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

Background: Nitrous oxide (NO) is a potent greenhouse gas that contributes significantly to the healthcare sector's carbon footprint. Pre-utilisation losses of NO are up to 95%. Decommissioning manifolds can reduce these losses.

Methods: Hospitals in our Greater London research network with at least one active NO manifold were included in the Nitrous Oxide Manifold and Other Reduction of Emissions (NoMoreGas) study. NO 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 NO and the quantity procured by hospitals, referred to as the 'NO gap'. Secondary outcomes included anaesthetists' self-reported utilisation of NO and their opinions on manifold decommissioning.

Results: Eighteen of 53 hospitals were included. In total, 6 487 200 L of NO 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 NO. 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 NO procured, suggesting pre-utilisation losses of 5 311 852 L. Among surveyed anaesthetists, 70% (n=309) reported using NO 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 NO procured and utilised clinically, indicative of significant pre-utilisation losses. Our findings support the decommissioning of NO manifolds for environmental and economic benefits.