The rate of infection from surgical wounds can be cut in half simply by giving patients more oxygen during and after anesthesia, according to a new study led by a University of California, San Francisco scientist.
The safe, inexpensive practice can save lives, time and money, the researchers report, since wound infections are common, often prolong hospitalization and can cause fatal complications. In colorectal surgery, for example, wound infection rates range from nine to 27 percent and often extend hospital stays a week or more, the scientists noted.
The dramatic finding of reduced infections with increased oxygen is based on a study of 500 patients who underwent colon surgery in three European hospitals. The report on the study appears in the January 20 issue of the New England Journal of Medicine.
The increased oxygen inhaled by patients during and after surgery appears to improve their immune system's ability to fight infections, the scientists found. Immune cells called neutrophils normally kill invading bacteria by exposing them to a highly reactive form of oxygen. This is the most important immunologic defense against bacteria associated with surgery, and research has shown that the number of bacteria killed is directly linked to the amount of oxygen in wound tissues. In the new paper, the scientists report that breathing extra oxygen markedly increases the amount of oxygen available to neutrophils.
"We now have evidence that increasing oxygen levels during and just after anesthesia provides the immune army with more ammunition to kill bacteria at the wound site," said Daniel Sessler, MD, professor of anesthesia and perioperative care at UCSF, senior author on the NEJM paper and director of the international Outcomes Research™ Group that carried out the study.
The collaboration between UC San Francisco and European investigators drew on patients at the Donauspital-SMZO in Vienna, the University of Vienna and the University Hospital Eppendorf in Hamburg, Germany. It is the latest of several hundred studies by the Outcomes Research � Group examining accepted practices in anesthesiology in search of simple, inexpensive ways to significantly improve anesthesia care.
Several years ago, the group determined that post-operative infection rates could be cut three-fold simply by keeping patients warmer during general surgery. The team also found this practice reduced blood loss and the need for transfusions. Maintaining patients' normal body temperatures during surgery has since been widely adopted.
Last year the group showed that increasing oxygen during and after anesthesia is safe and cuts the risk of postoperative nausea and vomiting in half.
In the current study, 500 patients undergoing surgery for colon cancer or inflammatory bowel disease were randomly assigned to breathe one of two oxygen concentrations during and for two hours after surgery. One group was given 30 percent oxygen as is routine; the other group received 80 percent oxygen. Both groups received identical amounts of anesthesia. Neither the surgeons nor surgical nurses were aware of which oxygen concentration their patients were receiving.
Using two different methods, the scientists measured the availability of oxygen to the patients' tissues. As might be expected, those breathing extra oxygen had more oxygen in their tissues. As a result, they had half as many wound infections as those who breathed the conventional 30 percent oxygen. Surgical wound infections developed in 28 of the 250 patients given 30 percent oxygen, but only in 13 of the 250 patients on the 80 percent oxygen regimen.
Six of the patients given conventional oxygen died within 15 days of surgery, while only one patient given 80 percent oxygen died. In all cases, the cause of death was overwhelming infection, the scientists reported. Though striking, the difference is not statistically significant, they noted.
Patients in the study who developed wound infections required an additional week of hospitalization, a result consistent with previous studies showing that wound infections cost an average of $12,500 per patient. In contrast, "Medical oxygen costs only a thousandth of a cent per quart," Sessler points out. "It is 40 times less expensive than tap water."
The researchers conclude that supplemental oxygen is safe and cuts the risk of surgical wound infection in half.
"The logical conclusion is that the standard oxygen concentration during surgery should be increased from 30 percent to 80 percent, Sessler said. Collaborators in the research with Sessler and co-authors on the NEJM paper are Robert Grief, MD, research fellow in anesthesia and perioperative care at UCSF; Ozan Akca, MD, research fellow, University of Vienna; Ernst-Peter Horn, MD, assistant professor of anesthesia at University Hospital Eppendorf; and Andrea Kurz, MD, assistant professor of anesthesia, Washington University, St. Louis.
The research was funded by the National Institutes of Health, the Fonds zur Forderung der wissenschaftlichen Forschung, the Joseph Drown Foundation, the Anesthesia Patient Safety Foundation, the Max Kade Foundation, the Erwin-Schrodinger Foundation, the Burgermeister Fond der Stadt Wien, and the Austrian National Bank Fond.
More information on the findings by the Outcomes Research™ Group can be found at http://or.org
Journal
New England Journal of Medicine