Although volatile anaesthetic agents (such as isoflurane and sevoflurane) are emitted in relatively low quantities into the environment, they are disproportionately effective greenhouse gases, owing to their ability to absorb infrared radiation within an atmospheric ‘cooling window’ in which absorption of radiation is normally minimal. In fact, one hour of equine anaesthesia (using sevoflurane) may be equivalent to driving up to 184 miles.
Fortunately, a few simple changes to our equine anaesthetic protocols can significantly reduce release of these agents into the environment:
• Reduce anaesthetic time. Where appropriate, consider clipping surgical sites prior to anaesthesia; ensure the theatre team are present and coordinated, and minimise avoidable delays during anaesthesia.
• Regular servicing and checks. The gas manifolds, intermediate pressure system, vaporiser, anaesthetic machine, breathing systems and endotracheal tubes are all sources of leaks and wastage.
• Pre-filling the breathing system. Pre-filling the reservoir bag/ventilator bellows with oxygen/volatile agent enables earlier reduction of fresh gas flow (FGF) and vaporiser settings. A bung can be used to close the patient end of the breathing system between cases.
• Reduce FGF. Where volatile agents are vented to the atmosphere (as with most active scavenging systems) and not captured, reducing FGF results in proportional reductions in greenhouse gas impacts. Whilst this should be performed within the clinician’s capabilities and the manufacturer’s equipment guidelines (see link to article, below), this is one of the most effective measures for reducing emissions of volatile anaesthetic agents.
• Recapture and reuse of volatile anaesthetic agents. This promising technology is being trialled in NHS trusts, and life cycle analysis suggests this has potential to significantly reduce carbon emissions from inhalational anaesthesia.
• Consider total intravenous anaesthesia (TIVA). The carbon footprint has been calculated for various active ingredients and TIVA is likely to have a lower carbon footprint over its life cycle than inhalational agents. However, this technique is currently only suitable for short procedures, and consideration must be given to additional environmental impacts such as single-use plastics, waste disposal, energy use, and ecotoxicity of excreted drugs/metabolites.
• Ensure sufficient sedation/analgesia. Where safe and appropriate, some procedures may be carried out in conscious or sedated horses. Additionally, the use of analgesia, MAC-sparing techniques (such as partial intravenous or regional anaesthesia), or drugs which stabilise the depth of anaesthesia (preventing the need for rapid increases in depth of anaesthesia) all reduce reliance on volatile anaesthetic agents and thus limit inhalant emissions.
For more hints and tips, as well as further information, take a look at the recent EVE editorial ‘Sustainable development in equine anaesthesia’.