Estimate of the total carbon footprint and component carbon sources of different modes of labour analgesia

Abstract

The UK National Health Service’s Sustainable Development Unit calculated that 30% of greenhouse gas emissions from anaesthetic services in 2017 were attributable to nitrous oxide used in maternity services [1]. We set out to compare the carbon dioxide equivalence (CO2e) of pharmaceutical options for labour analgesia to help inform UK healthcare staff and patients. A 4-h time period was used to compare the ‘scope 1’ greenhouse gas emissions (‘scope 1’ being direct emissions from owned or controlled sources [2]) associated with different forms of labour analgesia (see Table 1). Established emission factors and lifecycle assessments were used to calculate the CO2e related to drug manufacture; unmetabolised gas emissions; oxygen; disposables; packaging; waste management; and electricity to power administration pumps. Entonox™ (50:50 nitrous oxide/oxygen) calculations were based on a global warming potential over 100 years (GWP100) of 265 [3] for a 70 kg parturient (minute ventilation 14 l.min-1 during labour) inhaling Entonox intermittently for 1 min per contraction, with a contraction rate of 3 in 10 min. The energy required for a litre of oxygen supplied from liquid oxygen was taken to be 0.001 kWh [4]. Energy required to power the epidural and patient-controlled analgesia (PCA) pumps was taken from the manufacturer's power ratings and 0.212 kgCO2e.kWh-1 for electricity generation [2]. We assumed that all single-use components were disposed of in the clinical wastestream by high-temperature incineration (1.074 kgCO2e per kg) and that packaging was treated as domestic waste and processed by low-temperature incineration (0.172 kgCO2e per kg) [5]. Entonox (50:50 N2O/O2) Epidural 0.1% bupivacaine with 2 μg.ml-1 fentanyl 20 ml loading dose 40 ml.h-1 (140 ml over 4 h) Intermittent inhalation of Entonox (18 min.h-1) is associated with the highest carbon emissions at 237.33 kgCO2e, equivalent to driving over 1400 km in an average car. Epidural analgesia and remifentanil PCA have comparable environmental impacts for a 4-h period: 1.2 kCO2e (7 km driving distance) and 0.75 kgCO2e (4 km driving distance), respectively. Intramuscular morphine has the lowest CO2e: 0.08 kgCO2e (0.45 km driving distance) for two 10 mg doses (Fig. 1). Epidural and remifentanil PCA provide superior analgesia at a fraction of the CO2e, but are not available in all birth settings. For epidural analgesia, the disposables required for insertion are responsible for over 70% of emissions, the largest single contributor being the single-use sterile gown. Changing to reusable gowns and drapes and streamlining packs to limit waste would reduce the carbon impact of epidural analgesia. Remifentanil PCA has a favourable CO2e, but is not routinely used in the majority of delivery suites due to the additional monitoring required. As the hourly greenhouse gas impact of remifentanil includes ongoing oxygen delivery, epidurals have a favourable carbon effect over a longer period. There is an alternative inhaled analgesic that could be considered. Methoxyflurane is a volatile agent with a favourable GWP100 (4 compared with 265 for nitrous oxide [3, 6]) used for managing acute pain. The maximum 24-h dose is two methoxyflurane inhalers, the carbon footprint of which is 0.834 kgCO2e. This would only last up to 2 h, limiting its utility for labour analgesia. It could be beneficial for short procedures such as instrumental delivery, perineal repair or as bridging analgesia during epidural placement, but is not currently licensed for use in pregnancy. Nitrous oxide is inexpensive, safe and easy to administer, and National Institute for Health and Care Excellence guidance recommends that it should be available in all birth settings [7], despite a lack of clear quantitative evidence of its analgesic efficacy for labour. As every minute of use contributes over 3 kgCO2e, shortening the duration of use can reduce its environmental impact. Potential leakage of Entonox from pipelines and Schrader outlets would further add to its greenhouse gas impact. Pregnant women should be provided with information about the effectiveness and risks associated with different forms of labour analgesia, including their environmental impact. Involving midwifery and medical staff in educational programmes may help reinforce the environmental message and encourage an informed choice. If a parturient chooses epidural or opioid analgesia, then avoiding delays in administration could reduce consumption of nitrous oxide. Introduction of nitrous oxide capture and catalytic destruction devices in Swedish hospitals and maternity units resulted in a 50% reduction in greenhouse gas emissions [8]. Catalytic destruction devices can be mobile or central units; both require specialised delivery systems and the latter also necessitates central scavenging. Acquiring and installing catalytic destruction units would require significant investment but has the additional benefit of reducing environmental exposure to nitrous oxide for patients and staff. Mobile nitrous oxide destruction units are currently being tested in several UK hospitals. Judicious use of Entonox, reducing waste in delivery systems and utilising catalytic destruction systems could have a huge impact on reducing greenhouse gas emissions from maternity services. This multifaceted approach, along with considering ways to reduce greenhouse gas emissions associated with other forms of labour analgesia such as reducing waste; recycling; and using renewable energy sources, is essential to help the NHS become net zero by 2050. The authors thank F McGain, Western Health, Melbourne and S McAlister, University of Melbourne for their advice and support with this work. TP has chaired a webinar hosted by Fisher Paykel, for which he received an honorarium, and delivered a lecture to the Liverpool Society of Anaesthesia for which he received an honorarium. No other competing interests declared.

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