A large U.S. study found that giving patients increased levels of oxygen during surgery was associated with an increased risk of subsequent damage to the kidneys, heart, and lungs.
While the absolute risk remains low, this study suggests it’s time to reconsider the free use of oxygen during general anesthesia, the researchers say.
Oxygen is regularly given to nearly all patients undergoing surgery under general anesthesia to prevent hypoxia (dangerously low oxygen levels), and the World Health Organization recommends free use of oxygen to reduce the risk of infection.
During surgery, arterial oxygen saturation (SpO2) is continuously measured, allowing doctors to adjust the oxygen dose to the target level. Normal SpO2 is 94-95%. Giving too much oxygen to saturate hemoglobin, known as supraphysical oxygen, is common.
Superphysiological oxygen can harm the cells and tissues of the body, but the clinical significance of these effects during surgery remains uncertain, and previous tests have failed to detect any significant effect on organs.
To fill this gap in knowledge, a group of American researchers studied whether the administration of superphysical oxygen during surgery was associated with a decrease or increase in injuries to the kidneys, heart, and lungs after surgery.
Their findings are based on more than 350,000 patients (mean age 59 years, 52% female, 70% white) who underwent surgery using general anesthesia and tracheal intubation (a breathing tube placed in the windpipe) over 42 years. United States between January 2016 and November 2018.
Background information was collected on factors such as age, gender, ethnicity, weight (BMI), and medical history, and researchers tested patients for kidney, heart, and lung damage before and after surgery.
The researchers then used an algorithm to calculate the amount of oxygen delivered above air level (21%) compared to the time spent at 92% or higher oxygen saturation during surgery.
Medical records were used to track cases of acute kidney, heart, and lung injuries, as well as 30-day deaths, hospital stays, and strokes.
The average duration of the operation was 205 minutes. Acute kidney injury was diagnosed in 6.5% of patients, myocardial injury in 2.8%, lung injury in 4.4% after surgery.
After controlling for baseline factors and other potentially influencing variables, increased oxygen exposure during surgery was associated with an increased risk of organ damage.
Patients who received higher concentrations of oxygen (75%) had a 26% greater risk of acute kidney injury, a 12% greater risk of myocardial injury, and a 14% greater risk of lung injury than patients who received lower concentrations of oxygen (25%) .
Patients exposed to higher concentrations of oxygen also had a 9% higher risk of stroke and a 6% higher risk of death within 30 days of the procedure compared to patients exposed to lower concentrations (25%).
However, in patients with higher concentrations, the duration of hospital stay was somewhat shorter compared to patients exposed to lower concentrations, and this effect did not change after exclusion of patients who died before discharge.
These are observational findings, so the cause cannot be determined. The researchers acknowledge that not all patients were screened for kidney and heart damage after surgery, nor were they able to take into account factors such as diet, lifestyle, and medication that may affect susceptibility.
However, this was a large study conducted among geographically diverse populations, which ensures the accuracy and generalizability of the results. The results were similar after additional analyses, providing more confidence in their findings.
Based on their findings, the investigators say, “A large clinical trial is needed to detect a small but clinically meaningful effect on organ damage and patient-centered outcomes to guide intraoperative oxygen administration.”
Source: Medical Express