Reducing the use of climate-warming inhaled gases can cut emissions associated with surgical anesthesia in half, according to a new analysis. What’s more, the study found no impact on patient safety or comfort associated with the changes.
About 3% of greenhouse gas emissions in the health care system come from anesthesia—specifically, inhaled gases such as nitrous oxide (which has a warming effect 270 times more potent than carbon dioxide) and fluorinated ethers.
Researchers have begun exploring ways to reduce emissions from anesthesia, such as by using regional rather than general anesthesia where possible or choosing less harmful anesthetic gases (different fluorinated ethers vary in climate impact by up to 50-fold). The University of Michigan medical system got in on this effort with their Green Anesthesia Initiative (GAIA) launched in March 2022.
The initiative aimed to reduce the use of nitrous oxide, stimulate a shift to less harmful inhaled fluorinated ethers, and increase the use of intravenous anesthetics. Hospital administrators and clinical leaders made the case for these changes through written communications and in-person meetings, equipment compatible with the use of sevoflurane (the least climate-damaging inhaled agent) was rolled out across the health system, and desflurane (the worst global warming offender) was removed from the formulary.
In the new study, researchers analyzed data on nearly 93,000 surgical patients across the University of Michigan medical system treated between March 1, 2021 and February 28, 2023—a total of 45,692 patients in the year before the GAIA Initiative launch and 47,199 in the year afterwards. The researchers tracked the climate impact of surgeries, the amount of anesthetic used, and patient outcomes including nausea and vomiting after surgery, pain scores, and awareness during anesthesia.
The climate impact of each surgical case was reduced by the equivalent of more than 14 kg of carbon dioxide on average, the researchers report in the journal Lancet Planetary Health. “Across the 1-year intervention period at a single institution, we halved CO₂ emissions during anaesthesia maintenance, which equates to 2·7 million km (1·7 million miles) driven by a standard passenger car,” the researchers write.
There were no changes in the depth of anesthesia, pain scores, postoperative nausea and vomiting, or the risk of intraoperative awareness. “The study shows that it is possible for practice changes to markedly decrease the environmental impact of administering anesthesia without impacting patient safety or outcomes,” says study team member Douglas Colquhoun, assistant professor of anesthesiology at the University of Michigan.
“These improved environmental impact outcomes are consistent with prior work, but crucially, prior work had not quantified any impact on patient outcomes,” Colquhoun says. “While not unexpected, we were reassured to find no change in patient outcomes.”
The use of relatively climate-friendly sevoflurane increased from 44.1% of cases to 68.2% after the launch of GAIA. The use of intravenous propofol did not change (sitting at about 40% of cases both pre- and post-GAIA). Nor was there any difference in the amount of anesthetic used, suggesting that the decrease in the climate impact of surgery was primarily due to changes in the choice of anesthetic gases.
Use of nitrous oxide declined from 58.3% of cases to 28.9% of cases after the launch of GAIA. Institutions that use a lot of nitrous oxide often distribute the gas via pipeline systems that are notoriously leaky, magnifying the climate impact. The reduction in nitrous oxide use enabled the University of Michigan medical system to decommission its pipeline in favor of a more environmentally friendly setup with nitrous oxide cylinders attached directly to anesthesia machines.
Another strategy to cut emissions from anesthesia is to reduce the rate at which fresh gas is added to the anesthesia mix. This strategy has sometimes been portrayed in the media as reducing the dose of anesthesia and putting patients at risk of harm, but the researchers say this is not accurate. The University of Michigan health system is currently implementing technology that is widely used in Europe to reduce fresh gas flow, and this could achieve an additional emissions savings of perhaps 30%, the researchers write.
“Additionally, we need to continue to carefully evaluate the impact of perioperative care generally,” says Colquhoun. “Operating rooms are resource intensive and large amounts of waste can be created by a single procedure.”
Source: Colquhoun D.A. et al. “Environmental and patient safety outcomes of a health-system Green Anesthesia Initiative (GAIA): a retrospective observational cohort study.” Lancet Planetary Health 2025.
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