About & Methodology
Evidence base, assumptions, and calculation methodology used across the application.
Anaestreesia is a clinical tool designed to estimate the carbon footprint of anaesthetic practice. It is intended for education, audit, and reflective practice rather than precise emissions measurement.
The tree figure represents an estimate of how many mature trees would be required to absorb the calculated carbon dioxide emissions from a single anaesthetic over the course of one year.
It is derived by dividing the total CO₂-equivalent emissions by a standard annual sequestration rate per tree. This is used purely as a visual comparator to help contextualise emissions in a clinically meaningful way.
This value should be interpreted as an approximation rather than a precise ecological offset calculation, as real-world carbon sequestration varies significantly by tree species, age, climate, and geography.
The volatile anaesthesia calculator estimates greenhouse gas emissions by calculating the quantity of volatile anaesthetic delivered from routinely recorded clinical variables. The initial equation was published by Cuveele et al (2023). This equation has been chosen to ensure ease of use, though may decrease accuracy of the estimated consumption of volatile agents by around 5%.
Vapour Consumption
Vapour consumption is calculated using the equation:
Where:
- FVAP = equivocal vaporisor setting (%)
- FIN = inspired volatile concentration (%)
- DS = physiological dead-space fraction (agent specific)
- FET = end-expired volatile concentration (%)
- FGF = fresh gas flow (L/min)
- MV = minute ventilation (L/min)
Physiological dead-space fractions:
- Sevoflurane: 0.49
- Desflurane: 0.66
- Isoflurane: 0.59
Conversion to Liquid Anaesthetic
The FVAP is first converted from a percentage into a fraction, which is then used, along with FGF and duration of anaesthetic, to calculate the volume of vapour produced.
Vapour volume is converted to liquid anaesthetic using published vapour-to-liquid expansion factors:
- Sevoflurane: 184 mL vapour per mL liquid
- Desflurane: 210 mL vapour per mL liquid
- Isoflurane: 195 mL vapour per mL liquid
Carbon Dioxide Equivalent (CO₂e)
The liquid volume is converted into greenhouse gas emissions using the physical density of each volatile agent together with its published 100-year Global Warming Potential (GWP100).
| Agent | Density (g/mL) | GWP100 |
|---|---|---|
| Sevoflurane | 1.52 | 127 |
| Desflurane | 1.47 | 2540 |
| Isoflurane | 1.50 | 510 |
These calculations estimate the direct greenhouse gas emissions resulting from release of volatile anaesthetic to the atmosphere, consistent with current life-cycle assessment methodology and the contemporary anaesthetic sustainability literature.
Anaestreesia currently reports results using conventional GWP values to maintain consistency with the published anaesthetic sustainability literature and existing life-cycle assessments. As the evidence base evolves, future versions of the application may incorporate alternative climate metrics, including GWP*, to enable comparison between different approaches to estimating environmental impact. See the "Carbon Factors" section for more details.
Where selected by the user, the carbon footprint of additional anaesthetic consumables (e.g. syringes and drawing-up needles) is calculated separately and added to provide an estimated total carbon footprint for the anaesthetic.
The TIVA calculator estimates the carbon footprint of intravenous anaesthesia using published life-cycle assessment (LCA) data for pharmaceuticals and single-use consumables.
Carbon factors are based on the work of Elson et al., which synthesised pharmaceutical manufacturing data from Hu et al. together with life-cycle inventories for anaesthetic consumables. The calculator estimates emissions from the manufacture and disposal of drugs and consumables rather than direct atmospheric release.
Total Carbon Dioxide Equivalent (CO₂e)
The calculator also reports the volume of propofol opened, administered and wasted for audit and quality improvement purposes. Carbon emissions are currently based on opened drug vials rather than unused drug volume.
| Item | CO₂e (kg) |
|---|---|
| Propofol 50 mL vial | 0.1546 |
| Propofol 100 mL vial* | 0.3092 |
| Remifentanil vial | 0.0217 |
| 20 mL syringe | 0.0519 |
| 50 mL syringe | 0.1282 |
| Drawing-up needle | 0.0061 |
| TIVA administration set | 0.3718 |
| Processed EEG sensor | 0.8333 |
*The 100 mL propofol value is currently estimated by scaling the published 50 mL value according to drug content. This will be updated should vial-specific life-cycle assessment data become available.
