key: cord-0965329-nu6c6vfk
authors: McGain, Forbes; Muret, Jane; Lawson, Cathy; Sherman, Jodi D.
title: Environmental sustainability within anaesthesia and critical care
date: 2020-08-12
journal: Br J Anaesth
DOI: 10.1016/j.bja.2020.06.055
sha: e788e4246cce14f28dd7b548c894406572b53abd
doc_id: 965329
cord_uid: nu6c6vfk

The detrimental health effects of climate change continue to increase. Although health systems respond to this disease burden, healthcare itself pollutes the atmosphere, land, and waterways. We surveyed the ‘state of the art’ environmental sustainability research within anaesthesia and critical care, addressing why it matters, what is known, and ideas for future work. Focus is placed upon the atmospheric chemistry of the anaesthetic gases, recent work clarifying their relative global warming potentials, and progress in waste anaesthetic gas treatment. Life cycle assessment (LCA; i.e. ‘cradle to grave’ analysis) is introduced as the definitive method used to compare and contrast ecological footprints of products, processes, and systems. The number of LCAs within medicine has gone from rare to an established body of knowledge in the past decade that can inform doctors of the relative ecological merits of different techniques. LCAs with practical outcomes are explored, such as the carbon footprint of reusable vs single-use anaesthetic devices (e.g. drug trays, laryngoscope blades, and handles), and the carbon footprint of treating an ICU patient with septic shock. Avoid, reduce, reuse, recycle, and reprocess are then explored. Moving beyond routine clinical care, the vital influences that the source of energy (renewables vs fossil fuels) and energy efficiency have in healthcare's ecological footprint are highlighted. Discussion of the integral roles of research translation, education, and advocacy in driving the perioperative and critical care environmental sustainability agenda completes this review.

The scientific foundation for environmental sustainability within anaesthesia and critical care has progressed rapidly during the past decade, particularly with the incorporation of environmental life cycle assessments (LCAs). As a result of these new studies, anaesthetists and critical care physicians can make informed choices to reduce their environmental footprint.

Translational research on recent environmental footprinting studies into routine anaesthetic/ICU practice is particularly required.

The climate crisis is the largest and most prolonged threat to global health ever described. 1 Owing to anthropogenic greenhouse gas (GHG) emissions, the temperature of the planet has been rapidly increasing since the Industrial Revolution. 2, 3 The health implications associated with climate change are increasingly widespread. 1, 4 The Intergovernmental Panel on Climate Change (IPCC) Special Report concluded we have less than 10 yr to dramatically reduce our GHG emissions to limit global warming to an increase of 1.5 C and limit climate change-related public health disasters. 2 This call for flattening of the GHG curve is analogous to global efforts to slow the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission to allow for a more manageable response. 5 The Hippocratic oath to First do no harm guides physician practice, yet healthcare itself pollutes and harms public health. 6 If global healthcare were a country, it would be the fifth largest carbon emitter on the planet. 7 Sustainability is a guiding principle that 'meets the needs of the present generation without compromising the ability of future generations to meet their own needs, 8 and may reconcile this discrepancy. Sustainable healthcare requires balancing patient outcomes with economic, environmental, and social costs. 9 Practising more sustainability and protecting the environment is important to the overwhelming majority of UK healthcare staff. 10 Much of the environmental emissions generated by healthcare are indirect, or embodied in upstream manufacturing of products and energy that support healthcare facilities. 7, 11 In the infancy of the sustainability movement, efforts tended to focus on highly visible endeavours such as solid waste recycling efforts, and carbon emissions reductions. A broader view encompasses emissions to air, water, and soil, enables holistic environmentally preferable choices, and addresses efficient use of natural resources towards a circular economy. 1 Anaesthetists and critical care physicians are in positions of authority and responsibility to make valuable contributions in the transition to sustainable healthcare.

Although climate change was initially postulated by Fourier in the 1820s, 12 it was not until the 1970s that real concerns emerged of the dire consequences of increasing GHG emissions, with the majority of increases occurring after 1980. 13 Since the 1960s the effects of other increasing GHGs (mainly CH 4 , N 2 O, O 3 , and halogenated compounds) have contributed as much to global warming as increasing CO 2 itself, 14 with halogenated compounds (including volatile anaesthetic agents) accounting for approximately 11%. 15 Nitrous oxide is responsible for the majority of ongoing ozone depletion, 16 and approximately 6% of anthropogenic global warming. 15 The term CO 2 equivalent (CO 2 e) is used to indicate the global warming potency of GHGs relative to the reference unit of CO 2 .

