Increased oxygen exposure during surgery ups risk of kidney, heart, lung injuries

Increased intraoperative exposure to oxygen appears to heighten the incidence of renal, cardiac, and pulmonary injuries, according to the results of an observational cohort study, noting that residual confounding of these associations cannot be excluded.

“In a large, heterogeneous, and contemporary cohort of patients undergoing a wide range of surgical procedures requiring general anaesthesia, the incidence of postoperative acute kidney injury (AKI), myocardial injury, and lung injury was each higher in patients exposed to increased supraphysiological oxygen administration during surgery,” the researchers said.

This study was conducted in 42 medical centres across the US, including 350,647 adult patients undergoing surgical procedures ≥120 minutes’ duration with general anaesthesia and endotracheal intubation who were admitted to hospital after surgery between January 2016 and November 2018.

Participants underwent supraphysiological oxygen administration, defined as the area under the curve (AUC) of the fraction of inspired oxygen above air (21 percent) during minutes when the haemoglobin oxygen saturation was greater than 92 percent.

Of the eligible patients (median age 58 years), 180,546 (51.5 percent) were women, and the median duration of their surgery was 205 minutes. AKI was diagnosed in 19,207 of 297,554 patients (6.5 percent), myocardial injury in 8,972 of 320,527 (2.8 percent), and lung injury in 13,312 of 312,161 (4.4 percent). [BMJ 2022;379:e070941]

The median fraction of inspired oxygen was 54.0 percent, while the AUC of supraphysiological inspired oxygen was 7,951 percent min. For instance, this was equivalent to an 80-percent fraction of inspired oxygen throughout a 135-min procedure.

Increased oxygen exposure correlated with higher risks of AKI, myocardial injury, and lung injury after accounting for baseline covariates and other potential confounding variables.

Compared to patients at the 25th centile, those at the 75th centile for the AUC of the fraction of inspired oxygen were 26 percent more likely to develop AKI (95 percent confidence interval [CI], 22‒30), 12 percent more likely to have myocardial injury (95 percent CI, 7‒17), and 14 percent more likely to experience lung injury (95 percent CI, 12‒16).

These findings were consistent in sensitivity analyses examining alternative definitions of exposure, in a restricted cohort, and in an instrumental variable analysis.

“Although supplemental oxygen is routinely administered to almost all patients during surgery, the best practice for intraoperative oxygen administration remains unknown,” the researchers said. “Few definitive and generalizable clinical trials powered to detect reasonable effect sizes have tested the effect of avoiding excess oxygen intraoperatively.”

A study by McGuinness and colleagues in 298 patients who underwent cardiac surgery found no effect on AKI from targeting intraoperative oxygen administration to achieve a partial pressure of oxygen of 75‒90 mm Hg relative to usual oxygenation strategies. [Anesthesiology 2016;125:465-473]

Likewise, findings from the study of Shaefi and colleagues in 100 patients undergoing cardiac surgery revealed no effect of intraoperative oxygen exposure on postoperative cognitive function or on renal failure, stroke, pneumonia, atrial fibrillation, or death. However, the study was underpowered for most of these events. [Anesthesiology 2021;134:189-201]

“A large clinical trial to detect small but clinically significant effects on organ injury and patient centred outcomes is needed to guide oxygen administration during surgery,” the researchers said.