Carbon footprinting in healthcare is an evolving field. The values used within Anaestreesia are based on the best available published life-cycle assessment (LCA) data and internationally recognised greenhouse gas metrics. They should be interpreted as estimates rather than precise measurements.
Reported carbon dioxide equivalent (CO₂e) values vary between studies because of differences in methodology, system boundaries, geographical location, manufacturing processes, electricity generation, transport, waste disposal and assumptions made during life-cycle assessment. Where multiple published values exist, Anaestreesia uses contemporary, peer-reviewed data that are transparent and reproducible.
For volatile anaesthetic agents, greenhouse impact is calculated using the Intergovernmental Panel on Climate Change (IPCC) 100-year Global Warming Potential (GWP100), which remains the standard metric used in anaesthetic sustainability research. Alternative measures, such as GWP20, place greater emphasis on short-term climate effects and may produce substantially different values, particularly for desflurane. These metrics answer different scientific questions and neither should be considered universally "correct".
GWP100 and GWP20 convert the mass of emitted anaesthetic into an equivalent mass of carbon dioxide over fixed 100- and 20-year time horizons, respectively, and remain the internationally recognised standards for life-cycle assessment and greenhouse gas reporting. However, volatile anaesthetic agents are short-lived climate pollutants, and these metrics may overestimate their long-term warming effect because they do not distinguish between the transient behaviour of short-lived gases and the cumulative nature of carbon dioxide. GWP* has recently been proposed as an alternative framework that more closely reflects the temperature response to short-lived climate pollutants by incorporating changes in emission rates over time, rather than cumulative emissions alone.
Similarly, the carbon footprint of intravenous anaesthesia depends on life-cycle assessment of pharmaceutical manufacture and disposable consumables. These estimates continue to evolve as more manufacturers publish primary environmental data and life-cycle methodologies improve.
The purpose of Anaestreesia is not to provide an exact measurement of greenhouse gas emissions for an individual anaesthetic, but to offer a transparent, evidence-based estimate using a consistent methodology. This allows meaningful comparison between techniques, supports education, facilitates quality improvement projects and encourages informed discussion about sustainable anaesthetic practice.
- 1. Ryan SM, Nielsen CJ. Global warming potential of inhaled anaesthetics: application to clinical use. British Journal of Anaesthesia. 2010;105(6):760–766.
- 2. Hu X, Pierce JMT, Taylor T, Morrissey K. The carbon footprint of general anaesthetics: a case study in the UK. Resources, Conservation and Recycling. 2021;167:105411.
- 3. Cuveele L, Hendrickx JF, De Wolf AM, De Cooman S, Chesebro BB, Feldman J, Sherman J. Development and validation of a model to calculate anesthetic agent consumption from inspired and end-expired concentrations, minute ventilation, fresh gas flow and dead space ventilation. Journal of clinical monitoring and computing 2023; Feb;37(1):227-35.
- 4. Elson B, Steinbach I, Hillson R. Carbon footprint of total intravenous anaesthesia vs. inhalational sevoflurane anaesthesia in adults: a modelling study. Anaesthesia. 2026;81(3):332–342.
- 5. Hodnebrog Ø, et al. Updated Global Warming Potentials and Radiative Efficiencies of Halocarbons and Other Weak Atmospheric Absorbers. Reviews of Geophysics. 2020.
- 6. Intergovernmental Panel on Climate Change (IPCC). Climate Change 2013: The Physical Science Basis (Fifth Assessment Report). Cambridge University Press.
- 7. Royal College of Anaesthetists. Environmental Sustainability Guidance and Annual Anaesthetic Department Calculator.
- 8. United States Environmental Protection Agency (EPA). Greenhouse Gas Equivalencies Calculator.
- 9. United States Department of Agriculture (USDA) Forest Service.
- 10. Slingo JM, Slingo ME. Desflurane and carbon‐based economics. Anaesthesia. 2026;82
- Anaestreesia estimates greenhouse gas emissions (CO₂-equivalent) using published physical properties of volatile anaesthetic agents, peer-reviewed Global Warming Potential values, and life-cycle assessment data for consumables. Calculations are intended to support education, quality improvement and sustainability initiatives, and should be interpreted as estimates rather than direct measurements.
Anaestreesia v.1.0.1 - Educational carbon estimation tool