Carbon footprint and associated costs of asthma exacerbation care among UK adults

Abstract

Introduction

Asthma exacerbations are a primary driver of costs and health impacts from asthma. Despite research suggesting that asthma care has a disproportionate carbon footprint, emissions costs are not considered when evaluating its societal burden. To advance the understanding of greenhouse gas (GHG) emissions associated with asthma, we estimated the carbon footprint and associated costs of asthma exacerbation care by severity level among UK adults.

Methods

Guidelines for asthma exacerbation treatment in UK adults were reviewed by severity level: mild, moderate, and severe/life-threatening. Components of care for each severity were evaluated for GHG emission potential and key drivers were identified. Carbon dioxide equivalent (CO₂e) emissions of drivers were sourced from published literature and combined to estimate the carbon footprint per exacerbation, by severity level. Emissions were scaled up to the annual UK adult population based on the annual number of exacerbations at each severity. Costs associated with emissions were estimated using the UK government’s 2020 nontraded price of carbon, at ₤71 per tonne CO₂e (tCO₂e).

Results

Overall, emissions drivers for exacerbations were medical services, including patient-travel, and quick-relief inhalers. The annual number of mild, moderate, and severe/life-threatening asthma exacerbations among UK adults were 118.9 M, 5.5 M, and 2.4 M. Associated annual carbon footprints were estimated to be 83,455 tCO₂e, 192,709 tCO₂e, and 448,037 tCO₂e for mild, moderate, and severe/life-threatening exacerbations, respectively, with a total of 724,201 tCO₂e. Total annual emissions costs from exacerbation care were £51.3 M; ₤5.9 M, ₤13.6 M, and ₤31.7 M for mild, moderate, and severe/life-threatening exacerbations, respectively.

Conclusion

GHG emissions from asthma exacerbation management were the highest for severe/life-threatening events, followed by moderate exacerbations. Treatment to reduce the severity and occurrence of exacerbations, such as effective, long-term control therapy via lower-emission dry powder inhalers (DPIs), can help mitigate asthma care emissions. For mild exacerbations, the use of DPIs can eliminate associated emissions.

Keywords:

• Asthma exacerbations
• carbon footprint
• climate change
• metered-dose inhalers
• dry powder inhalers

JEL Classification Codes:

• P18
• P1
• P
• O38
• O3
• O
• I18
• I1
• I

Introduction

Asthma is a chronic respiratory disease of the airways and lungs that places substantial burdens on individual patients and on healthcare systems¹. In the UK, for example, the prevalence of asthma is among the highest in Europe, affecting 15.6% of the population, and is associated with approximately one billion pounds of National Health Service (NHS) spending a year². Symptoms include wheezing, chest tightness, and shortness of breath, and may vary in intensity over time¹. In particular, patients may experience episodic acute exacerbations of asthma symptoms that require intensification of usual treatment¹. Asthma exacerbations are associated with worsening of quality-of-life for patients^3,4, are a primary driver of economic burden for health systems and society^5–7, and, in the most severe cases, can be life-threatening¹.

A wide range of effective treatments is available for chronic and acute asthma care, many of which are delivered via device-based, self-administered inhalation. Recently, specific classes of asthma treatments, particularly metered-dose inhalers (MDIs) with hydrofluoroalkane (HFA) propellants, have been identified as important drivers of greenhouse gas (GHG) emissions within the healthcare sector^8–10. Due to the HFAs, MDIs have a disproportionately high carbon footprint, up to 295 times the carbon dioxide equivalent (CO₂e) emissions per therapeutic equivalent compared to substitutable dry power inhalers (DPIs)¹¹. Recognizing the global challenge of climate change, emissions associated with MDIs relative to DPIs have been quantified and integrated into patient-physician shared decision making for asthma care¹² and into health policy¹³ in the UK.

