Nitrous oxide is a known greenhouse gas, with a global warming potential 274 times greater than carbon dioxide and an extended atmospheric lifetime of more than 100 years. The gas is used clinically as a common adjunct to analgesia in labour, for sedation in procedures such as dentistry, and as a part of general anaesthesia. Anaesthetic gases make up 2-5% of a tertiary hospital’s carbon footprint, with most of these emissions attributed to nitrous oxide.
In NSW public hospitals, nitrous oxide is supplied commercially in cylinders of varying sizes. These cylinders provide gas either directly at the point of patient care, or through a central manifold system—a gas distribution system that connects multiple gas lines into a single channel—which is accessed via wall outlets. Published research on manifold systems shows that pipeline leaks are common and have negative environmental and financial impacts. Associated occupational health risks are also well documented.
Assessing clinical uses and infrastructure
The nitrous oxide project at St George Hospital in South Eastern Sydney Local Health District (SESLHD) aimed to assess the hospital’s nitrous oxide clinical use pattern and infrastructure integrity. Clinical use was assessed through a survey of the anaesthetic department and an audit of maternity use documented in eMaternity. Infrastructure integrity was assessed by a four-hour whole of manifold system pressure test. The first of its kind at SESLHD, the project aimed to undertake the following assessments.
- Assessment of procurement data and calculation of the associated carbon footprint (2021 as the baseline year).
- Assessment of nitrous oxide use by specialty (anaesthesia, obstetrics, and ED).
- Assessment of pipeline leaks by pressure testing.
A clinician survey was developed to estimate nitrous oxide use for anaesthetic practices. Obstetric use during the procurement period (calendar year 2021) was evaluated using summary data from eMaternity records, which were then cross referenced with eMR labour documentation to ensure all episodes of obstetric use were captured.
Discussions were held with other specialty representatives (emergency medicine and paediatrics) to estimate nitrous oxide use outside theatres and delivery suite (primarily procedural analgesia/sedation). Outcome measures included the carbon footprint of procured nitrous oxide, an estimate of clinical use and leak identification.
Leaks found in several operating theatres
The project was successful in assessing nitrous oxide use, infrastructure and staff attitudes regarding nitrous oxide use. In 2021, St George Hospital purchased 2,235kg of nitrous oxide, generating a carbon footprint of 592 tonnes CO2e. The carbon footprint is greater than that generated by clinical use alone secondary to leaks identified in the pipeline infrastructure.
Use in obstetrics was slightly higher than published estimates (likely due to cross checking summary data with labour and delivery documentation). The project team found that use in anaesthesia is declining and predominantly associated with paediatrics. Infrastructure pressure testing found leaks in several operating theatres which will be addressed to relieve environmental and occupational health risks.
The project team experienced challenges in coordinating the technical services needed to assess and find pipeline leaks, due to significant workforce shortages. However, the team confirmed a clinical use pattern similar to other principal teaching hospitals, with infrequent use of nitrous oxide as an adjunct to general anaesthesia.
Future studies looking to undertake a similar project require engagement of a licensed medical gas technician to oversee pipeline testing. There is limited published research on issues related to nitrous oxide supply and infrastructure leaks in obstetrics and maternity. This is an area for improved education and collaboration.
