Anaesthetic Volatiles, Nitrous and Gas Use in a Tertiary Children's Hospital: A Sustainability Approach

Abstract

The carbon footprint (CO2e) associated with inhalational anaesthesia is disproportionately large, primarily due to the high Global Warming Potential (GWP100) of volatile agents and gases used and their specific chemical composition. (1, 2) The increasing ease of collecting, aggregating, and analysing anaesthetic agent usage data at the whole-of-hospital level presents an opportunity to understand usage patterns, reduce waste, and effectively lower the CO2e of anaesthesia. (3, 4) In this study, we aimed to quantify the usage of sevoflurane, isoflurane, nitrous oxide, oxygen, and medical air for all anaesthetics performed at a large tertiary-quaternary children's hospital in Sydney. To achieve this, we designed and implemented a data capture system, conducting data collection under a Quality Improvement project framework (approval number CHARLI 7197).   By connecting individual anaesthesia workstations from both Draeger and GE manufacturers, featuring various models across the hospital, to a Philips physiological monitoring platform using dedicated devices, we obtained a continuous daily export of all relevant data, polled every 20 seconds, from all anaesthesia machines. This primary data feed was processed and stored in a custom-built PostgreSQL database, enabling us to calculate total gas usage, per-case usage, per-hour usage, and other related metrics across all cases over a 21-month period. In the 21-month period of data collection, there were 22,290 anaesthesia cases. The anaesthesia machines within the MRI rooms could not be linked to the data system adequately and were excluded from this analysis together with cancelled cases and cases with inadequate data, leaving 19,808 cases for the analysis. These results are shown in Table 1. The average fresh gas flow rate during the maintenance of anaesthesia was 2.36l/min, whereas the average fresh gas flow rate in the 10-minute induction period was 5.3l/min.   The sevoflurane usage data obtained from our study aligns well with the hospital-level purchasing data. Notably, apart from anaesthetic bays and operating theatres there is currently no specific mechanism for measuring nitrous oxide usage within the hospital. Instead, we relied on annual purchasing data, which indicated consumption of 2.3 million litres of nitrous oxide during the fiscal year 2019-2020, for the whole of hospital nitrous oxide usage.   When we annualised this purchasing data and compared it with the nitrous oxide usage data from our study, a significant disparity emerged between the anaesthesia-specific nitrous oxide usage and the overall hospital consumption. This discrepancy is partly due to clinical administration in many other hospital areas, including the emergency department (ED), burns service, oncology, or dental sedation. However, the gap between purchased volumes (estimated) and measured anaesthesia use is very large, suggesting that leakage from the 28yr old pipeline infrastructure may play an important role.   The existence of this gap underscores the importance of implementing a more comprehensive measurement mechanism to accurately track and manage nitrous oxide usage across various hospital departments. These results will be useful to improve low-flow anaesthesia practice, quantify and eliminate nitrous oxide leakage, and expand the use of total intravenous anaesthesia.