However, the GHG impacts of asthma are likely to extend beyond those associated with inhaler use. Exacerbations in particular, account for the majority of health resource use and costs in asthma care^3,7 and may also be a significant driver of GHG emissions. Indeed, the broad societal costs of asthma exacerbations, including direct costs for urgent care, inpatient stays and quick-relief medications, treatment of sequelae, and indirect costs due to work loss and early mortality, have been central to quantifying the economic burden of asthma and to evaluating the cost-effectiveness of asthma treatments^2,3,7. To quantify the societal impact of asthma more fully, it is important to quantify GHG emissions associated with exacerbations.

To this end, the present study (1) identified key GHG emission drivers amid asthma exacerbation care by severity level, (2) quantified the GHG emissions associated with these drivers, and (3) calculated total GHG emissions and associated costs among UK adults (aged ≥18 years) with asthma by exacerbation severity level.

Methods

Identification of GHG emission drivers

To identify key GHG emission drivers for asthma exacerbation care, a targeted literature search was conducted on websites of UK governmental bodies and key asthma agencies to identify established guidelines for the treatment of asthma exacerbations in UK adult patients. Search terms included a combination of “asthma exacerbations,” “asthma management,” “treatment guidelines,” and “asthma exacerbation severity level.” Guidelines were reviewed by exacerbation severity level, as defined by the American Thoracic Society and European Respiratory Society¹⁴. Exacerbations were classified as mild if they involved symptoms outside the normal range of variation in expiratory flow and medication use for a patient, moderate if they included one of the following: a deterioration in symptoms and/or in lung function, or an increased use of a short-acting beta agonist (SABA); and severe or life-threatening if they required urgent action on the part of the patient and physician to prevent a serious outcome, and manifested in at least one of the following ways: use of systemic corticosteroids, or an increase from a stable maintenance dose for at least 3 days, or a hospitalization or emergency department visit because of asthma, requiring systemic corticosteroids¹⁴.

Once guideline-recommended treatments for each exacerbation severity level were identified, the corresponding components of care were evaluated for GHG emission potential, via consultation with an environmental economist (coauthor TS), to identify key emission drivers. The identified drivers were selected to be nonoverlapping, i.e. additive, drivers of emissions.

Calculation of GHG emissions and associated costs for asthma exacerbation care

A second targeted literature search was conducted on Google Scholar to quantify the CO₂e emissions associated with the identified emission drivers. Search terms included “CO₂e emissions,” “asthma carbon footprint,” “metered-dose inhalers,” “dry powder inhalers,” “exacerbation rates by severity level,” and “social cost of carbon.” To quantify the GHG emissions associated with a single exacerbation episode, by severity level, emissions were summed across all drivers, after multiplying by units of resource use where appropriate. Next, to estimate total CO₂e emissions associated with asthma exacerbation care in UK adults, annual rates of exacerbations among UK adults were extracted from literature, by exacerbation severity level, and then multiplied by the quantified CO₂e emissions per exacerbation. Last, emissions-related costs associated with asthma exacerbation care were calculated using the UK’s 2020 nontraded price of carbon¹⁵, which was inflated from 2018 pounds (£69/tonne of CO₂e [tCO₂e]) to 2020 pounds (£71/tCO₂e) using the UK’s Office for National Statistics consumer price index¹⁶. Sensitivity analyses were conducted by varying the resource utilization and associated emissions for selected drivers within ranges supported by different data sources.

Results

Key emission drivers of asthma exacerbation care

The targeted literature search identified two main documents to inform the identification of key emission drivers of asthma exacerbation care in UK adults: (1) Asthma: diagnosis, monitoring and chronic management from the National Institute for Health and Care Excellence¹⁷, and (2) The British Guideline on the Management of Asthma published by the British Thoracic Society and the NHS¹⁸. These documents provide an overview of the recommended steps in the diagnosis, monitoring, and treatment of asthma in the UK and are targeted to patients with asthma as well as their physicians and caretakers. From a review of these two sources, the following key emission drivers of asthma exacerbation care were identified: (1) the use of short-acting beta-agonist (SABA) bronchodilators for mild, moderate, and severe or life-threatening exacerbations, and (2) medical services provided for the treatment of moderate exacerbations and severe or life-threatening exacerbations, including emissions associated with patient travel to receive these services and the use of any MDIs or anesthetic gases during the visit.

