Inhaled agents and the environment

Inhaled agents and the environment

This Sunday session at Euroanaesthesia in Vienna addressed the growing concerns about the impact of inhaled anaesthetic gases on the environment.

Global warming is one of the greatest threats to the survival of the human race. Multiple and complex factors influence this process. The gases and vapours used during anaesthesia may contribute to the greenhouse effect and destruction of the ozone layer, but it should also be remembered that production and delivery of all drugs contributes to processes that leave a carbon footprint.

The speaker for this session was environmental chemist Professor Ole John Nielsen of the University of Copenhagen, who was part of the IPCC (Intergovernmental Panel on Climate Change) that was awarded with the Nobel Peace Prize in 2007.

He discussed isoflurane (CF3CHClOCHF2), desflurane (CF3CHFOCHF2) and sevoflurane ((CF3)2CHOCH2F), that are among halogenated organic compounds used for induction and maintenance of general anaesthesia. Isoflurane entered broad clinical use in the early 1980s, followed by desflurane and sevoflurane a decade later.

“These volatile anaesthetic gases are delivered via a system that mixes the anaesthetic gas with a carrier gas (oxygen and nitrous oxide) in various concentrations,” explained Prof Nielsen. “Exhaled gases flow through an absorber, most commonly, calcium hydroxide, which are used to remove carbon dioxide. Some gas may at the same time escape from the delivery system.”

Although the increasing abundance of CO2in the atmosphere is the main driver observed climate change today, it is the cumulative effect of all forcing agents that dictates the direction and magnitude of the change, and many smaller contributors are also at play. Isoflurane, desflurane, and sevoflurane, are widely used inhalation anaesthetics.

“We have measured the infrared spectra of these anaesthetics and conducted the first calculations of their contribution to radiative forcing of climate change which recognise the important fact that radiative forcing is strongly dependent on the wavelength of the absorption features,” said Dr Nielsen.

“We calculated, based on ‘global warming potential’ of each of these gases, the average climate impact per anaesthetic procedure at the University of Michigan is the same as the emission of approximately 22 kg CO2. We further estimated the annual global emissions of inhalation anaesthetics have a climate impact which is comparable to that from the CO2 emissions from 2 coal fired power plants or 1 million passenger cars.”