Nitrous Oxide Manifold and Other Reduction of Emissions (NoMoreGas): a multicentre observational study evaluating pre-utilisation loss of nitrous oxide.

Background: Nitrous oxide (N₂O) is a potent greenhouse gas that contributes significantly to the healthcare sector's carbon footprint. Pre-utilisation losses of N₂O are up to 95%. Decommissioning manifolds can reduce these losses.

Methods: Hospitals in our Greater London research network with at least one active N₂O manifold were included in the Nitrous Oxide Manifold and Other Reduction of Emissions (NoMoreGas) study. N₂O utilisation data were collected continuously over 5 days and extrapolated over a year, in addition to collecting procurement records from the preceding financial year. The primary outcome was the discrepancy between clinically utilised N₂O and the quantity procured by hospitals, referred to as the 'N₂O gap'. Secondary outcomes included anaesthetists' self-reported utilisation of N₂O and their opinions on manifold decommissioning.

Results: Eighteen of 53 hospitals were included. In total, 6 487 200 L of N₂O were procured with a median (IQR) of 304 200 (183 600-473 400) L per site. During the 5-day data collection period, sites utilised a median (IQR) of 501 (42-1409) L of N₂O. Extrapolating over a year resulted in a median (IQR) annual utilisation of 36 573 (3066-102 857) L per site and a total of 1 175 348 L. This represented an estimated 18% of the N₂O procured, suggesting pre-utilisation losses of 5 311 852 L. Among surveyed anaesthetists, 70% (n=309) reported using N₂O within the previous year, with one-third (n=97) using it once a week or more. There was widespread support for decommissioning manifolds.

Conclusions: Consistent with other reports, the data demonstrate a substantial discrepancy between the quantities of N₂O procured and utilised clinically, indicative of significant pre-utilisation losses. Our findings support the decommissioning of N₂O manifolds for environmental and economic benefits.