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

Figures & data

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.

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).

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. 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).