GHG emissions associated with asthma exacerbations by severity

To calculate the GHG emissions associated with SABA bronchodilator use, the carbon footprint associated with a SABA actuation was multiplied by the number of actuations necessary for treatment of an exacerbation, which differed by severity level. Based on the literature, only the use (per actuation) of MDIs was associated with GHG emissions, while the use of DPIs was emission-free⁸. CO₂e per actuation were extracted by inhaler type from Wilkinson et al.⁸ and were evaluated at 120.5 g CO₂e, 49.4 g CO₂e, and 0.0 g CO₂e for large-volume MDIs, small-volume MDIs, and DPIs, respectively. MDI volume referred to the amount of propellant in the device. For each exacerbation severity level, the range of SABA actuations required to treat the exacerbation was extracted from the global initiative for asthma (GINA) 2020 guidelines¹ and Maselli & Peters 2018¹⁹. The midpoint of the range of actuations was used to derive GHG emissions for primary analyses and was 7, 21, and 28 for mild, moderate, and severe or life-threatening exacerbations, respectively.

Exacerbations of greater than mild severity may also require medical services, which can drive further CO₂e emissions beyond those associated with SABA use. Medical services associated with a physician office visit for a moderate exacerbation were associated with an estimated 66 kg CO₂e²⁰. For severe or life-threatening exacerbations, all of which require medical services, average emissions per exacerbation were estimated at 184.7 kg CO₂e. This estimate was calculated as the weighted average of the carbon footprint for acute services by level of care, including emissions due to anesthetic gases and MDIs during the visit, as well as patient travel to the site of care. The carbon footprint of general practice visits, emergency department visits, and hospitalizations were extracted from Tennison et al.²⁰ and were weighted by the exacerbation-related frequency of each, which was estimated from Bloom et al.²¹ For exacerbations requiring hospitalization, the carbon footprint per bed-day was multiplied by the average length of stay, extracted from Jones et al.²²

Based on these components, the total estimated GHG emissions associated with an asthma exacerbation varied based on the exacerbation severity level as well as the type of SABA inhaler used to treat the exacerbation (Table 1). A mild exacerbation was associated with a range of 0.0 kg CO₂e (when a DPI is used) to 0.8 kg CO₂e (when a large-volume MDI is used). While these carbon footprint estimates were minimal in magnitude, large relative differences were found based on the type of SABA inhaler used. The total carbon footprint of a moderate exacerbation differed greatly depending on whether a physician’s office visit was required for treatment or not (Table 1). For moderate exacerbations that did not require medical services, the associated GHG emissions ranged from 0.0 kg CO₂e (with DPI use) to 2.5 kg CO₂e (with large-volume MDI use). On the other hand, moderate exacerbations requiring a physician’s office visit were associated with a carbon footprint ranging from 66.0 kg CO₂e (with DPI use) to 68.5 kg CO₂e (with large-volume MDI use). Severe or life-threatening exacerbations, which always required medical services for treatment, were associated with the greatest carbon footprint, ranging from 184.7 kg CO₂e (with DPI use) emissions to 188.1 kg CO₂e (with large-volume MDI use; Table 1).

Table 1. GHG emissions per asthma exacerbation.

Type of SABA inhaler used	Carbon footprint per exacerbation (kg CO2e)
	Mild exacerbation^a	Moderate exacerbation		Severe or life-threatening exacerbation^b
		Not requiring GP visit^a	Requiring GP visit^b
Large-volume MDI	0.8	2.5	68.5	188.1
Small-volume MDI	0.3	1.0	67.0	186.1
DPI	0.0	0.0	66.0	184.7

Abbreviations. CO₂e, carbon dioxide equivalent emissions; DPI, dry powder inhaler; GHG, greenhouse gas; GP, general practitioner; kg, kilogram(s); MDI, metered dose inhaler, SABA, short-acting beta agonist.

^aThe carbon footprint of a mild exacerbation and of a moderate exacerbation not requiring a GP visit was calculated by multiplying the GHG emissions per actuation by the number of actuations needed for treatment.