All heteronuclear gases (possessing more than one type of atom, e.g. CO 2 , H 2 O), and limited homonuclear molecules (e.g. ozone [O 3 ]) are infrared active, meaning they vibrate/rotate/ stretch in the presence of infrared radiation. 17, 18 Molecular absorption, and later emission, of infrared light leads to heat retention (reduction of heat radiation from earth to space), described by the term global warming potential (GWP). Carbon dioxide has, by definition, a GWP of 1, whereas N 2 O for example has a GWP of 265. 13 The IPCC (the leading international scientific authority on climate change) uses the 100 yr time horizon GWP (GWP 100 ) as the standard comparison of long-lived GHG effects, 13 although shorter GWPs (e.g. 20 yr) can be suitable for the relatively ephemeral volatile anaesthetics. 19, 20 A gas's GWP depends upon two factors. Firstly, radiative efficiency, that is the change in solar energy irradiance (W m À2 ) on the earth's atmosphere that occurs with a change in the concentration of a particular compound, is routinely given as parts per billion (i.e. W m À2 ppb À1 ). 13 Radiative efficiency depends on the strength and position of the compound's infrared absorption bands. Secondly, GWP depends upon the gas' atmospheric lifetime, measured as the time constant, t¼time to 37% (1/e) initial concentration. 13 The halogenated anaesthetic ethers isoflurane, enflurane, and desflurane have similar radiative forcings, with sevoflurane about 25% less, 21, 22 whereas the alkane halothane (lacking the intense infrared absorption of an ether group) has about half of sevoflurane's radiative forcing. 22 The atmospheric lifetime of a molecule depends upon how rapidly it is broken down, particularly by the OH e radical (the atmospheric 'detergent'). 23 The bond strength of carbonefluorine (CeF) is greater than that of CeH, CeCl, and CeBr, 24 and so atmospheric OH e radicals less easily displace F atoms. Thus, sevoflurane, isoflurane, and desflurane respectively have differing atmospheric lifetimes of 1, 3, and 14 yr. 25 Fluorinated desflurane has a longer lifetime than the closely related isoflurane (Cl e substituted for F e ), 24 whereas the CF 2 H moiety of desflurane and isoflurane is less reactive to OH e radicals than sevoflurane's CH 2 F. 21, 26 OH e radicals also react more readily with halocarbon molecules where the C atoms have themselves more C atoms attached to them; for example a tertiary C atom (bound to three other C atoms) is more reactive than secondary or primary C atoms. 26 Sevoflurane, (CF 3 ) 2 C*HOCH 2 F, has a C atom (C*), attached directly to two C atoms and a third C atom via the ether group, making it more reactive to OH e than desflurane or isoflurane. 26 These small differences between sevoflurane and desflurane explain why sevoflurane's lifetime is less than 10% than that of desflurane. 21 The GWPs of halothane, isoflurane, enflurane, and sevoflurane were quantified by Brown and colleagues. 22 Langbein and colleagues 26 studied these gases and desflurane, with further work by Ryan and Nielsen. 20 Sulbaek Andersen and colleagues 21 provide the most recent and comprehensive examination of anaesthetic gases' GWPs (which we use here). Importantly, volatile anaesthetic GWP variability is primarily caused by differences in atmospheric longevity rather than radiative forcing. The GWP 100 of desflurane is 2540 21 (1 g desflurane has the same GWP as 2540 g CO 2 ), sevoflurane 130, 21, 25 isoflurane 510, 25 and N 2 O approximately 265. 13 The potent analgesic methoxyflurane (CH 3 OCF 2 CHCl 2 ) has multiple CeH bonds and a resultant atmospheric lifetime of 54 days, with a GWP of only 4. 27 The GWP of nitrous oxide has been revised down from 300 to 265 in the 2013 IPCC report, because of improved quantification, particularly the effects of increasing CO 2 levels upon the CO 2 eN 2 O infrared absorption spectra. 13 Per mass, desflurane has a GWP approximately 20 times that of sevoflurane, five times that of isoflurane, and 10 times that of N 2 O. Notably, desflurane also has about one-third of the potency of sevoflurane.

Measured atmospheric concentrations of volatile anaesthetics were first published in 2016 by Vollmer and colleagues, 28 demonstrating that desflurane pollution was increasing, sevoflurane's static, with halothane and isoflurane's decreasing. Desflurane contributed 80% of the estimated greenhouse effect from all measured volatile anaesthetic pollution (3Â10 6 tonnes CO 2 e emissions per annum [p.a.]). 28 Nitrous oxide was excluded, because anaesthetic/non-anaesthetic sources of atmospheric N 2 O were indistinguishable. 28 These data were in approximate agreement with those of Sulbaek Andersen and colleagues, 19 who estimated 4.4Â10 6 tonnes CO 2 e emissions p.a. from volatile anaesthetics (not N 2 O) via a 'bottom up' extrapolation from one US institution that did not use desflurane. A similar estimation of 5Â10 6 tonnes of CO 2 e emissions p.a. from global volatile anaesthetic gas use was made by White and Shelton 29 from online market sources (excluding N 2 O). 30 As a proportion of total anthropogenic CO 2 e emissions, volatile anaesthetics used in human healthcare may be responsible for 0.1% of global warming, equivalent to 1 million US cars on the road. 25, 31 Worldwide anaesthetic N 2 O use is estimated to contribute between 1% 32 and 3% 33 of N 2 O's global emissions. 15 The UK's NHS estimated that 5% of the total carbon footprint of an acute NHS organisation was attributable to anaesthetic gases, particularly N 2 O. 34 A considerable, although unknown, amount of N 2 O is used in healthcare activities outside the operating suite in undefined air ventilation conditions. 35 The earth's ozone layer protects life from harmful UV rays. The 1987 Montreal Protocol 36 aimed to phase out anthropogenic ozone depleting substances such as chlorofluorocarbons (CFCs), and has been highly successful, in stark contrast to the 2016 Paris Agreement on climate change. 37 Atmospheric Cl, and particularly Br atoms, form ozone depleting radicals, so halothane has an ozone-depleting potential (ODP), although its use is declining globally. Fluorine does not destroy O 3 ; thus, sevoflurane and desflurane have no ODP. 38 Nitrous oxide is also ozone depleting. 16 Because the Montreal Protocol successfully limited release of CFCs, anthropogenic N 2 O generation is at present responsible for most ongoing ozone depletion. 16 The global contribution of anaesthetic N 2 O use should not be ignored. 39 Limiting N 2 O emissions would be beneficial for both ozone protection and climate change mitigation.

The CO 2 e emissions from a single anaesthetist's daily routine use of inhalation agents can be large. 40e42 When expressing these CO 2 e emissions as equivalent distance driven, it is unfortunately easy to 'drive more than 1000 km per day', even using low flow (1 L min À1 ) desflurane and N 2 O. 41, 43 Such 'miles driven' has even prompted calls to 'abandon inhalation anaesthesia' in editorials. 29 One MAC-hour (2.2% sevoflurane, 1.2% isoflurane, 6.6% desflurane, at 1 L min À1 fresh gas flow [FGF]) with sevoflurane is equivalent to driving 4 mi (6.5 km), 40 isoflurane 8 mi (13 km), 40 and desflurane 190 mi (300 km). 40, 43 Alternatively, combining 0.6 MAC N 2 O for the hour results in an additional 60 mi (100 km) 44 beyond the 0.4 MAC 2 mi (3 km) of sevoflurane. 40 The GHG effect of N 2 O and desflurane are similar per MAC-hour (60% FiN 2 O¼0.6 MAC). 43 The most important, safe, and effective measures that anaesthetists can take individually to reduce their carbon are to: (1) avoid desflurane and N 2 O, (2) practice low-flow anaesthesia, and (3) embrace techniques to minimise the requirement for inhalation agents, such as regional and total intravenous anaesthesia (TIVA). These techniques are encouraged by the ASA Task Force on the Environment, when clinically appropriate. 45 Free teaching tools for estimating one's personal anaesthetic 'carbon footprint' include Yale Gassing Greener 46 and the Association of Anaesthetists Anaesthetic Gases Calculator. 47 Waste anaesthetic gas scavenging, destruction, and recycling Waste anaesthetic gases (WAGs) are vented to the outdoor atmosphere, virtually unmetabolised, and unregulated. Minimum flow anaesthesia (<1 L min À1 FGF) is a safe, efficient, simple, and reliable means to reduce WAGs. 48e50 Concern about theoretical compound A-induced nephrotoxicity in humans from low flow sevoflurane has driven vast amounts of waste globally, 42,51 despite safety evidence 20 yr ago, 52 and newer non-compound A producing CO 2 absorbers. 51 Lower FGFs reduce CO 2 absorbents' lifetimes, although the overall financial cost of the anaesthetic is still reduced 53, 54 and can be further minimised by changing absorbers only when indicated by the capnographic appearance of inspired CO 2 .

