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Environmental impacts of nitrous oxide: no laughing matter! Comment on Br J Anaesth 2019; 122: 587–604

2019; Elsevier BV; Volume: 123; Issue: 4 Linguagem: Inglês

10.1016/j.bja.2019.06.013

1471-6771

Jane Muret, Tiago Fernandes, Herwig Gerlach, Georgina Imberger, Henrik Jörnvall, Cathy Lawson, Forbes McGain, Frances Mortimer, Jean-Claude Pauchard, Tom Pierce, Samantha Shinde, Frank Swinton, Lucy Williams,

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Editor—We thank Buhre and colleagues1Buhre W. Disma N. Hendrickx J. et al.European society of anaesthesiology task force on nitrous oxide: a narrative review of its role in clinical practice.Br J Anaesth. 2019; 122: 587-604Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar for their contemporary review of the place for nitrous oxide (N2O) in current clinical practice, particularly for noting the existence of environmental toxicity concerns. We feel, however, that the authors did not adequately assess or communicate the environmental impact of N2O use, and we are concerned by the conclusion that the 'perceived environmental drawbacks … have been exaggerated or misplaced'. Whilst medical sources of N2O are minor compared with forest destruction, pollution from vehicles, and nitrogen fertilisers, they are not irrelevant and contribute to greenhouse gas accumulation that is accelerating climate change. There is an essential connection between environmental disorders and human health. As physicians, we need to recognise the contributions of our healthcare system to climate change. Rather than looking for ways to argue that our contributions to greenhouse gas emissions are not significant,2Sherman J. Barrick B. Total intravenous anesthetic versus inhaled anesthetic pick your poison.Anesth Analg. 2019; 128: 13-15PubMed Google Scholar we should be systematic and objective in our assessment of the environmental effects of medical interventions, and should look for ways that we can contribute to the pressing carbon dioxide equivalent emission (CO2e) reduction targets set by national governments and international treaties. In their summary, Buhre and colleagues1Buhre W. Disma N. Hendrickx J. et al.European society of anaesthesiology task force on nitrous oxide: a narrative review of its role in clinical practice.Br J Anaesth. 2019; 122: 587-604Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar claim that they describe current knowledge based on a systematic and critical analysis of the scientific literature. In their Table 1, they provide Grading of Recommendations Assessment, Development and Evaluation (GRADE) evidence levels for major adverse clinical effects.1Buhre W. Disma N. Hendrickx J. et al.European society of anaesthesiology task force on nitrous oxide: a narrative review of its role in clinical practice.Br J Anaesth. 2019; 122: 587-604Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar The authors have included atmospheric pollution as a clinical effect and assigned the 'evidence level' B, equating to the assessment that 'further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate'. We disagree with the classification of atmospheric pollution as a clinical effect. However, atmospheric pollution indirectly causes harm to human health: climate change attributable to greenhouse gas accumulation generates extreme events such as flooding, drought, heat waves, and trapping of ground level air pollutants resulting in increased cardiovascular events such as myocardial infarction and stroke, asthma, and chronic lung disease exacerbation, etc. These effects on the health of populations could represent the 'biggest global health threat of the 21st century'.3The Lancet, Health and Climate Change Commission. Available from www.thelancet.com/commissions/climate-change (Accessed 7 November 2019).Google Scholar We also challenge that an objective and systematic assessment of the evidence associating N2O with atmospheric pollution would produce a GRADE evidence level grade B. The global warming potential (GWP100) of N2O is 298 times that of CO2.4Forster P. Ramaswamy V. Artaxo P. et al.Changes in atmospheric constituents and in radiative forcing.in: Solomon S. Qin D. Manning M. Climate change 2007: the physical science basis. Contribution of working group I to the fourth assessment report of the intergovernmental panel on climate change. Cambridge University Press, Cambridge, UK and NY, USA2007: 212Google Scholar Thus, a 50% mix of N2O and oxygen with a fresh gas flow (FGF) of 1 L min−1 equates (at 25°C) to (0.5×1 L min−1×60 min/24.8 L mol−1)×44.0 g mol−1=53.2 g of N2O h−1. The GWP100 of 1 h of 50% N2O at a FGF of 1 L min−1 is 53.2 g×298=15.8 kg of CO2. Or, to use an analogy from daily life, the equivalent of driving an average European car 120 km!5CO2 Car Emissions. Available from http://www.carpages.co.uk/co2/ (Accessed 7 November 2019).Google Scholar As a profession, we should not neglect the greenhouse potential equivalent of driving almost 1000 km during an 8 h working day. The greenhouse potential of sevoflurane used in the same manner is small in comparison, and can be made negligible by using lower FGFs. The NHS Sustainable Development Unit 2012 Carbon Footprint from Anaesthetic Gas Use reports that total emissions for anaesthetic gases including N2O