^bThe carbon footprint of a moderate exacerbation requiring a GP visit and of a severe or life-threatening exacerbation was calculated by summing the GHG emissions associated with SABA use and the carbon footprint of the medical services required.

Total GHG emissions and associated costs of asthma exacerbation care

Table 2 presents the total annual GHG emissions associated with asthma exacerbation care in UK adults, by exacerbation severity level. Among the UK adult asthma population, there were 118.9 million annual mild exacerbations^23,24, 5.5 million annual moderate exacerbations^3,25, and 2.4 million annual severe or life-threatening exacerbations^1,23. The proportion of exacerbations treated with DPIs and MDIs was assumed to reflect the 2020 market shares of SABAs in the UK. Using IQVIA market data, it was estimated that 4.6% of SABAs were DPIs and 95.4% were MDIs, 21.7% of which were classified as small volume. In the absence of published literature on the proportion of moderate exacerbations requiring a physician office visit, it was assumed that 50% of all moderate exacerbations would require a physician office visit for primary analysis. For mild exacerbations, the annual carbon footprint was estimated at 83,455 tCO₂e. The annual carbon footprint for moderate exacerbations, assuming 50% of them required a physician office visit, was estimated at 192,709 tCO₂e. The annual carbon footprint for severe or life-threatening exacerbations was 448,037 tCO₂e. Using the UK’s 2020 nontraded price of carbon, total costs associated with GHG emissions were estimated at £5.9 million for the care of mild asthma exacerbations, £13.6 million for moderate exacerbations, and £31.7 million for severe or life-threatening exacerbations. Overall, asthma exacerbation care in UK adult patients resulted in a total carbon footprint of 724,201 tCO₂e with an associated cost of £51.3 million per annum.

Table 2. Total annual GHG emissions and associated costs of asthma exacerbation care in UK adults, by exacerbation severity level.

Estimate	Mild exacerbations	Moderate exacerbations	Severe or life-threatening exacerbations
Annual number of asthma exacerbations	118,938,000	5,489,497	2,389,446
Total carbon footprint (tCO2e)	83,455	192,709	448,037
Total carbon footprint costs (GBP)	£5,910,631	£13,648,477	£31,731,935

Abbreviations. GBP, British sterling pound; GHG, greenhouse gas; tCO₂e, tonnes of carbon dioxide equivalent emissions.

Note. The carbon footprint cost was based on the central value of the nontraded price of carbon (UK Department of Business, Energy, & Industrial Strategy).

Sensitivity analyses

One-way sensitivity analyses were conducted to explore potential variations in total GHG emissions for key emissions drivers and associated costs of asthma exacerbation care in UK adults. Input parameters for primary analyses and one-way sensitivity analyses are presented in Table 3. The first sensitivity analysis involved varying the number of actuations required to treat an exacerbation, using the upper and lower bounds of actuations reported in the GINA 2020 guidelines and other peer-reviewed literature^1,19. The range of actuations varied between 4–10, 12–30, and 16–40, for the treatment of a mild, moderate, and severe or life-threatening exacerbation, respectively. The proportion of small vs. large volume MDIs used for treatment of exacerbations was varied based on assumptions made about MDIs not classified by volume. From the UK IQVIA market share data, three categories of SABA MDIs were identified: Ventolin (a large-volume MDI)²⁶, Salamol (a small-volume MDI)²⁶, and others (e.g. Salbutamol LU, Terbutaline, Bricanyl) which could not be classified based on available literature. In the sensitivity analysis, the lower bound assumed unclassified SABA MDIs were small-volume while the upper bound assumed they were large-volume. A third sensitivity was conducted to estimate the impact of replacing all MDI SABA use for exacerbations with DPI SABA use. Due to the absence of data regarding the proportion of moderate exacerbations requiring a physician office visit, we conducted a sensitivity analysis that varied the proportion used in the primary analysis by 20% in either direction. This resulted in a lower bound of 30% and an upper bound of 70%. Last, the effects of variations in the value of the nontraded price of carbon were explored using the range (£35–£104) offered by the UK’s Department of Business, Energy, & Industrial Strategy¹⁵, inflated to 2020 pounds (£36–£107).