Venting to the atmosphere can be mitigated via WAG capture and destruction technologies, some of which are commercially available already. 55e59 Recaptured volatile drugs may be adsorbed, and then either subsequently destroyed or desorbed, separated, and stored for potential reuse. N 2 O is relatively inexpensive and difficult to capture; however, its destruction could dramatically reduce its harmful GWP and ODP effects, and is already routinely performed in Sweden. 60 Activated charcoal contains a porous, favourable adsorption surface, and is used by veterinarians and dentists to capture volatile anaesthetics (not N 2 O) in lieu of expensive scavenging systems, to reduce occupational exposure. 55 Activated charcoal can also be used to enable limited rebreathing of volatile anaesthetic gases. 56 Adsorbed volatiles (as the patient breathes out) are desorbed readily (as the patient breathes in), enabling the rebreathing of the volatile; however, efficiency is lost at higher flows. This system is primarily used in critical care where liquid volatile agents are delivered directly into the respiratory circuit; however, use is limited because of occupational exposure concerns. Volatile anaesthetics quickly desorb and emit to the atmosphere upon charcoal device disposal, and so this technology has shortterm benefit only. 40 Metal organic frameworks (MOFs) are solid crystalline compounds in which metal ions (e.g. Zn 2þ ) are linked by bridging organic molecules to create open networks that are able to accommodate guest molecules within pores. 57 MOFs are alternatives to charcoal for capturing volatile anaesthetics, with the advantage of precise control of pore size. Commercially available aluminosilicates (zeolite) can also adsorb volatile anaesthetics, including xenon. 58, 59, 61 Volatile aluminosilicates can be desorbed and condensed, and then either re-purified or destroyed. 58 Another adsorption/ condensation system in development uses supercritical CO 2 before passing reclaimed drug through a purification process for potential reuse. 62 Some WAG capture units have separate components that condense volatile anaesthetics 63 and destroy N 2 O with a heated catalyst. Nitrous oxide from maternity wards of Sweden is routinely destroyed using rooftop installations. 60 It is possible to destroy both volatile gases and N 2 O with a simple scavenging circuit UV lamp, although the efficiency of removing UV-resistant N 2 O is much less (<10% N 2 O destroyed). 64 Membrane technologies that filter through CO 2 , O 2 and N 2 into the scavenging interface, whilst preventing the larger volatile anaesthetics from escaping into the scavenging stream, are also being actively examined. 65 Anaesthesia scavenging interfaces continuously entrain large air volumes, diluting the WAGs and reducing suitability for effective volatile 'cold trap' condensation. 66 A commercially available dynamic scavenging interface has an ondemand, one-way valve that dramatically reduces air entrainment, and therefore WAG dilution, and may significantly reduce scavenging system energy requirements and costs. 67 Notably, only scavenged WAG is treated. Furthermore, higher FGFs reduce WAG capture and treatment efficiency because of dilution. 66 Industry claims of WAG capture efficiency therefore require validation. Importantly, reclaimed drug is not yet approved for re-use, resulting in either a storage problem until such approval, or potential worsening of emissions depending on waste management procedure. Nevertheless, such technologies are promising, and could considerably reduce GHG emissions.

Life cycle assessment (LCA) is a scientific method for analysing the 'cradle to grave' environmental 'footprint' associated with natural resource extraction, manufacturing, packaging, transport, use/reuse, and recycling/waste disposal of products or processes. 68, 69 There are four phases integral to proper LCA methodology as described by the International Organization for Standardization (ISO), ISO-14000 series of standards. 70 First, is describing the goal and scope of the LCA. A functional unit refers to the object/process of interest. For example if one opens an entire anaesthetic drug tray pack (with cotton gauze, paper, and a plastic tray) even if using only the plastic tray, the functional unit is the entire pack and thus all component materials are accounted for. 71 A system boundary is how one defines the scope of an LCA. So, for the boundary of laryngeal mask manufacture we include the energy required to make the laryngeal mask airways (LMAs), but not the manufacture of the machines making the LMAs. 72 Second, life cycle inventories (LCIs) refer to cataloguing of materials and their associated environmental emissions. LCIs are used to understand how much those materials contribute to environmental emissions and where in the life cycle of a particular product or process those emissions occur. CO 2 e emissions are the most commonly reported environmental impact category; however, other categories exist including energy use, air, water, and soil pollutants, and ozone depletion, amongst others.

Third, life cycle impact assessment comparisons between items or systems of interest may indicate relative advantages for one outcome (e.g. CO 2 e emissions), and disadvantages elsewhere (e.g. water and terrestrial pollution). Fourth, interpreting results is essential for decision-makers. Importantly, there may be large geographic variations in the CO 2 intensity of electricity generation (g CO 2 e/kW h generated). For example, electricity produced in Europe 73 and the USA (renewables, nuclear, some coal and gas) is significantly less than that produced in China and Australia (coal dominated). 74 Thus, LCAs may be region-specific. Furthermore, results can change over time as both assessment methods and production practices change over time.

There are several types of LCAs, of which two are particularly relevant to healthcare: process-based LCAs and Environmentally Extended Economic InputeOutput (EEIO) LCAs. Process-based LCAs arrive at an environmental cost for an item or activity based upon directly measured material inputs and using LCI databases that report emissions associated with those materials. For example, recent process-based healthcare analyses of blood pressure cuffs, 75 and pathology tests 76 measured the weights, compositions, and actual use of such items in detail. Process-based LCAs tend to focus on a small, targeted, easily defined product or process and are excellent for making comparisons (e.g. reusable vs disposable equipment).

