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Medpage Today, October 2005

October 3, 2005

VALENCIA, Spain, Oct. 26 – The third study on more or less inspired oxygen to prevent wound infections has broken the tie. It tipped the scales toward more oxygen.

The first study concluded that 80% oxygen during colorectal surgery halved the rate of wound infections compared with those who received 30% supplemental oxygen. It was published in 2000 in the New England Journal of Medicine by a team in Vienna.

The second study, with general surgery patients, had diametrically opposed results. It was published in 2004 in the Journal of the American Medical Association by a team from Weill Cornell Medical College in New York.

Now a randomized, double-blind study of adults undergoing open colorectal surgery procedures at 14 Spanish hospitals found that patients who received 80% supplemental oxygen during surgery and for six hours afterward had a 39% lower risk of surgical site infections compared with those who received 30% oxygen.

The investigators undertook the current trial to see whether they could figure out which of two studies with differing results was correct, according to anesthesiologist F. Javier Belda, M.D. of the University Clinical Hospital here and colleagues. The study results were published in the Oct. 26 issue of Journal of the American Medical Association.

To determine whether a higher fraction of inspired FIO2 was good, bad or indifferent, Dr. Belda and colleagues at the 14 Spanish centers studied adults between the ages of 18 and 80 years who underwent elective, non-laparoscopic colorectal resection procedures.

The patients were randomly assigned to 30% or 80% FIO2 during and for six hours after surgery. Anesthesia and antibiotic administration were standardized, and surgical wounds infections were diagnosed by investigators blinded to patient status, using criteria from the U.S. Centers for Disease Control and Prevention.

The primary study outcome was any surgical site infection. Secondary outcomes were return of bowel function and ability to tolerate solid food, time to ambulation and suture removal, and duration of hospitalization.

Infections occurred in 35 of the 143 patients (24.4%) who received 30% perioperative oxygen, compared with 22 of the 148 patients (14.9%) who breathed in 80% oxygen during and shortly after surgery.

Patients who received 80% FIO2 had a 39% lower risk of wound infection (relative risk 0.61; 95% confidence interval, 0.38-0.98, P =.04).

When the data were adjusted for variables such as age, weight, gender, co-existing allergy, respiratory disease, or smoking status, only FIO2 and respiratory disease were significantly associated with the risk of infection. After adjustment, patients in the 80% oxygen group had a relative risk of 0.46 (95% CI, 0.22- 0.95; P = .04) compared with those in the 30% group.

Patients with coexisting respiratory disease had a 3.23-fold greater risk for surgical site infection, the investigators determined.

There were no significant differences between the groups in any of the secondary outcomes, the authors noted.

“All surgical wounds become contaminated to some degree,” Dr, Belda and colleagues wrote. “The primary determinant of whether contamination is established as a clinical infection is host defense. Host defense is most critical during a decisive period lasting a few hours after contamination. For example, antibiotics ameliorate infections and hypoperfusion aggravates infections only during the first few hours after contamination.”

They noted that the optimal duration of supplemental oxygen administration is unknown, but given the similar results between the Spanish and Austrian studies, giving 80% FIO2 for two hours after surgery may be sufficient to provide protection against wound infection, they suggested.

The findings, if confirmed, could have important implications, wrote E. Patchen Dellinger, M.D., a professor and chief of the division of general surgery at the University of Washington in Seattle, in an accompanying editorial.

“For instance, with an estimated 600,000 surgical-site infections per year for major surgery in the United States alone, at an estimated cost of $1.8 billion, a 39% reduction would represent a dramatic improvement in terms of reducing both morbidity and cost,” Dr. Dellinger wrote.

Although the question of the ultimate benefit or detriment of supplemental perioperative oxygen may not be answered until larger clinical trials can be performed, “surgeons should not wait for this issue to be resolved before moving forward with this simple, inexpensive, and low-risk intervention while at the same time monitoring both its effectiveness in the community at large and the chance that its use will have unintended consequences,” Dr. Dellinger commented.

The 2000 Austrian study, led by anesthesiologist Robert Greif, M.D., of Vienna, found that patients who received 80% oxygen during colorectal surgery had half the rate of wound infections of those who received 30% supplemental oxygen.

“The perioperative administration of supplemental oxygen is a practical method of reducing the incidence of surgical-wound infections,” Dr, Greif and colleagues wrote.

Yet the second study, led by anesthesiologist Kane O. Pryor, M.D., of Weill Cornell Medical College in New York, found that in a general surgery population the risk of infection among those getting an 80% fraction of inspired oxygen (FIO2) was double that of patients who had gotten 35% FIO2.

“The routine use of high perioperative FIO2 in a general surgical population does not reduce the overall incidence of SSI and may have predominantly deleterious effects,” those investigators wrote.