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NEW ORLEANS -- There was no benefit to giving patients supplemental oxygen during surgery to reduce postoperative nausea and vomiting (PONV), according to a post hoc analysis of a randomized trial.

The multiple cross-over cluster trial had eight isolated operating rooms randomized to alternate between 80% versus 30% fractions of inspired oxygen every 2 weeks for 3 years. During the periods of 80% intraoperative oxygen, there was no improvement in PONV during the first 24 hours after noncardiac surgery, reported David Sessler, MD, of the Cleveland Clinic.

Between 80% and 30% inspired oxygen, there is "absolutely no difference whatsoever. This [trial] is not underpowered. This is as negative as you can get," he said in a presentation at the American Society of Anesthesiologists (ASA) annual meeting. An ASA session moderator noted that the manuscript has been accepted for publication in Anesthesiology.

PONV is one of the most common complications of surgery, with an incidence of approximately 30% in the general population. Guidelines suggest that all patients should receive PONV prophylaxis during the perioperative period. Clinicians are less perioperative opioids, opt for regional anesthesia and propofol infusion instead, avoid volatile anesthetics, and maintain adequate hydration in patients undergoing same-day surgery.

In theory, supplemental intraoperative oxygen should be of help because hypoxia is thought to promote PONV: surgery is physiologically stressful, and cells with high metabolic demands tolerate hypoxia poorly.

Yet Sessler's group found no difference not only in PONV, but other outcomes such as:

• Time to initial antiemetic administration
• Number of antiemetic doses
• Patient-reported PONV severity in the post-anesthesiology care unit

Results were consistent when the study was included in a meta-analysis comprising 10 trials with 6,773 patients in total. Altogether, there was no beneficial effect of supplemental oxygen on PONV (RR 0.97, 95% CI 0.86-1.08) or antiemetic doses (RR 0.92, 95% CI 0.79-1.09), Sessler noted.

His group had performed a post hoc subanalysis of an that had found supplemental oxygen to be of no help for preventing infections after major intestinal surgery. Other research has shown that 80% oxygen does not reduce atelectasis, pulmonary complications, or long-term mortality.

"We therefore conclude that any oxygen fraction between 30% and 80% is fine. Use whatever you want," Sessler stated.

Study patients were adults having colorectal surgery at least 2 hours with general endotracheal anesthesia who spent at least one night in the hospital. Of the 5,749 individuals , the 5,167 who had sufficient PONV data were included in the present analysis.

The cohort averaged age 52, with about half being men. Surgeries lasted on average 4 hours, and the majority of patients had Apfel risk scores of 2 or 3.

Only about 3% of participants received preoperative antiemetics, whereas nearly all got them intraoperatively. Nearly all received postoperative opioids as well.

Sessler cautioned that the study did not have a randomized design, which left room for bias. In addition, certain PONV variables, such as number of episodes, were lacking in the dataset.

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