represents 2.5% of the UK footprint, and that more than 50% of that comes from N2O.6NHS Sustainable Development Unit, Carbon Footprint from Anaesthetic Gas Use. Available from http://www.sduhealth.org.uk/documents/publications/Anaesthetic_gases_research_v1.pdf (Accessed 7 November 2019).Google Scholar The recently published NHS long-term plan requires reducing the CO2e of inhaled anaesthetic practice by at least 210 000 tonnes (T) per annum in order to achieve NHS Climate Change Act targets. Of the current annual total 470 000 T CO2e from anaesthetic practice, volatile anaesthetics account for approximately 100 000 T, surgical use of N2O for 100 000 T, and non-surgical use (in maternity and emergency care) a further 270 000 T (J. Baddley, personal communication, NHS Sustainable Development Unit). In reality, a reduction in the carbon footprint of anaesthesia can only be achieved by significantly reducing the use of N2O. We agree that modern anaesthesia work stations, scavenging systems, or both (Karolinska Hospital, Stockholm) have the potential to minimise the environmental effects of inhalation anaesthesia, but this would imply an enormous investment for each single healthcare provider and will delay by years the reduction of anaesthesia carbon footprint. Further, because of the large alveolar uptake of N2O, it remains a challenge to use extremely low fresh gas flows or closed-circuit anaesthesia with N2O. In the meantime, N2O should be regarded by anaesthetists as one of the three worrying, potent Kyoto non-CO2 greenhouse gases along with methane and hydrofluorocarbons. N2O and desflurane have similar (high) global warming effects when used clinically.7Sherman J. Le C. Lamers V. Eckelman M. Life cycle greenhouse gas emissions of anesthetic drugs.Anesth Analg. 2012; 114: 1086-1090Crossref PubMed Scopus (194) Google Scholar Further, N2O is the major cause of ongoing ozone depletion.8Ravishankara A. Daniel J.S. Portmann R.W. Nitrous oxide (N2O): the dominant ozone-depleting substance emitted in the 21st century.Science. 2009; 326: 123-125Crossref PubMed Scopus (3077) Google Scholar Avoidance of N2O by anaesthetists will likely make the largest contribution to reducing anaesthetic greenhouse gas emissions. To play our part in reducing contributions to environmental toxicity, the important question is: are there less atmospherically damaging alternatives to N2O that are readily available to safely anaesthetise patients? We suggest that a systemic and objective assessment of relevant evidence would lead to a clear and evidence-level-A answer of Yes. FMcG has received research grant funding from the Australian and New Zealand College of Anaesthetists, Australia, (2018/011) examining ways to destroy/capture anaesthetic gases. All of this grant funding has gone to assist other associate investigators and equipment purchases. The other authors declare no conflicts of interest. European Society of Anaesthesiology Task Force on Nitrous Oxide: a narrative review of its role in clinical practiceBritish Journal of AnaesthesiaVol. 122Issue 5PreviewNitrous oxide (N2O) is one of the oldest drugs still in use in medicine. Despite its superior pharmacokinetic properties, controversy remains over its continued use in clinical practice, reflecting in part significant improvements in the pharmacology of other anaesthetic agents and developing awareness of its shortcomings. This narrative review describes current knowledge regarding the clinical use of N2O based on a systematic and critical analysis of the available scientific literature. The pharmacological properties of N2O are reviewed in detail along with current evidence for the indications and contraindications of this drug in specific settings, both in perioperative care and in procedural sedation. Full-Text PDF Open ArchiveResponse to comments on 'The European Society of Anaesthesiology Task Force review on the place of nitrous oxide in current clinical practice' (Br J Anaesth 2019; 122:587–604)British Journal of AnaesthesiaVol. 123Issue 4PreviewEditor—We thank Imberger and McGain1 and Muret and colleagues2 for their interest in our review3 of the place of N2O in clinical practice and their comments. The primary focus of our review was on the clinical utility of N2O and its risk–benefit in clinical practice. However, given the broader context of climate change and the known contribution of greenhouse gases to global warming, we felt it would have been inappropriate to fail to include atmospheric pollution in the list of drawbacks of N2O, which we believe has been a major contributor to the decline in its routine use in anaesthesia. Full-Text PDF Open ArchiveUse of the GRADE approach in systematic reviews and guidelinesBritish Journal of AnaesthesiaVol. 123Issue 5PreviewThe Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach is a systematic and transparent approach for rating the certainty of evidence in systematic reviews and clinical practice guidelines, and for developing and determining the strength of clinical practice recommendations.1 While use of GRADE in systematic reviews is currently only mandated by a few (∼4%) journals within anaesthesia and intensive care medicine,2 it is becoming a de facto standard for high-quality systematic reviews, and it is an essential component of trustworthy guidelines. Full-Text PDF Open Archive