Use of metered dose inhalers for bronchodilator responsiveness testing: laboratory practices in Australia and opportunities for carbon footprint reduction.

Background: Metered dose inhalers (MDIs) are important devices for delivering inhaled medications; however, they have an outsized carbon footprint due to their propellant gas. Many short-acting beta-agonist inhalers contain HFA-134a which has a global warming potential >1000 fold higher than carbon dioxide. We aimed to determine the practices around MDI use and disposal within Australia's major lung function testing laboratories and identify the actions that most influence the carbon footprint of bronchodilator responsiveness (BDR) testing.

Methods: Australia's 45 accredited lung function laboratories were invited to participate in an online survey asking about their volume of BDR testing, as well as practices around MDI use such as the number of actuations per BDR test, reuse of MDIs between patients and disposal method. We calculated MDI-associated carbon dioxide equivalent (CO2e) emissions by combining previously published estimates.

Results: 39 laboratories completed the survey. Most laboratories used 4 actuations of salbutamol per BDR test for both adults (27/34, 79.4%) and children (17/20, 85%), but this ranged from 2 to 12. Only three (7.7%) laboratories did not routinely reuse MDIs between patients; however, they all sent their used MDIs for high-temperature incineration. Based on different combinations of observed MDI practices in Australia, we identified a potential sixfold difference in CO2e per 100 BDR tests, from as low as 23.3 kg CO2e up to 166 kg CO2e.

Conclusions: We identified three key practices to reduce the carbon footprint of BDR testing: disposing of MDIs via high-temperature incineration, reducing the number of actuations per BDR test and reusing MDIs between patients.