High concentrations of oxygen during anesthesia may increase risk of organ injury

Unnecessarily high concentrations of oxygen given to patients under general anesthesia may increase risk of injury to the kidneys, lungs and heart, according to a large Vanderbilt University Medical Center-led study published in The BMJ, the flagship journal of the British Medical Association.

Oxygen accounts for 21% of room air, but anesthesiologists typically administer it to patients through mechanical ventilation in concentrations between 40% and 100%, according to lead author Frederic (Josh) Billings IV, MD, MSc, associate professor of Anesthesiology and Medicine.

"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 Billings, who led the study with David McIlroy, MD, associate professor of Anesthesiology.

Study authors used data from 350,647 adult patients who underwent major surgery at 42 U.S. medical centers from January 2016 to November 2018, combining intensity and duration to quantify the total amount of excess oxygen received. Data came from medical centers participating in the Multicenter Perioperative Outcomes Group, which is based at the University of Michigan in Ann Arbor.

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. Some patients received close to four times the amount of excess oxygen as others.

The best concentration of oxygen for patients under anesthesia remains in question; more may not always be better. After data were adjusted for potential confounders, we found patients at the 75^th centile for excess oxygen administration had 26% greater odds of acute kidney injury, 14% greater odds of lung injury, and 12% greater odds of myocardial injury compared to patients at the 25th centile for excess oxygen administration."

David McIlroy, MD, Associate Professor of Anesthesiology

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 at the 25^th centile, patients at the 75^th centile of excess oxygen exposure had 9% greater odds of stroke and 6% greater odds of 30-day mortality.

McIlroy and Billings agree that these findings highlight the urgent need for a high-quality, large trial to better guide this fundamental aspect of anesthesia.

The study was supported by the National Institutes of Health (GM112871) and the Association of University Anesthesiologists.