A departmental audit of clinical use of N2O can be helpful on multiple fronts. It allows comparison between procurement and clinical use, with any discrepancies helping identify leaks within the N2O infrastructure. It also allows for understanding of N2O clinical use patterns within the department to help focus interventions to help reduce clinical use of N2O. At SCGH we used both a clinical use survey and anaesthetic machine interrogation to get the required data. We received the procurement data from our local gas provider which in WA is BOC gas. Below are links to our generic survey and machine interrogation information.
Click here to go to machine interrogation information.
Click here to go to generic Clinical Use Survey information.
Nitrous Oxide consumption per episode
| Estimated cylinder requirement and emissions per episode. Based on Australian D cylinder (3520 litres) and Australian C cylinder (935L) allowing for 10% wastage | |||||
| Type of episode | Estimated N2O per episode (L) (Wong et al) | Episodes per C cylinder | Episodes per D cylinder | CO2e (kg) | Equivalent emissions from car travel (km) |
| Paediatric gas induction | 50 | 17 | 64 | 25.5 | 180 km |
| One hour maintenance anaesthesia at 500ml/min @50%FiN2O | 15 | 56 | 213 | 7.65 | 52 km |
| One hour maintenance anaesthesia at 2L/min 50%FiN2O | 60 | 14 | 53 | 30.6 | 208 km |
| Paediatric sedation in ED | 60 | 14 | 53 | 30.6 | 208 km |
| Labour Analgesia | 500 | 1.6 | 6 | 255 | 1740 km |
| Conversion from CO2e to kilometres based on 2021 average petrol passenger car in Australia (146.5 g/km) | |||||
Entonox Cylinders (50% O2, 50% Nitrous Oxide) are available in Australia from BOC with the following sizes useful for point of care.
- C Cylinder – 500 litres
- D Cylinder – 1600 litres
Sources:
Wong A, Gynther A, Li C, Rounds M, Lee JH, Krieser D, et al. Quantitative nitrous oxide usage by different specialties and current patterns of use in a single hospital. Br J Anaesth [Internet]. 2022 Sep 1 [cited 2023 Feb 20];129(3):e59–60. Available from: http://www.bjanaesthesia.org/article/S0007091222002616/fulltext
Back to the future: A return to point-of-care nitrous oxide cylinders (Woinarski C et al, 2025)