In contrast, EEIO LCAs are most appropriate when dealing with very large data sets, where it is not feasible to perform a process-based LCA (i.e. difficult to physically measure a system's material and energy inputs). EEIO LCAs rely upon nationally reported economic inputeoutput tables (e.g. via the Bureau of Economic Analysis, in the USA) and pollution emissions tables (e.g. via the US Environmental Protection Agency). 77 EEIOs attribute life cycle environmental emissions embedded in monetary value based on flows between economic sectors e that is they rely on an environmental footprint assigned to a monetary value spent. For example, a country may report its annual gross domestic product and carbon emissions arising from different economic sectors. This allows approximation of the CO 2 e emissions per monetary value spent (e.g. kg CO 2 e per $/£/V) for different economic sectors (e.g. pharmaceuticals). Approximations of entire healthcare systems' CO 2 e emissions are thus possible.

Several EEIO LCAs have been performed to estimate nationallevel healthcare sector environmental emissions. The UK Sustainable Development Unit (SDU) found that healthcare accounts for approximately 6% of England's entire CO 2 e emissions. 9 The US healthcare system contributes nearly 10% of the total US CO 2 e emissions, 77 equivalent to the CO 2 e emissions for the entire UK. 77 Australian healthcare's CO 2 e emissions (7% national total), 78 and Canada's (4% total), 79 have also been quantified. In 2019, two studies calculated that approximately 4.4e4.6% of global anthropogenic CO 2 e emissions were attributable to healthcare's activities, 7,11 excluding WAGs.

Importantly, the majority of healthcare's CO 2 e emissions (the carbon hotspots) are attributable to the procurement supply chain (everything from the purchase and discard of a plastic syringe to a new MRI scanner). 9 Further disaggregation of a national healthcare's CO 2 e emissions are most developed for the UK. 9 Medical equipment and pharmaceuticals are large CO 2 e contributors at 13% and 12% of NHS England's total CO 2 e emissions, respectively, whereas purchased electricity, gas, and direct energy use account for approximately 16%, patient (ambulance) and visitor travel 7%, and staff commuting 4%. 9 life cycle assessments in anaesthesia and critical care

Dettenkofer and colleagues 80 published the first LCAs relevant to surgery 20 yr ago, highlighting the intrinsic tension between infection prevention and environmental care. 81, 82 Much of the LCA work in anaesthesia and critical care has since focused upon comparisons between reusable and single-use equipment 72,75,83,84 with a few studies detailing emissions produced via differing surgical approaches, 85 pharmaceuticals, 86, 87 and perioperative services. 88 CO 2 e emissions associated with energy use vary considerably internationally based on the predominant energy source, for example Australia and China (coal), Europe (renewables and nuclear), 73 and the USA (mixed). 83 Whereas CO 2 e emissions of disposables depend largely upon the electricity source of manufacturing large quantities of consumables, emissions from equivalent uses of reusables largely stem from undergoing repeated cleaning. The ecological footprint of reusable medical devices depends on: the number of reuses, type of cleaning (low level or high level disinfection), sterilisation (steam or ethylene oxide), 89 and waste disposal management.

Comparisons of reusable vs single-use critical care drug trays, 71 and central venous catheter insertion kits, 89 showed that reusable equipment had the same or higher carbon footprints (in Australia). In contrast, a US study found that the carbon footprint of reusable LMAs was two-thirds that of the single-use version, 72 and the reusable rigid laryngoscope handles and blades were approximately 20 and 7 times less, respectively. 84 Similarly, a 2020 study of reusable and disposable blood pressure cuffs found that reusable cuffs were environmentally preferable to disposables, in some clinical settings by a factor of 40. 75 A review of five studies from several countries comparing reusable vs single-use surgical linens concluded that using reusables produced 50% less carbon emissions than using single-use alternatives, even in Australia, 90 because of economies of scale (washing and sterilising using large machines).

Reusable items often save money when compared with single-use equipment. 72, 75, 84 An Australian LCA comparing reusable and single use anaesthesia devices such as face masks, rigid and videolaryngoscope handles and blades, and breathing circuits 91 found that reusable equipment saved approximately AUD$5000 per operating room (OR) p.a.; however, the carbon footprint was higher (about 100 kg CO 2 e emissions per OR p.a., 91 equivalent to 800 km yr À1 driven in an average UK car). 92 If the reusables had been washed and sterilised in Europe, the carbon footprint of reusable anaesthetic equipment would have been less by 800 kg CO 2 e emissions per OR p.a. 91 (i.e. 6400 km yr À1 less driven) 92 because of different energy sources. 91 Anaesthesia breathing circuits can be used for variable periods of time in different countries, from individual patient use in the USA 93 to unclarified in Australia and New Zealand, 94 and weekly in Germany. 95 Two studies have indicated that it is as safe from a microbiological standpoint to reuse circuits, and to change and wash them weekly compared with daily. 96, 97 Several studies in the USA, including laryngoscope handles and blades, 84 LMAs, 72 and blood pressure cuffs 75 found significant cost and environmental savings from reusable devices compared with disposables.