Table 3. Parameter inputs for the primary and sensitivity analyses.

Parameter	Mild exacerbations	Moderate exacerbations	Severe or life-threatening exacerbations
Number of actuations required to treat an exacerbation^a
Primary analysis	7	21	28
Sensitivity lower bound	4	12	16
Sensitivity upper bound	10	30	40
Proportion of small volume MDIs^b
Primary analysis	21.7%	21.7%	21.7%
Sensitivity lower bound	18.5%	18.5%	18.5%
Sensitivity upper bound	33.1%	33.1%	33.1%
Proportion of DPI SABAs used to treat exacerbations
Primary analysis	4.6%	4.6%	4.6%
Sensitivity lower bound	–	–	–
Sensitivity upper bound	100%	100%	100%
Proportion of moderate exacerbations requiring a physician’s office visit
Primary analysis	–	50%	–
Sensitivity lower bound	–	30%	–
Sensitivity upper bound	–	70%	–
Nontraded price of carbon^c
Primary analysis	₤71	₤71	₤71
Sensitivity lower bound	₤36	₤36	₤36
Sensitivity upper bound	₤107	₤107	₤107

Abbreviations. DPI, dry powder inhaler; MDI, metered dose inhaler; SABA, short-acting beta agonist.

^aThe number of actuations required to treat an exacerbation was varied based on the range of actuations provided by treatment guidelines (Maselli 2018 and GINA 2020).

^bThe distribution of small vs. large volume MDIs was varied based on assumptions made about SABA MDIs not classified by volume. The lower bound assumed unclassified SABA MDIs were small-volume while the upper bound assumed they were large-volume.

^cThe carbon footprint cost was based on the lower and upper bound of the range of the nontraded price of carbon (UK Department of Business, Energy, & Industrial Strategy).

Table 4 presents the corresponding GHG emissions estimated per asthma exacerbation. If an MDI was used to treat a mild exacerbation, varying the number of actuations to the lower bound limit decreased the carbon footprint by 67% whereas using the upper bound limit of actuations increased the carbon footprint by 167%. Despite these variations, emissions remained minimal in absolute terms. For moderate and severe or life-threatening exacerbations treated with an MDI, varying the number of actuations had minimal effects on the overall carbon footprint, as the medical services provided for treatment were responsible for the vast majority of associated CO₂e emissions. Varying the number of actuations was found to have no effect on the carbon footprint of an asthma exacerbation when a DPI was used for treatment. Table 5 presents the total GHG emissions and associated costs for the adult UK population for the rest of the sensitivity analyses. It was found that varying the number of actuations needed to treat mild exacerbations to the lower and upper bounds of the suggested range resulted in a 43% change in total emissions in either direction. However, for moderate and severe or life-threatening exacerbations, the resultant change was 3% and 1%, respectively. Varying the distribution of small-volume vs. large-volume MDIs based on IQVIA market share data resulted in an 8% decrease in GHG emissions and associated costs due to mild exacerbations care when the unclassified MDIs were assumed to be small-volume, and a 2% increase in GHG emissions and costs when they were assumed to be large-volume. For the treatment of moderate and severe or life-threatening exacerbations, varying the distribution of small-volume vs. large-volume MDIs had a negligible effect on total GHG emissions and costs.

Table 4. GHG emissions per asthma exacerbation—sensitivity analysis.

Type of SABA inhaler used	Carbon footprint per exacerbation (kgCO2e)
	Mild exacerbation	Moderate exacerbation		Severe or life-threatening exacerbation
		Not requiring GP visit	Requiring GP visit
One-way sensitivity: Varying the number of actuations required to treat an exacerbation^a
Large-volume MDI	0.5 − 1.2	1.4 − 3.6	67.4 − 69.6	186.6 − 189.5
Small-volume MDI	0.2 − 0.5	0.6 − 1.5	66.6 − 67.5	185.5 − 186.7
DPI	0.0 − 0.0	0.0 − 0.0	66.0 − 66.0	184.7 − 184.7

Abbreviations. DPI, dry powder inhaler; GHG, greenhouse gas; GP, general practitioner; kgCO₂e, kilograms carbon dioxide equivalent emissions; MDI, metered dose inhaler; SABA: short-acting beta agonist.

