, due to surgical cutting or temporary displacement of organs to facilitate surgery. Tissues are known to react to an inadequate oxygen supply by releasing neurotransmitters and other potent chemical messengers that in turn cause nausea and vomiting. This is thought to be a reaction evolved to rid the body of possibly life-threatening, noxious food.
In other words, many surgical patients have an unconscious gut reaction to what is happening in their intestines, and their evolved response is nausea and vomiting to rid the stomach of the source of the problem.
"The extra oxygen may help the tissue avoid this reaction," Sessler suggests. The research is part of on-going studies by an international science team, the Outcomes Research Group, examining accepted practice in anesthesiology to determine if simple improvements can produce major benefits. Several years ago, Sessler and colleagues determined that keeping patients' bodies warmer than had been the custom cut the rate of post-operative infections three-fold. General anesthesia was known to lower a patient's temperature by about two degrees Fahrenheit, but no one had examined the down-side of the body's natural reaction to general anesthesia. Simply warming patients can maintain normal temperature, Sessler noted, and this has now become standard practice during general anesthesia.
This summer, the research group reported finding that patients with poorly controlled post-surgical pain had higher risk of infection than did those whose pain was better controlled, perhaps because pain reduces the oxygen supply available to tissues, which in turn can limit the body's ability to fight infection.
Studies continue on other links between anesthesia conditions and patients' outcomes.
Lead author on the supplemental oxygen paper is Robert Greif, MD, research fellow in anesthesia and perioperative care at UCSF. Co-authors are Sonja Laciny, MD, also a UCSF research fellow; Brigitta Rapf, MD, attending physician in anesthesiology and intensive care medicine at Donauspital-SMZO, Vienna, Austria; and Randy Hickle, MD, chief executive officer of Apotheus Laboratories, Lubbock Texas.
The research was funded by the National Institutes of Health, the Joseph Drown Foundation, and several Austrian grants.
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