A 2015 LCA study compared abdominal, vaginal, laparoscopic, and robotic approaches to hysterectomy, including inhaled anaesthetics and propofol. The total carbon footprint of such hysterectomies varied from approximately <10e300 kg CO 2 e emissions (i.e. equivalent to thousands of kilometres driven per operation), in large part attributable to whether the anaesthetic was inhaled vs intravenous. 92 Inhaled anaesthetic drug CO 2 e emissions comprised approximately two-thirds of the total case CO 2 e emissions for the open approaches (abdominal and vaginal-assisted) vs one-third for laparoscopic and robotic surgery. 85 life cycle assessments of active pharmaceutical ingredients (APIs) are challenging, as they require either access to confidential manufacturing practices or reverse engineering from first principals using published patents, because commercial disclosure of pharmaceutical CO 2 e emissions does not yet occur. 86, 98 A first principles approach study by Sherman and colleagues 99 found that when accounting for the entire life cycle (natural resource extraction, manufacturing, transportation, usage, and disposal), the GWPs of inhaled anaesthetics are four orders-of-magnitude greater than a minimum alveolar concentration-equivalent quantity of propofol (even accounting for plastic syringes and tubing and drug pump electricity). From the climate change perspective, TIVA is preferable to inhaled anaesthetics (especially desflurane and N 2 O). 99 Parvatker and colleagues 87 further estimated CO 2 e emissions for the API of 20 common anaesthetic/critical care drugs, finding an average 340 g CO 2 e/g API. McAlister and colleagues 86 directly observed industrial practices, estimating 2 g CO 2 e emissions/mg morphine. Almost 90% of morphine's CO 2 e emissions occurred from steam sterilisation and drug packaging, rather than the morphine API itself (0.2 g CO 2 e/mg morphine). Although there are limitations to the scaling up approach, 23 at least for morphine's associated CO 2 e emissions, there appears to be reasonable agreement with the direct study by McAlister and colleagues. 86 A study comparing the ORs of one hospital each in Canada, USA, and UK found that anaesthesia could have greater CO 2 e emissions than all surgical equipment and OR-associated energy including from heating, ventilation, and air conditioning (HVAC) combined, if desflurane were used; if not (UK hospital), then 84% CO 2 e emissions arose from the HVAC, 12% from the surgical equipment, and only 4% from anaesthetic gases (sevoflurane). 88 None of these three hospitals used N 2 O. This study by MacNeill and colleagues 88 complemented that of Sulbaek Andersen and colleagues, 25 which showed desflurane's high GWP, 21 and that of Sherman and colleagues, 99 which compared CO 2 e from clinically relevant quantities of volatile anaesthetics with propofol TIVA. Ceasing desflurane and N 2 O use would have the greatest effect in reducing the OR's carbon footprint, whilst energy efficiency efforts addressing the HVAC system and steam sterilisers would also be beneficial. 88 Pollard and colleagues 100 performed an LCA in the critical care setting, finding that an English ICU's average electricity use for direct patient care and lighting was 15 kW h patient À1 day À1 , similar to that of an average Australian four-person household. However, Pollard and colleagues 100 excluded energy for HVAC, consumables, drugs, and laboratory testing. A 2018 study examined the carbon footprint of treating ICU patients with septic shock in Australia and the USA, including HVAC, drugs, and testing using a hybrid LCA approach. 101 As the CO 2 e emissions for tests and drugs were unavailable at the time (excluding morphine), 86 only financial (EEIO) LCA accounting was possible for these elements. The CO 2 e emissions in both the USA (178 kg CO 2 e patient À1 day À1 ¼1425 km driven) and Australia (88 kg CO 2 e patient À1 day À1 ¼704 km driven), were dominated by energy use for HVAC (at least 75% of the total), with all plastics, nutrition, laundering, daily chest X-ray (CXR), 102 ventilators, and other ICU machines contributing only minor emissions. The USA's ICU had approximately double the CO 2 e emissions of the Australian ICU, attributable primarily to differences in geographical climate, with more extreme temperature variations resulting in greater HVAC energy requirements. Interestingly, there was only minor variation in patient carbon footprints according to the intensity of care (respiratory ventilation, renal support, etc.). Changing the energy sources from coal and natural gas to renewables could have the greatest effect in mitigating the ICU's carbon footprint. 101 Beyond carbon emissions CO 2 e is the most commonly reported emissions category in healthcare LCAs. As noted, there are other standard categories of pollution to air, land, and water, and including ecotoxicity, and carcinogenic and non-carcinogenic human health impacts. In the LCA finding that inhaled anaesthetic drugs were substantially less favourable than intravenous propofol from a GHG perspective, 99 the authors assumed that propofol waste was incinerated as recommended by manufacturers and health departments. Drug waste entering waterways and plastics entering landfill are also notable concerns. Approximately 50% of propofol in an operating suite can go unused. 103 Incorrect drug disposal can contribute to water contamination and toxicity. 103, 104 Improper discarding of unused propofol to the environment may have other deleterious effects upon aquatic and terrestrial ecosystems as the drug has high persistence, bioaccumulation, and toxicity. 103, 105 As multiple pollution categories exist, decision-makers must rank their import, and 'pick your poison'. 106 As climate change is an existential risk to civilisation, it is ranked as the highest LCA impact category of medium-and long-term concern. 107 Waste prevention: avoid, reduce, reuse, recycle, reprocess Operating suites produce a quarter of all hospital waste 108 (up to 25% of that from anaesthesia). 109 Critical care units are also resource intensive. 110 Waste generation seems like an inevitable outcome of treating patients. By following the waste hierarchy 111 (reduce, reuse, recycle) and adopting waste prevention programmes such as Choosing Wisely e an initiative that seeks to maintain/improve clinical care, whilst promoting rational resource use, 112 such as reducing unnecessary investigations and medications e can significantly reduce the environmental footprint of healthcare. 113 The same principles apply to avoiding medically ineffective operations and critical care admissions, or routinely opening consumables in case of an emergency. Several LCAs 77,78,98 have identified the substantial scale of pharmaceutical and medical device contributions to healthcare CO 2 e emissions, and wasted unused supplies present opportunities for pollution prevention. 114 Stock volumes could be better managed to reduce wastage, 11 whereas unused supplies may be thoughtfully donated. 115 Anaesthetists and intensivists can participate in hospital product evaluation committees and introduce LCA considerations into the procurement process, encouraging manufacturers and suppliers to provide more environmentally friendly products. 6, 116 Simple measures to reduce waste by reusing are available. Reusable equipment (metalware instruments most obviously, but also basins, gowns and drapes) remain in many areas. A broader return to reusable surgical gowns, laundered hats, and dedicated theatre footwear (removing the need for single-use overshoes) will reduce the amount of single-use clothing whilst maintaining infection control standards. As noted previously, the net environmental effect of reusable vs single-use equipment is a complex calculation, and the carbon footprint importantly depends upon the local energy source (coal/natural gas/nuclear/renewables) and efficient equipment usage. 83 Switching to a less carbon intense energy source is also a favourable solution, with health co-benefits from reduced air pollution.