^aThe number of actuations required to treat an exacerbation was varied based on the range of actuations provided by treatment guidelines (Maselli 2018 and GINA 2020). For mild exacerbations, the range was 4–10 actuations, for moderate exacerbations it was 12–30 actuations, and for severe or life-threatening exacerbations it was 16–40 actuations.

Table 5. Total annual GHG emissions and associated costs of asthma exacerbation care—sensitivity analysis.

Estimate	Mild exacerbations	Moderate exacerbations	Severe or life-threatening exacerbations
One-way sensitivity: Varying the number of actuations needed to treat an exacerbation^a
Total carbon footprint (tCO2e)	47,688 − 119,221	187,756 − 197,661	445,163 − 450,911
Total carbon footprint costs (GBP)	£3,377,503–£8,443,758	£13,297,733–£13,999,221	£31,528,375–£31,935,496
One-way sensitivity: Varying the distribution of small vs. large volume MDIs^b
Total carbon footprint (tCO2e)	77,017 − 85,262	191,817 − 192,959	447,520 − 448,182
Total carbon footprint costs (GBP)	£5,454,673–£6,038,619	£13,585,344–£13,666,198	£31,695,295–£31,742,220
One-way sensitivity: Assuming 100% of SABAs used to treat exacerbations are DPIs
Total carbon footprint (tCO2e)	0	181,153	441,331
Total carbon footprint costs (GBP)	£0	£12,830,074	£31,256,961
One-way sensitivity: Varying the proportion of moderate exacerbations requiring a physician’s office visit^c
Total carbon footprint (tCO2e)	83,455	120,247 − 265,170	448,037
Total carbon footprint costs (GBP)	£5,910,631	£8,516,447–£18,780,507	£31,731,935
One-way sensitivity: Varying the nontraded price of carbon^d
Total carbon footprint (tCO2e)	83,455	192,709	448,037
Total carbon footprint costs (GBP)	£2,998,146–£8,908,777	£6,923,140–£20,571,617	£16,095,909–£47,827,844

Abbreviations. DPI: dry powder inhaler; GBP: British sterling pound; GHG: greenhouse gas; MDI: metered dose inhaler, SABA: short-acting beta-agonist; tCO₂e: tonnes of carbon dioxide equivalent emissions.

^aThe number of actuations required to treat an exacerbation was varied based on the range of actuations provided by treatment guidelines (Maselli 2018 and GINA 2020).

^bThe distribution of small vs. large volume MDIs was varied based on assumptions made about SABA MDIs not classified by volume. The lower bound assumed unclassified SABA MDIs were small-volume (total 33.1% of small-volume MDIs), while the upper bound assumed they were large-volume (total 18.5% small-volume MDIs).

^cThe proportion of moderate exacerbations requiring a physician’s office visit was varied ±20% of the proportion used in the main analysis (i.e. 50%).

^dThe carbon footprint cost was based on the lower and upper bound of the range of the nontraded price of carbon (UK Department of Business, Energy, & Industrial Strategy).

The impact of replacing all MDI SABA use for exacerbations with DPI SABA use varied across exacerbation severity level. For mild exacerbations, this dropped GHG emissions and associated costs to zero, while for moderate and severe or life-threatening exacerbations, both emissions and associated costs exhibited modest reductions (6% and 1%, respectively). Varying the proportion of moderate exacerbations requiring a physician office visit from 50% to 30% or 70% resulted in a 38% change in total GHG emissions and associated costs. Last, varying the value of the nontraded price of carbon resulted in a 49% decrease in carbon costs (lower bound) or a 51% increase in carbon costs (upper bound) for all exacerbation severity levels (Table 5).

Discussion

This is the first study to quantify GHG emissions and associated costs for asthma exacerbations among UK adults. The total annual carbon footprint of asthma exacerbation care in UK adults was estimated to be 724,201 tCO₂e, which is equivalent to GHG emissions from approximately 157,000 passenger vehicles driven in a year and is associated with a carbon cost of £51.3 M.

