Study: Too much oxygen during surgery may harm kidneys, hearts and lungs

Nov. 30 (UPI) -- Patients who receive high levels of oxygen during surgery may have a greater risk of subsequent kidney, heart and lung injury, according to a large U.S. study published Wednesday in The British Medical Journal.

And even though the absolute risk of injury in this way remains low, the study's findings suggest it is "time to reconsider the liberal use of oxygen during general anesthesia," an accompanying editorial in the journal said.

Yet, Dr. Michael W. Champeau, president of the American Society of Anesthesiologists, told UPI that he doesn't think people undergoing surgery should be unduly concerned.

"In general, anesthesiologists try to tailor each anesthetic to the patient's needs, and most patients do extremely well. But, patients with multiple other serious medical problems have a higher risk of problems after their surgery," he said in an email.

According to the Vanderbilt University-led research team, oxygen is given routinely to almost all patients who undergo surgery with general anesthesia to help prevent a dangerously low oxygen level -- a condition called hypoxia.

In their paper, the investigators describe the administration of supplemental oxygen as "a foundational component of anesthesia," done to reduce tissue injury, lower the risk of surgical site infection and improve healing.

Dr. David R McIlroy, an anesthesiologist affiliated with Vanderbilt University Medical Center, is the study's primary author.

The researchers explained that arterial blood hemoglobin oxygen saturation, or SpO2, is continuously measured during surgery, enabling doctors to adjust the dose of oxygen to a target level.

While normal SpO2 is 94% to 95%, it is common practice to give oxygen in excess of what is required to saturate hemoglobin: known as supraphysiological oxygen.

It is this excess level of oxygen that can harm the body's cells and tissues, but the researchers said clinical evidence of such harm is limited.

So, they set out to analyze data for 350,000-plus adult patients, averaging 59 years old, who underwent surgery at least two hours long with general anesthesia and endotracheal intubation -- a breathing tube placed into the windpipe -- and were admitted to one of 42 U.S. medical centers after surgery between 2016 and 2018.

Acute kidney injury was diagnosed in 6.5% of patients, myocardial injury in 2.8% and lung injury in 4.4% after surgery.

Yet, patients at the upper end of oxygen levels had 26% greater odds of acute kidney injury, 12% greater odds of myocardial injury and 14% greater odds of lung injury, compared with patients at the lower end.

Patients at the upper end of oxygen levels also had 9% greater odds of stroke and 6% greater odds of death within 30 days after surgery than patients at the lower end. But they had a slightly shorter length of hospital stay versus patients who received less oxygen.

Champeau noted the study's observational design doesn't make it possible to say the higher levels of oxygen actually caused the damage to the heart, lungs and kidneys.

"Another possible explanation is that patients had other problems that caused the physicians to administer more oxygen and that those problems also led to the increase in organ damage," said Champeau, adjunct clinical professor of anesthesiology, perioperative and pain medicine at Stanford University School of Medicine in Palo Alto, Calif.

He added: "We already know that there are certain patients who can be harmed by excessive oxygen, and many anesthesiologists, including myself, already routinely limit the use of oxygen."

But, he said, the study will "put the issue on anesthesiologists' radar" and may lead to further overall reductions in the use of oxygen for the most vulnerable patients.

The researchers said they found no consistent evidence that the association between excess levels of oxygen and organ injury differed according to age, sex, race or type of surgical procedure.

In fact, the association was greatest in shorter procedures, they noted.

Factors such as diet, lifestyle and medication use, which can influence how susceptible a person is to organ injury, weren't considered for this research, the investigators said.

But they noted it was a large study, drawn from geographically diverse populations, and findings were similar after additional analyses.

They urged further research that includes measuring cognitive impairment.