Reducing carbon emissions: One gas at a time

Nitrous oxide (N2O) is the biggest contributor to carbon emissions of all the anaesthetic gases [1]. Data from the recent National Audit Project show that N2O is commonly used for paediatric induction and anaesthesia maintenance in the UK [2]. Within our hospital, size G N2O cylinders are operated on a manifold system to supply the dental suite, paediatric and obstetric theatres. Entonox is supplied by pipeline or portable cylinder use. Changes in service delivery during the COVID-19 pandemic provided us with a unique opportunity to examine the relationship between anaesthetic caseload and N2O use. Methods The clinical areas receiving pipeline N2O were identified. Elective paediatric theatre, dental sedation cases and obstetric deliveries were audited retrospectively from April 2018 to April 2021. We then examined the relationship between caseload and N2O/Entonox consumption. Results Monthly elective paediatric and dental sedation caseload were consistent from 2018 to 2019, before dropping by 60% in 2020. The N2O manifold use dropped to 48% of pre-pandemic levels during the same period (Fig. 1) while obstetric caseload together with Entonox consumption remained unchanged. In 2020, dental cases dropped to a minimum allowing us to estimate an average N2O volume use for each case. Subtracting this from the total manifold use, left us with the quantity of N2O used in paediatric theatres. Divided by case numbers, this led to a calculated mean of 150 l N2O per paediatric anaesthetic case. Discussion Although Entonox is self-administered by patients, N2O is provided under the care of an anaesthetist or dentist for analgesia, sedation or anaesthesia. In our hospital, N2O use had a carbon dioxide equivalent footprint of 371 tonnes in 2019 and 208 tonnes in 2020. By establishing a benchmark figure per case, we have a baseline upon which we can measure the effects of any intervention made to decrease N2O usage. We plan to survey current practice amongst paediatric anaesthetists in our hospital, before delivering targeted education sessions and suggestions for reducing N2O usage. This will include reducing flow rates, avoiding N2O altogether where appropriate and consideration of using TIVA. We will prospectively audit N2O consumption to assess the impact of our changes. We hope to provide a leading example of how anaesthetic care of children can be safely adapted to support the NHS's vision of becoming carbon neutral by 2040 [1].