Portal de Periódicos da CAPES

Quantitative nitrous oxide usage by different specialties and current patterns of use in a single hospital

2022; Elsevier BV; Volume: 129; Issue: 3 Linguagem: Inglês

10.1016/j.bja.2022.05.022

1471-6771

Angela Wong, Alice Gynther, Christine Li, Max Rounds, Jung H. Lee, David Krieser, Elske Posma, Forbes McGain,

Cardiac, Anesthesia and Surgical Outcomes

Editor—Nitrous oxide (N2O) is widely used in birthing suites, operating theatres, and paediatric units.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 (49) Google Scholar Recent evidence has shown that the volume of N2O purchased can considerably exceed what is used clinically.2Chakera A. Fennell-Wells A. Allen A. Nitrous oxide project: piped nitrous oxide waste reduction strategy. Association of Anaesthetists, 2021 Jan 15https://anaesthetists.org/Home/Resources-publications/Environment/Nitrous-oxide-projectGoogle Scholar, 3Chakera A. Waite A. Marchant A. Baldie C. Establishing system waste of piped nitrous oxide; Lothian nitrous oxide mitigation project. Anaesthesia annual congress virtual conference.https://doi.org/10.1111/anae.15578Date: 2021 September 23–24Google Scholar, 4Seglenieks R. Wong A. Pearson F. McGain F. Discrepancy between procurement and clinical use of nitrous oxide: waste not, want not.Br J Anaesth. 2022; 128: e32-e34Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar This may be attributable to leaks, residual N2O left in cylinders, theft,3Chakera A. Waite A. Marchant A. Baldie C. Establishing system waste of piped nitrous oxide; Lothian nitrous oxide mitigation project. Anaesthesia annual congress virtual conference.https://doi.org/10.1111/anae.15578Date: 2021 September 23–24Google Scholar or (less likely) estimation error. This difference between purchased and patient-used N2O is a subtype of N2O wastage, referred to hereafter as discrepancy. As N2O is a potent greenhouse gas and contributes to ozone layer depletion, measuring and reducing this discrepancy has important environmental benefits beyond financial and social.5Tennison I. Roschnik S. Ashby B. et al.Health care's response to climate change: a carbon footprint assessment of the NHS in England.Lancet Planet Health. 2021; 5: e84-e92Abstract Full Text Full Text PDF PubMed Scopus (182) Google Scholar,6McGain F. Muret J. Lawson C. Sherman J.D. Environmental sustainability in anaesthesia and critical care.Br J Anaesth. 2020; 125: 680-692Abstract Full Text Full Text PDF PubMed Scopus (108) Google Scholar Studies in the UK have shown N2O discrepancy can be as high as 95% of the purchased volume,7Chakera A. Nix the nitrous.2021https://www.greenhealthwales.co.uk/post/nix-the-nitrousGoogle Scholar and a hospital in our health network in Australia found this discrepancy to be 77%.4Seglenieks R. Wong A. Pearson F. McGain F. Discrepancy between procurement and clinical use of nitrous oxide: waste not, want not.Br J Anaesth. 2022; 128: e32-e34Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar When manifold N2O supplies solely operating theatres, where cumulative patient-used N2O is captured by anaesthetic machines, it is relatively easy to estimate this discrepancy. Conversely, it is considerably more challenging to estimate discrepancy when the N2O manifold also supplies multiple different clinical specialty areas. Being able to clearly distinguish between patient-used N2O and purchased N2O to estimate discrepancy is integral to aid mitigation strategies and influence changes at a hospital level. To this end, we modified the sleeves of a portable flow meter (Fig 1), and sequentially measured our hospital's main areas of N2O use: (1) operating theatres, (2) birthing suite, and (3) paediatric emergency department (PED). Our study ran from 2020 to 2021, approved by the Western Health Ethics Committee (QA 2020.53/ERM 6842), with patient consent waived. Our measurement of patient-used N2O (notably not purchased N2O) found that amounts used per month were as follows: (1) 3000 L in all 13 operating theatres (using anaesthetic machines) for 1617 theatre cases; in one frequently used birthing room for all labour types, out of 21 total rooms in the Birthing Suite (Maternity), it was 8543 L (16 parturients out of 39 in that room used N2O) for 423 total labouring women in the entire birth suite; and (3) 5037 L in one entire PED for 1736 cases. These data demonstrate maternity as the highest user of N2O despite serving the lowest population of patients, so N2O mitigation efforts would have the highest impact in the maternity group. We continued evaluating N2O practice in our hospital. N2O events (episodes where N2O was used for a patient) were collected using a variety of sources according to the different clinical areas and specialties to derive patient-used N2O per case. This included: (1) a prospective audit filled by anaesthetists in theatre each time N2O was used (3000 L divided by 62 N2O events), that is 48 L N2O used per theatre case, and a N2O event rate (N2O usage event divided by total theatre cases) of 3.5%; (2) retrospective Birthing Suite audit of a single birthing room (8543 L divided by 16 N2O events), that is 534 L N2O used per labour, and a total hospital electronic medical record audit finding a N2O event rate (total N2O events divided by total labours) of 62%; and (3) retrospective PED