If avoiding, reducing, and reusing are impossible, then recycling should be considered. 111 Approximately one-quarter of OR 117 and 15% of critical care 118 waste can be recycled. Recycling 11 tonnes of plastics, paper, etc. from a six-theatre operating suite produced approximately 15 tonnes less CO 2 e emissions p.a. 117 (120 000 km driven) 92 than the manufacture of new plastics. Recycling 1 ton of mixed plastics is equivalent to saving 16.3 barrels of oil, 30 cubic yards of landfill and 5774 kW h of energy (enough to power an average US household for 6 months). 119 Recycling of cardboard/paper and several plastic streams is not novel, but recycling of medical polyvinyl chloride (PVC) (intravenous fluid bags and oxygen masks/tubing) is less common. 120 Metals are also increasingly recycled; in 2020 'les petits doudous' (cuddly toys) recycled 9376 kg of metals including copper (electro surgical wires), stainless steel (disposable laryngoscope blades and surgical tools), and aluminium (volatile anaesthetic cans and suture thread envelopes). 121 Clinical recycling may reduce standard solid waste disposal costs by half. 117, 122 Owing to differences in the composition of critical care to OR waste, 118 and changing international markets, 123 recycling can either cost or save money.

Medical device reprocessing, or 'remanufacturing', refers to cleaning and packaging of single-use equipment for reuse 124 and may save money and emissions. 125 Examples of reprocessed devices include surgical staplers, blood pressure and calf compressor cuffs, and cardiological catheters. 124 This is a multibillion dollar industry in the USA 124 and now occurs in many countries e 28% of hospitals in Canada, 126 40% in Germany, 80% in Spain and 80e90% in Japan. 127 In other countries, for example Australia and France, reprocessing is not yet approved, although regulatory changes are under consideration in the UK.

Energy is the basis of much of our work's carbon footprint. Research on healthcare architecture and infrastructure is at a much more mature stage than how clinicians deliver healthcare. 128, 129 Through sustainable healthcare architectural design, construction, and operations, environmental emissions can be reduced, 128 while patient well-being and staff satisfaction are improved. Quiet surroundings, natural lighting, and views or contact with nature improve patient recovery. 130 The costs of constructing a more ecologically friendly indoor healthcare environment may also be offset by happier, healthier staff. 128 Infrastructure planning should recognise the interdependence of economic, social, and environmental benefits. 128, 130 Workplace efficiency reduces waste, energy, and costs; hence new and existing facilities could be designed or retrofitted to reduce wastage of natural resources.

Collaboration between hospital engineers and anaesthetists/intensivists could assist in improving OR/critical care engineering efficiencies and innovation. 131, 132 Evidence to support why OR and critical care HVAC settings exchange room air 20 and 6 times per hour, respectively, is lacking. Unoccupied ORs need not undergo 20 air changes h À1 ; Table 1 Research base for the environmental impact of anaesthesia and intensive care. GWP, global warming potential; HVAC, heating, ventilation, and air conditioning; LCA, life cycle assessment; LMA, laryngeal mask airway; TIVA, total intravenous anaesthesia.

Evidence and uncertainties Gases Avoid, where possible, the use of anaesthetic gases with high GWP and minimise amount used of all anaesthetic gases.

Known: Avoid the use of desflurane and nitrous oxide. 99 The GWPs of anaesthetic gases are well researched. Encourage low flow and automated end tidal control anaesthesia. 49 Uncertain: What is the worldwide use of anaesthetic gases/TIVA and how is this evolving? Waste anaesthetic gas reclamation research is emerging, though currently rare clinically. 40 What are the environmental effects of medical use of O 2 /air? TIVA Known: TIVA (propofol) itself has approximately 1% the GWP of even sevoflurane volatile anaesthesia. 87, 99 Uncertain: TIVA's other environmental effects. Quantification of water contamination from anaesthetic pharmaceuticals. Balancing TIVA's plastic waste, etc. with the GWPs of volatiles.

Uncertain: What is the environmental footprint of regional anaesthesia? Are there trade-offs between the carbon footprint and other environmental effects?

Known: The carbon footprint of machines for treating 100 setbacks are readily feasible without leading to an increase in microbiological contamination. 133 Furthermore, hospitals can transition to more renewable energy sources, to considerably reduce CO 2 e emissions and air pollution; however, such efforts require persistence and effort.

Large amounts of water in hospitals are used for routine patient care (taps, baths, showers), air conditioning systems, or in specialised areas (e.g. dialysis). 134, 135 Almost 20 L of water is used for each surgical handwash at manually operated sinks, whereas motion sensors could dramatically reduce this volume. Future ecological comparisons may consider water-based handwash with alcohol/chlorhexidine-based hand rub. 136 Similarly, almost 1000 L of water are used for each cycle of a large hospital steam steriliser, 137 with considerable savings possible through more efficient steriliser usage. 138 Recently, in times of drought, reducing direct water requirements to clean and sterilise reusable devices has often been ranked of greater short-term importance than reducing one's carbon footprint through avoidance of singleuse devices. 139 Further, as freshwater itself becomes scarcer, there are increasing monetary value and CO 2 e emissions attached to alternative sources such as through desalination. 138 Travel Considerable health benefits arise from less fossil-fuelled travel, both active and public transport. 140, 141 Fewer 'carbon miles' reduces the public health burden of climate change and air pollution. 142 Greater active transport have health cobenefits through increasing physical activity, lowers rates of obesity, diabetes, and cardiovascular disease. Some preadmission appointments, for example could be performed remotely using telehealth methods. Anaesthetists and critical care physicians should be aware of the benefits of teleconferencing on the environment and health, 143 and also on academic and administrative meetings. 144, 145 Education and advocacy

Multiple anaesthesia organisations now have advocacy statements about environmentally sustainable practices (e.g. USA, 146 UK, 147 France, 148 Canada, 149 Europe, 150 and Australia/ New Zealand. 43, 151 Interest in environmental sustainability is also evident within anaesthesia editorials in British Journal of Anaestheisa, 35 Anesthesia and Analgesia, 152, 153 Anaesthesia, 154, 155 Canadian Journal of Anesthesia, 156 and Anaesthesia Critical Care and Pain Medicine. 157 Educational publications within anaesthesia journals, particularly describing climate change and the atmospheric effects of anaesthetic gases exist. 35, 40, 47 Such 'ecological interest' has also been demonstrated through anaesthetist professional surveys, 42, 158 but is currently rare in intensive care medicine, 159 scientific meetings, and societies/ colleges. 160 Similarly, the link between the environmental and social pillars of sustainable development (Planet, Profit, and People) requires promulgation. 161 Often by improving workplace environmental (and financial) sustainability, social sustainability will also be improved in a 'virtuous cycle'. 162 For example through greater recycling of metalwork and plastics in French paediatric ORs, environmental and financial savings were achieved, staff felt positive about their actions, and toys were purchased for sick children with the recycling proceeds. 81 Importantly, behavioural change is possible, and 'social tipping points' will indeed be necessary to achieve rapid reductions in the transition to a low-carbon world. 163 Conclusions Healthcare itself pollutes. 6 Anaesthesia and critical care are the cause for a considerable contribution to such healthcare pollution. We recognise that there can be accord and conflict between individual patient health and public health commitments, particularly in the field of infection prevention, 164 although one can protect the patient and the planet. 81 Over the past decade considerable progress has been made in improving the research foundation of environmentally sustainable healthcare, a summary of evidence pertaining to anaesthesia and critical care can be found in Table 1 . Such considerations do not usurp patient-centred nor fiscally prudent care, but rather complement such goals by protecting patients, our healthcare system, and the environment. 81

All authors contributed to the writing of this review article. FM conceived, wrote, revised, and edited the article. JM, CL, and JDS revised and edited the article. 

