Higher levels of excess oxygen given to patients under general anesthesia add risk of injury to the kidneys, lungs and heart, according to a large observational study led by researchers at Vanderbilt University Medical Center, reported Nov. 30 in The BMJ, the flagship journal of the British Medical Association.
The study used data from 350,647 adult patients who underwent major surgery at 42 U.S. medical centers from January 2016 to November 2018.
“Supplemental oxygen is administered to patients during surgery to limit risk and improve outcomes, but this study highlights potential harm of excess oxygen administration,” said Frederic (Josh) Billings IV, MD, MSc, associate professor of Anesthesiology and Medicine, who led the study with David McIlroy, MD, associate professor of Anesthesiology. “A large, definitive clinical trial to detect small but clinically significant effects of different oxygen administration strategies would be a next step toward addressing this vital and nagging issue.”
In an editorial linked to the report, experts said the study suggests it’s time to reconsider liberal use of oxygen during general anesthesia.
Oxygen accounts for 21% of room air. But for patients under general anesthesia, in air delivered to lungs by mechanical ventilation, anesthesiologists administer oxygen concentrations far in excess of 21%. Depending on the patient and the procedure, 40 to 100% might figure as a typical range.
The best concentration remains in question.
The researchers ranked all 350,647 patients according to intensity and duration of excess oxygen received, those at the top having gotten oxygen exposures around four times that of those at the bottom. (The study defined excess oxygen as ventilator oxygen concentrations greater than 21%. Concentrations delivered during any period when a patient’s arterial hemoglobin oxygen saturation was below 93% were not counted as excess oxygen.)
After data were adjusted for potential confounders, compared to patients down in the 25th centile of excess oxygen exposure, those in the 75th centile had 26% greater odds of acute kidney injury, 14% greater odds of lung injury, and 12% greater odds of myocardial injury, which often presents as silent or overt heart attack.
(Background rates of these injuries across the patient group as a whole were 6.5%, 4.4% and 2.8%, respectively.)
Among the study’s secondary outcomes, compared to those in the 25th centile, patients in the 75th centile of excess oxygen exposure had 9% greater odds of stroke and 6% greater odds of 30-day mortality.
Data for the study came from medical centers participating in the Multicenter Perioperative Outcomes Group, which is based at the University of Michigan in Ann Arbor.
Others on the study from VUMC include Matthew Shotwell, PhD, Marcos Lopez, MD, Cassandra Hennessy, MS, Jonathan Wanderer, MD, MPhil, Matthew Semler, MD, MSCI, and Todd Rice, MD, MSc. They collaborated with researchers from the University of Michigan and Oregon Health and Science University in Portland.
The study was supported by the National Institutes of Health (GM112871) and the Association of University Anesthesiologists.
