Original research
Figure 2 System boundaries for Penthrox. The system boundary shows the ‘cradle-to-grave’ analysis of the life cycle impact assessment. This is a simplified representation of all ‘flows’ shown in online supplemental appendix 3. *The manufacture of methoxyflurane from its raw materials has been considered as a separate process from other raw materials in the results to allow for contribution analysis.
charcoal. Perfect technique, as guided by the manufacturer, was assumed in our analysis. Around 35% of the inhaled methoxy- flurane is exhaled unchanged with the rest absorbed by the body. The exhaled methoxyflurane is captured by the charcoal, reducing the exhaled concentration of methoxyflurane to the environment to zero, as described by the manufacturer. 16 This project assumed complete patient compliance with the instruc- tions of exhalation into the device and 100% effectiveness of the charcoal. The literature is less clear about the exact outcome of the 65% of 3 mL methoxyflurane that is absorbed by the human body. Studies have shown the metabolised products to be organic fluorine, fluoride and oxalic acid (29%, 7.7% and 7.1%, respec- tively). 20 For the purposes of this study, the remaining 21.2% of methoxyflurane is assumed to be excreted unchanged. Disposal Although many component parts of Penthrox are easily recy- clable, experience shows that the practicalities of recycling in clinical environments makes this unlikely to happen. For the purposes of this project, and the likely real-life disposal after use, all components were assumed as being discarded into hazardous waste bins and incinerated. Data analysis Data from Ecoinvent were modelled and analysed in OpenLCA. Table 1 includes both the impact category results and the LCIA methods used within this study alongside a description of each category. Contribution analysis of different parts of the LCIA was also assessed using five distinct areas: raw materials, methoxyflu- rane manufacture, production processes, transport and disposal. OpenLCA also calculated the normalised impact and disability- adjusted life years (DALYs). Comparative analysis of Penthrox No complete LCIA was currently available online for N 2 O. Climate change impact was available online for Entonox. 21 Data from the study by Pearson et al were extrapolated to represent 30 min continuous use of Entonox at a minute volume rate of 14 L/min.
reactions are required to manufacture methoxyflurane (online supplemental appendix 2) and were considered in the LCIA. 13–15 Bond energies were used to determine the energy change within each reaction. If energy was required, it was input into the LCIA as electricity demand and if energy was released it was listed in the LCIA as steam output. The by-products from reaction 2 were unclear from source material, therefore, assumed products were 1,1-dichloro-2,2-difluoroethylene, dichloromethane and water. Methoxyflurane is distributed/manufactured by Medical Developments International Limited (MDI) based in Victoria, Australia. It was assumed that the drug was manufactured on site at Scoresby Manufacturing facility in Melbourne, Australia, as this information was not available. An MDI representative provided information on the energy source at the Scoresby Manufacturing facility, explaining that the company has installed a solar array providing 750 MW of electricity, which was consid- ered in the LCIA. 16 Product manufacture Component part and weight information was gathered from the manufacturer in June 2022. 16 Manufacturing processes involved within the production of Penthrox were assumed and energy requirements of the machines involved within these processes were correlated with online literature. 17 Transportation MDI provided information on transport logistics of Penthrox. 16 The end location used in this project was University Hospital Southampton, UK. Road distances were calculated using Google Maps and shipping distances were calculated using www.ports. com. 18 19 Modes of transport include by truck and ship and appropriate fuel types were assumed. Summary of transport data is shown in online supplemental appendix 3. Use Penthrox requires no additional components for its use. The 3 mL vial of methoxyflurane is emptied into the chamber containing the wick. The user then forms an oral seal around the mouthpiece and inhales. They then exhale back into the device, where the valve causes the exhaled gases to pass through
Martindale AEV, et al . Emerg Med J 2024; 41 :69–75. doi:10.1136/emermed-2022-213042
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