The Lancet Countdown on health and climate change: from 25 years of inaction to a global transformation for public health

Global warming of 1.5 C: an IPCC special report on the impacts of global warming of 1.5 C above pre-industrial levels and related global greenhouse gas emission pathways. In: The context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty

Signs of the planet. fourth warmest year in continued warming trend, according to NASA

Managing the health effects of climate change

How will country-based mitigation measures influence the course of the COVID-19 epidemic?

Reducing pollution from the health care industry

International comparison of health care carbon footprints

Report of the World Commission on environment and development: our common future

Towards sustainable development: IV. Conclusion. Available from 1987

Reducing the use of natural resources in health and social care

NHS Sustainable Development Unit study report

The 2019 report of the Lancet Countdown on health and climate change: ensuring that the health of a child born today is not defined by a changing climate

Joseph Fourier, the 'greenhouse effect', and the quest for a universal theory of terrestrial temperatures

IPCC (Intergovernmental Panel on Climate Change). The physical science basis. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change

The role of HFCs in mitigating 21st century climate change

WMO greenhouse gas bulletin World Meteorological Organization. The state of greenhouse gases in the atmosphere based on global observations

Nitrous oxide (N 2 O): the dominant ozone-depleting substance emitted in the 21st century

Greenhouse gas molecules: a mathematical perspective

A first course in atmospheric radiation

Inhalation anaesthetics and climate change

Global warming potential of inhaled anesthetics: application to clinical use

Atmospheric chemistry of isoflurane, desflurane, and sevoflurane: kinetics and mechanisms of reactions with chlorine atoms and OH radicals and global warming potentials

Tropospheric lifetimes of halogenated anaesthetics

Short-term variations in the oxidizing power of the atmosphere

Chemical kinetics and photochemical data for use in atmospheric studies, evaluation number 14

Assessing the impact on global climate from general anesthetic gases

Volatile anaesthetics and the atmosphere: atmospheric lifetimes and atmospheric effects of halothane, enflurane, isoflurane, desflurane and sevoflurane

Atmospheric chemistry of methoxyflurane (CH 3 OCF 2 CHC l2 ): kinetics of the gas-phase reactions with OH radicals, Cl atoms and O 3

Modern inhalation anesthetics: potent greenhouse gases in the global atmosphere

Abandoning inhalational anaesthesia

Inhalational anaesthesia market size share & trends analysis report by application (induction, maintenance), by product (Sevoflurane, Isoflurane, Desflurane), by region, and segment forecasts

A different perspective on anesthetics and climate change response

Nitrous oxide and the greenhouse effect

General anesthetic gases and the global environment

Anaesthetic_gases_ research_v1.pdf

Atmospheric science, anaesthesia, and the environment

The United Nations Environment. Environmental rights and governance. Montreal Protocol

United Nations Framework Convention on Climate Change. The Paris agreement

Do hydrofluorocarbons destroy stratospheric ozone?

Environmental impacts of nitrous oxide: no laughing matter! Comment on

Reducing inhaled anaesthetic waste and pollution Anaesthesiology News

com/Commentary/Article/04-17/Reducing-Inhaled-Anesthetic-Waste-and-Pollution/40910

A long way to go: minimizing the carbon footprint from anesthetic gases

A survey of the choice of general anaesthetic agents in Australia and New Zealand

Why be sustainable? The Australian and New Zealand college of anaesthetists professional document PS64: statement on environmental sustainability in anaesthesia and Pain medicine practice and its accompanying background paper

Why anaesthetists should no longer use nitrous oxide

Greening the operating room and perioperative arena: environmental sustainability for anesthesia practice

Inhaled anesthesia climate initiative: project drawdown inhaled anesthetic 2020 challenge

Environment. Why it matters. Anaesthetic gases calculator

The quantitative practice of anesthesia use of closed circuit

Managing fresh gas flow to reduce environmental contamination

The volatile consumption: uptake ratio as a measure of the efficiency of semi-closed circle breathing system usage

There are no dragons: low-flow anaesthesia with sevoflurane is safe

Low-flow sevoflurane compared with low-flow isoflurane anesthesia in patients with stable renal insufficiency

Estimating the impact of carbon dioxide absorbent performance differences on absorbent cost during low-flow anesthesia

In vitro efficiency of 16 different Ca(OH) 2 based CO 2 absorbent brands

The reduction of pollution. A simple approach to the reduction of pollution in the dental operating theatre

Use of the AnaConDa (anesthesia conserving device) with sevoflurane in critical care patients: a-708

A new structural family of gas-sorbing coordination polymers derived from phenolic carboxylic acids

Bluezone anesthetic collection service

Silica zeolite scavenging of exhaled isoflurane: a preliminary report

capturing-utilization-and-reduction/ destruction-of-medical-n2o-in-sweden

Tunable porous coordination polymers for the capture, recovery and storage of inhalation anesthetics

Removal of sevoflurane and nitrous oxide from waste anesthetic gases by using Anesclean, the system for treating waste anesthetic gases

New method of destroying waste anesthetic gases using gas-phase photochemistry

Next-generation CO 2 removal for anesthesia circuits

An initial evaluation of a novel anesthetic scavenging interface

Reclaiming waste anesthetic gas: initial clinical trials: 3AP8-3

The ecoinvent database: overview and methodological framework

Life cycle costing in LCM: ambitions, opportunities, and limitations

International Organization for Standardization

The financial and environmental costs of reusable and single-use plastic anaesthetic drug trays

Comparative life cycle assessment of disposable and reusable laryngeal mask airways

