Researchers look to recover waste anaesthetics

A TEAM of chemical engineers and doctors are developing a new membrane to capture and reuse anaesthetic gas that is currently vented from hospitals.

Around 95% of the anaesthetic gas given to patients through anaesthetic machines is not metabolised. While the exhaled gas is captured within the hospital scavenging system it is typically vented to atmosphere and there are concerns about the environmental consequences.

A 2015 study reported that anaesthetic gases such as sevoflurane have global warming potentials 2–3 orders of magnitude higher than CO₂. A 2010 study estimated that the emissions of volatile anaesthetic agents worldwide are equivalent to the CO₂ emissions from 1m cars.

Chemical engineers from the University of Melbourne, Australia hope to alleviate the problem after their research showed a ceramic filter can recover sevoflurane for re-use while letting through smaller molecules like nitrogen, oxygen, water vapour and CO₂. The team created microporous organosilica membranes from 1,2-bis(triethoxysilyl)ethane (BTESE) using a sol-gel method followed by thermal processing.  

The team reports that the membrane would reduce the volume of sevoflurane from 2% by volume in the incoming feed to 0.04% in the permeate. The membrane performs well in the high-humidity conditions of the breathing circuit and because it is ceramic it is stable at high temperatures and could be sterilised using steam, as is common with other elements of anaesthetic machines.

“We’ve found a way to recover these gases, so they can be used by patients rather than disappearing into the atmosphere,” says researcher Sandra Kentish, Head of the School of Chemical and Biomedical Engineering at Melbourne. Kentish led the engineering side of the team along with her colleague Liang Liu.

The researchers propose retrofitting a membrane unit to existing machines. They are now looking for an industry partner to help develop a prototype. Kentish said the most challenging aspect will be finding a way to modify the exhaust system without interfering with the atmospheric pressure the patient experiences.

“We only need to modify the back end of the existing anaesthetic machine, which we think makes economic sense given the potential savings,” she says.

Environmental Science & Technology: https://doi.org/10.1021/acs.est.1c00159