We found that despite representing only 2% of total asthma exacerbations in UK adults, severe or life-threatening exacerbations produced a carbon footprint greater than that of mild and moderate exacerbations combined, which underscores the societal burden of severe or life-threatening asthma exacerbations. Moreover, the sensitivity of GHG emissions associated with moderate exacerbation care to variations in the proportion of exacerbations requiring physician office visits indicates that exacerbations requiring encounters with the healthcare system drive the carbon footprint of asthma exacerbations in the UK adult population. As the severity of an exacerbation is highly associated with poorly controlled asthma¹, efforts to mitigate the clinical burden of moderate and severe or life-threatening exacerbations by encouraging the appropriate use of long-term control therapy will also mitigate the environmental burden by reducing the frequency and severity of associated healthcare encounters.

Our primary analyses show that unlike moderate and severe or life-threatening exacerbations, the carbon footprint of a mild exacerbation largely depends on the type of SABA inhaler used to treat the exacerbation. Our results extend findings from literature which indicate that the type of inhaler used to treat asthma has a noticeable impact on the amount of CO₂e emissions associated^8,9. The market data used in this analysis show that MDIs make up approximately 95% of all SABA inhalers in the UK. Sensitivity analyses conducted in this study suggest that if all SABAs used for treatment of mild exacerbations in the UK were switched to DPIs, there would be a 100% reduction in GHG emissions, translating to a £5.9 M reduction in carbon costs. As the technology required to eliminate all propellant use in inhaler devices now exists in the form of DPIs¹¹, healthcare authorities and clinicians in the UK can influence patient choice by prioritizing DPIs for the treatment of mild asthma exacerbations, and thereby reduce GHG emissions associated with care.

The external cost associated with the carbon footprint of asthma exacerbation care was estimated to be around £51.3 M annually, of which £5.9 M was due to mild exacerbation care, £13.6 M was due to moderate exacerbation care, and £31.7 M was due to severe or life-threatening exacerbation care. To our knowledge, our analysis is the first to assign a monetary value to the climate impacts of asthma exacerbations. By doing so, we highlight that climate considerations can potentially be incorporated in cost analyses associated with asthma care and treatment. If these emissions costs are taken into consideration, the true cost of asthma exacerbations from the societal perspective may be higher than estimated by typical burden estimates. Similarly, the value of preventative treatments that avert asthma exacerbations would be greater if the climate implications of the exacerbations and the intervention itself are considered. As methods for incorporating climate impacts in health technology assessments are developed and validated in the future, consideration of the climate impacts of asthma exacerbations may also facilitate a more comprehensive evaluation of asthma therapies.

Several limitations should be considered when interpreting the results of this analysis. As this analysis only focused on the key emission drivers identified from a targeted literature search and did not include secondary drivers, estimated CO₂e emissions may be an underestimate of the true carbon footprint of asthma exacerbation care in UK adults. Likewise, this analysis quantified the number of SABA actuations associated with a peak exacerbation event from literature and may underestimate the true number of actuations needed to treat all exacerbations (peak and nonpeak), thereby underestimating the carbon footprint of asthma exacerbation care. Last, due to the lack of data on mild and moderate asthma exacerbation rates among children and adolescents, this analysis focused on UK adults and did not consider exacerbation care in the UK pediatric population. As such, the total GHG emissions and costs associated with asthma exacerbation care in the entire UK population could not be fully estimated. This represents an important limitation. According to NHS England, asthma is the most common chronic condition among UK children, with around one million children receiving treatment for asthma²⁷. Additionally, the UK reports the highest prevalence and emergency admission rates for childhood asthma across Europe²⁷. As a result, asthma exacerbation care among the pediatric population poses a substantial burden on the UK health system²⁸. Thus, asthma exacerbation care in children may also be a significant driver of GHG emissions. Indeed, MDIs which have a higher carbon footprint than DPIs are the preferred SABA delivery method suggested by BTS guidelines for pediatric patients¹⁸. This is due to differences in patients’ ability to successfully self-administer the aerosol, especially for children under 5 years of age²⁹. Given the high prevalence of asthma and associated inhaler use among children, further research to estimate asthma exacerbation rates among the pediatric population is needed in order to provide a comprehensive assessment of the carbon footprint and associated costs of asthma care in the UK.