EU greenhouse gas inventory

Ecoinvent d the world's most consistent & transparent life cycle inventory database

Environmental and economic comparison of reusable and disposable blood pressure cuffs in multiple clinical settings

The carbon footprint of pathology testing

Environmental impacts of the US health care system and effects on public health

The carbon footprint of Australian health care

Life cycle environmental emissions and health damages from the Canadian healthcare system: an economiceenvironmentaleepidemiological analysis

Life-cycle assessment of single-use versus reusable surgical drapes (cellulose/polyethylene-mixed cotton system)

Protecting the patient and the environmentdnew aspects and challenges in hospital infection control

Environmental auditing in hospitals: approach and implementation in a university hospital

Workplace sustainability: the "cradle to grave" view of what we do

Life cycle assessment and costing methods for device procurement: comparing reusable and single-use disposable laryngoscopes

Environmental impacts of surgical procedures: life cycle assessment of hysterectomy in the US

The Environmental footprint of morphine: a life cycle assessment from opium poppy farming to the packaged drug

Cradleto-gate greenhouse gas emissions for twenty anesthetic active pharmaceutical ingredients based on process scale-up and process design calculations

The impact of surgery on global climate: a carbon footprinting study of operating theatres in three health systems

A life cycle assessment of reusable and single-use central venous catheter insertion kits

A comparison of reusable and disposable perioperative textiles: sustainability state-of-the-art 2012

Financial and environmental costs of reusable and single-use anaesthetic equipment

Guidelines for preventing healthcare associated pneumonia. Recommendations of CDC and the healthcare infection control practices advisory committee

guidelines-on-infection-control-in-anaesthesia. pdf/view?searchterm¼guidelines%20on%20infection %20control

Infection prevention during anaesthesia ventilation by the use of breathing system filters (BSF): joint recommendation by German Society of Hospital Hygiene (DGKH) and German Society for Anaesthesiology and Intensive Care (DGAI)

The microbiological and sustainability effects of washing anaesthesia breathing circuits less frequently

Bacterial and viral contamination of breathing circuits after extended useean aspect of patient safety?

Sustainable Development Unit. reportNHS sustainable development unit. Carbon hotspots report

Life cycle greenhouse gas emissions of anesthetic drugs

The carbon footprint of acute care: how energy intensive is critical care?

The carbon footprint of treating patients with septic shock in the intensive care unit

Energy efficiency in hospitals and laboratories

Propofol wastage in anesthesia

Drug waste harms fish

Environmentally classified pharmaceuticals

Total intravenous anesthetic versus inhaled anesthetic: pick your poison

Life cycle impact assessment weights to support environmentally LCAs in anaesthesia and critical care -11

the United States

Greening the operating room and perioperative arena: environmental sustainability for anesthesia practice

An audit of potentially recyclable waste from anaesthetic practice

An audit of intensive care unit recyclable waste

Life cycle assessment of energy from solid waste d part 1: general methodology and results

Choosing wisely: helping physicians and patients make smart decisions about their care

The Sustainable Development Unit UK. Identifying high greenhouse gas intensity prescription items for NHS in England

Cataract surgery and environmental sustainability: waste and lifecycle assessment of phacoemulsification at a private healthcare facility

Cost-effective use of operating room supplies based on the REMEDY database of recovered unused materials

Environmental sustainability in anesthesia

Auditing operating room recycling: a management case report

Auditing an intensive care unit recycling program

Telling the story: how to effectively communicate your hospital recycling program's successes and lessons learned

The Vinyl Council of Australia. PVC recovery in hospitals

Les petits doudous: le recyclage (the cuddly toy: recycling). Available from

The gold in garbage: implementing a waste segregation and recycling initiative

The world is scrambling now that China is refusing to be a trash dumping ground

Commentary: a call to go green in health care by reprocessing medical equipment

Assessing the environmental, human health, and economic impacts of reprocessed medical devices in a Phoenix hospital's supply chain

The ethics of reusing single-use devices

What is the use? An international look at reuse of single-use medical devices

Sustainable healthcare architecture

Environmental sustainability in hospitals e a systematic review and research agenda

Green healthcare institutions; health, environment and economics (workshop summary)

Risk management: where are hospital 'green' committees and officers?

Trends in green hospital engineering

Shutting down operating theater ventilation when the theater is not in use: infection control and environmental aspects

Recycling wastewater after hemodialysis: an environmental analysis for alternative water sources in arid regions

Using water wisely: new, affordable, and essential water conservation practices for facility and home hemodialysis

Clean and green: saving water in the operating theatre

Steam sterilisation's energy and water footprint

Hospital steam sterilizer usage: could we switch off to save electricity and water?

Response to 'Healthcare and ecological economics at a crossroads'

Environmental aspects of health care in the Grampian NHS region and the place of telehealth

Estimates and 25-year trends of the global burden of disease attributable to ambient air pollution: an analysis of data from the Global Burden of Diseases Study

The impact of telemedicine on greenhouse gas emissions at an academic health science center in Canada

Carbon-neutral medical conferences should be the norm

The International Society for Children's Health and the Environment commits to reduce its carbon footprint to safeguard children's health

The American Society of Anesthesiologists

Environmental Policy Statement d FINAL.pdf?

Guide pratique du d eveloppement durable au bloc op eratoire

Royal College of Physicians and Surgeons of Canada. CanMEDS

Statement on environmental sustainability in anaesthesia and pain medicine practice

Sustainable anesthesia

The perioperative garden of Eden: leading edge or trailing edge?

The anaesthetist and the environment

A new role for anaesthetists in environmentally-sustainable healthcare

Greenhouse gases: the choice of volatile anesthetic does matter

Why should anaesthesiologists and intensivists care about climate change?

A survey of the American Society of Anesthesiologists regarding environmental attitudes, knowledge, and organization

Greening critical care

The social pillar of sustainable development: a literature review and framework for policy analysis

How healthy is health care?

Social tipping dynamics for stabilizing Earth's climate by 2050

Balancing infection control and environmental protection as a matter of patient safety: the case of laryngoscope handles

Association of Anaesthetists of Great Britain and Ireland (AAGBI)

Recovered medical equipment for the developing world

The sustainable development unit UK

Global green and healthy hospitals

The Climate and Health Alliance (CAHA)

Doctors For the environment

Jonathan Hardman LCAs in anaesthesia and critical