audit of hospital electronic medical records (5037 L divided by 82 N2O events), that is. 61 L N2O used per PED procedure, and a N2O event rate (total N2O events divided by total presentations) of 4%. The average total purchased N2O per month was 186 600 L. The projected total patient-used N2O per month of: (1) 2717 L in entire operating suite (3.5%×1617×48), (2) 140 047 L in entire birthing suite (62%×423×534), and (3) 4236 L N2O in entire PED (4%×1736×61), summed to 147 000 L. This left 21% (39 600 L N2O) unaccounted for, which is a significant discrepancy. This finding has initiated conversations and actions in investigating for causes of this discrepancy between patient-used and purchased N2O from engineering, bioengineering, pharmacy, and clinical staff at our hospital, which were previously passive observers of N2O use. Although preliminary investigations (leak and pressure testing) have not revealed an obvious leak in the hospital's N2O delivery system, these tests are imperfect, as evidenced by a New Zealand hospital experience.8Chakera A, Jenks M, Burrell R. N2O or not? Environmental sustainability network (ESN), Australian New Zealand college of anaesthetists (ANZCA) webinar 2022 march 15. [cited 2022 March 15]. Available from: https://vimeo.com/690720448/5a6d8f7ab6.Google Scholar A subtle – rather than a large – leak may explain the 21% discrepancy not being higher, unlike prior studies.2Chakera A. Fennell-Wells A. Allen A. Nitrous oxide project: piped nitrous oxide waste reduction strategy. Association of Anaesthetists, 2021 Jan 15https://anaesthetists.org/Home/Resources-publications/Environment/Nitrous-oxide-projectGoogle Scholar, 3Chakera A. Waite A. Marchant A. Baldie C. Establishing system waste of piped nitrous oxide; Lothian nitrous oxide mitigation project. Anaesthesia annual congress virtual conference.https://doi.org/10.1111/anae.15578Date: 2021 September 23–24Google Scholar, 4Seglenieks R. Wong A. Pearson F. McGain F. Discrepancy between procurement and clinical use of nitrous oxide: waste not, want not.Br J Anaesth. 2022; 128: e32-e34Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar The large maternity N2O use would also reduce the discrepancy percentage (although not the absolute volume). Sunshine Hospital's N2O manifold is 33 yr old, with the hospital providing all inpatient services except for cardiac surgery and neurosurgery. There are variations in N2O practice and infrastructure in different hospitals worldwide. However, there are also many healthcare centres similar to ours where a N2O manifold and its pipelines supply multiple different clinical areas without anaesthetic machines, where quantification of actual clinical use is unmonitored, challenging, and discrepancy from procurement remains unknown. This is not an isolated problem; thus our N2O measuring method has wider applicability. Results from our flow meter measured maternity use of N2O were considerable at 534 L N2O for each labour. Our study complements findings from previous estimations of medical N2O use relying upon other methods.5Tennison I. Roschnik S. Ashby B. et al.Health care's response to climate change: a carbon footprint assessment of the NHS in England.Lancet Planet Health. 2021; 5: e84-e92Abstract Full Text Full Text PDF PubMed Scopus (182) Google Scholar,9Martindale T. Pierce J.M.T. Brocke C. Letters to the editor: the CO2e of inhalational anaesthetic use in a University Hospital; suggestions for continued progressive reductions.Br J Anaesth eLetters Suppl. 2016; 117https://doi.org/10.1093/bja/el_13932Abstract Full Text Full Text PDF Scopus (3) Google Scholar, 10Elliott K.J. Pierce J.M.T. Twelve-year trend in nitrous oxide use at a tertiary institution: striving for a net zero NHS.Anaesthesia. 2021; 76: 1667-1668Crossref PubMed Scopus (1) Google Scholar, 11Ek M. Tjus K. Decreased emission of nitrous oxide from delivery wards—case study in Sweden.Mitig Adapt Strateg Glob Change. 2008; 13: 809-818Crossref Scopus (9) Google Scholar To achieve the projected total patient-used N2O in the Birthing Suite, we extrapolated findings from a single birthing room to all N2O-facilitated labours in the Birthing Suite. Although this is a limitation, the alternatives (cutting into N2O pipelines or having 21 portable flow meters) would have been impractical. Our study introduces a method of measuring clinical N2O use in the absence of an anaesthesia machine that is relatively affordable, shareable between different clinical areas and even health facilities. Our method is important in order to confirm and track the presence of discrepancy (i.e. wasted N2O) and raise awareness of this issue at a local hospital level. The measured findings of different N2O usage between specialties also better informs where future targets for N2O mitigation should be focused, given that N2O is a healthcare carbon hotspot.5Tennison I. Roschnik S. Ashby B. et al.Health care's response to climate change: a carbon footprint assessment of the NHS in England.Lancet Planet Health. 2021; 5: e84-e92Abstract Full Text Full Text PDF PubMed Scopus (182) Google Scholar We thank A.J. Tagg, D. Heelan, and F. Smith from Western Health, Melbourne, Australia, for their assistance. FM and AG are members of Doctors for the Environment Australia. All other authors have declared no conflicts of interest.