There are several strengths to our study. First, in the absence of primary data sources, our analysis relied on a combination of recent information from peer-reviewed literature and guidelines from government agencies to estimate the carbon footprint of asthma exacerbation care in UK adults and highlights the environmental impact of inadequately managed asthma. Second, data related to exacerbation rates, exacerbation care, and carbon pricing were specific to the UK, making it particularly useful and applicable to UK health technology assessments. Finally, our analysis may encourage researchers in other therapeutic areas that also make substantial use of HFAs, such as anesthesia²⁶, to quantify the carbon footprint of standard care and consider the value of lower carbon footprint alternatives.

There has been increasing awareness in the UK about the climate impacts of the healthcare sector, and a consequent rise in interest to mitigate them. The healthcare sector is estimated to emit around 5.4% of the UK’s total carbon footprint, with acute care services contributing disproportionately to this fraction³⁰. Appropriately, the UK’s Climate Change Act of 2008, which aims to reduce 2050 net carbon footprint in the UK to at least 1990 levels, includes the healthcare sector as a potential target³¹. The NHS has since mandated sustainable development and resource use reduction in health and social care, which has resulted in a 19% reduction in the associated carbon footprint from 2007 to 2019, despite a 27% increase in activity³². More recently, the UK’s Royal Pharmaceutical Society has committed to taking action in face of the climate and ecological crisis³³. In this context, our analysis sheds light on components of asthma exacerbation care that contribute to the UK healthcare sector’s carbon footprint. Efforts to reduce carbon emissions from asthma exacerbations can be directed at identified emissions drivers, helping advance the NHS’ goal of reducing the healthcare sector’s contributions to the UK’s total carbon footprint.

Conclusions

Findings from this analysis elucidate the carbon footprint and associated costs of asthma exacerbations in UK adults, which are driven by medical services provision for moderate and severe exacerbations and the use of SABA MDIs for mild exacerbations. As healthcare decision-makers in the UK become more vigilant about reducing the healthcare sector’s carbon footprint, the identified GHG emissions from asthma exacerbation care are a potential source that can be targeted. To do so, healthcare decision-makers can focus on providing effective long-term control therapy to reduce the frequency and severity of exacerbations, in lower-emission dry powder inhalers, and encouraging the use of lower-emission (DPI) SABAs for exacerbation treatment.

Transparency

Declaration of funding

This study was funded by Novartis Pharma AG, whose employees were involved in the study design, writing of the report, and the decision to submit the paper for publication.

Declaration of financial/other relationships

IF, JS, KKS, KN, and TS are employees of Analysis Group, Inc. a consultancy that received funding from Novartis Pharma AG to conduct this study. PT is the director of PT Health Economics Ltd, a consultancy that received funding from Novartis Pharma AG to consult on this study. JM and RI are employees of and own stocks in Novartis Pharma AG. JM has received medical writing services from Novartis Pharma AG. AC and HK are employees of Novartis Healthcare Private Limited.

A reviewer on this manuscript has disclosed that they have performed consulting, served on advisory boards, or received travel reimbursement from Amphastar, AstraZeneca, Chiesi, Connect Biopharma, GlaxoSmithKline, Mylan, Novartis, Sunovion, and Theravance. They have also conducted multicenter clinical research trials for some 40 pharmaceutical companies. The other peer reviewers on this manuscript have no other relevant financial relationships or otherwise to disclose.

Author contributions

All authors contributed to the study design and conception. IF, KKS, and KN conducted the analyses. IF, JS, KKS, KN, and TS drafted the initial manuscript. All authors revised the manuscript. All authors approved the final manuscript as submitted.

Previous presentation

These data were previously presented at the ISPOR EUROPE 2021 Annual Congress.

Acknowledgements

None reported.