A weighing method for measuring nitrous oxide leakage from hospital manifold-pipeline networks.

Nitrous oxide is a potent greenhouse gas and ozone-depleting agent with a long atmospheric lifetime. Several previous reports indicate that over half of supplied nitrous oxide is wasted from leaking manifold-pipeline systems infrastructure prior to patient use, and that remediating leaks can have significant environmental benefits. We describe an accurate, simple and cost-effective cylinder weighing method to quantify nitrous oxide leak from the manifold-pipeline network at our tertiary non-obstetric facility. Nitrous oxide cylinder depletion was prospectively compared with clinical usage derived from the electronic medical record over an 18-day period. A total of 1932 l (3.62 kg) of nitrous oxide was used in 35 operating theatre cases during the period. This was only 16.5% of actual cylinder depletion (11,686 l; 21.88 kg), indicating that 83.5% (9754 l; 18.26 kg) of nitrous oxide had leaked to the atmosphere (376 ml/minute; 22.6 l/hour; 542 l/day). The fraction of nitrous oxide wasted was consistent with a retrospective analysis of the previous 2-year period at the site that compared purchasing records with estimated clinical use. If maintained over a year, the leak would be equivalent to 101 tonnes of carbon dioxide per annum.