Delivering environmental sustainability through informed volatile awareness – the destiva.app

The carbon footprint of volatile anaesthesia is well recognised [1]; the environmental impact of a surgical case is significantly determined by the choices and practices of the anaesthetist and therefore, unlike other clinical specialties, anaesthesia is uniquely empowered to lead the change towards sustainable healthcare. Like any quality improvement project, data is key to driving green anaesthesia. Modern anaesthetic machines record extensive logbooks from thousands of cases featuring detailed records of fresh gas flows, gas and volatile consumption that can be exported to USB flash drives. These exported logs form the basis for the webtool to generate individualised, benchmarked, and near real-time information for anaesthetic departments to use for feedback and quality improvement.

Developing the webtool

Initially, from our interest in data science, we started exploring the logbook exports from our anaesthetic machines and generating reports on our department’s environmental impact. Recognising the value of this resource, we developed a free online webtool that allows anybody to upload the exported logbooks for Dräger Perseus and Atlan machines and analyse their carbon footprint from the use of volatile anaesthetics and nitrous oxide.

Several logbooks can be uploaded simultaneously and processed to produce charts and tables to show clearly a department’s use of their anaesthetic machines and associated environmental impact. These charts and tables can then be downloaded as a ready-made PowerPoint file for audit meetings or single-sheet summary documents for ongoing feedback. Whilst clinicians know in general terms that desflurane, nitrous oxide, and high fresh gas flow rates are bad for the environment, the webtool aims to demonstrate specific values for individuals and departments.

Key features of the webtool

These include: 

• Total usage of sevoflurane, isoflurane, desflurane and nitrous oxide 
• Clinicians’ choices of fresh gas flow rates across cases 
• Global warming potential expressed in CO₂ equivalents and benchmark terms (equivalent tonnes of coal, air miles, and miles driven in a petrol car) 
• Ability to deep dive into specific cases and see fresh gas flow use over the course of the case and overall environmental impact of that case 
• A demonstration mode that allows exploration of a built-in dataset to discover the features of the platform and see the impact of a typical anaesthetic department 
• Information for users on how to obtain data from their machines

To ensure trust in the webtool, we have emphasised transparency when calculating environmental impact and have made use of widely accepted values for global warming potentials of various agents [2], as well as data from the National Carbon Trust for generating real-world examples (Table 1). Early users of the webtool requested that TIVA be included in the reports; this requires some assumptions as it is not included in the logbook. The webtool assumes that any case that last longer than 5 minutes, with detectable end tidal CO₂, no detectable volatile, and positive pressure ventilation represents TIVA rather than sedation or routine machine testing. For the environmental impact of TIVA, we used an example estimation derived from Allen and Baxter’s work [3]. This represents a common ‘two pump’ remifentanil and propofol approach. We aim to update our TIVA estimates as more detailed modelling is published. destiva.app in our department.

From the webtool’s report of our department’s practices, several key points were apparent. Firstly, the greater proportion of climate impact from the department was coming from a small number of cases that utilised high impact techniques such as desflurane (Figure 1) or nitrous oxide (Figure 2); 50% of our atmospheric emissions originated from less than 10% of cases. Variations in weekly emissions suggested that this related to individuals’ anaesthetic practice. Secondly, although in our department we had previously focussed on minimising desflurane use, our nitrous oxide consumption had a similar carbon footprint although over a greater number of cases. Thirdly, while departmental colleagues expressed their intention to use low-flow anaesthesia, what that meant in practice was quite variable. The mean fresh gas flow during the maintenance phase was 1.5 l.min^-1 for sevoflurane and 0.7 l.min^-1 for desflurane. Additionally, we would frequently see cases where the fresh gas flow rate was not lowered after induction, or was increased significantly during the case as a result of, presumably, clinical emergencies or human error. This discrepancy between intention and implementation needs to be factored in when considering the effectiveness of low-flow anaesthesia as a sustainable option.

From the webtool we could see that for our department: 

• Approximately 10% of cases utilise nitrous oxide; TIVA utilisation ranges from 10-20%. 
• In November 2021 our nitrous oxide and volatile emissions for 676 cases had a global warming potential equivalent to 7575 kg CO ₂eq (or burning 3.2 tonnes of coal). 
• In a single case lasting 6 h 58 m using desflurane, the global warming potential equalled 1001 kg CO ₂eq (equivalent to 3.9 return flights from Heathrow to Paris). 
• A single 13-hour case using TIVA had a carbon footprint similar to driving 21 miles in a petrol car.

The reaction from colleagues to the data was very insightful. People are often surprised that, even when the burden of the plastics is taken into account, TIVA is still significantly less environmentally impactful than volatile anaesthesia. This represents the power of utilising concrete data, especially so when global warming potential of volatile anaesthesia is expressed in equivalent tonnes of coal. Furthermore colleagues frequently equate the carbon footprint savings of a low-flow volatile technique to that of switching to TIVA, but this is not the case. Based on our real-world findings, TIVA appears to have a carbon footprint significantly less than volatile anaesthesia. In addition, we have not been able to capture data from induction, unless performed in theatre, as the Dräger Primus machines in our anaesthetic rooms do not offer downloadable logbooks; therefore, a significant proportion of volatile consumption associated with higher gas flows is not being recorded, and the impact of volatiles remains understated in the data. In summary, destiva.app is a grassroots-produced webtool to streamline and simplify the collection and presentation of data to promote behaviour change towards increase sustainability in anaesthesia. We invite all anaesthetists to make use of the tool to grasp more fully their department’s environmental impact.

Table 1. Examples of carbon footprints across typical cases 

(Below) Figure 1. Departmental anaesthetic agent CO₂ equivalent production by week

(Below) Figure 2. Relative contributions of anaesthetic modalities to carbon footprint by case numbers and total anaesthetic duration

Acknowledgments: Dr Tom Colville who named the webtool from his sustainability work with Mersey Mates

Nick Lown
Consultant Anaesthetist
Liverpool University Hospitals NHS Foundation Trust, Lower Lane, Liverpool 

Charlotte Berwick
ST7 Anaesthesia
Mersey Deanery 

Twitter: @gas_liverpool

References 

1. NHS England. Delivering a “net zero” National Health Service, 2021. https://www.england.nhs.uk/greenernhs/wp-content/uploads/sites/51/2020/10/delivering-a-net-zero-national-health-service.pdf (accessed 4/4/2022). 
2. Pierce J. The environment, the gas bill, and the route to sustainable anaesthesia. RCoA Bulletin 2013; 82: 39-41. 
3. Allen C, Baxter I. Comparing the environmental impact of inhalational anaesthesia and propofol-based intravenous anaesthesia. Anaesthesia 2021; 76: 862-3.

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