The effect of mode of inhaled salbutamol delivery on measures of small airways obstruction in asthma: a comparison of treatment delivered via spacer and nebuliser

Background Conventional clinical respiratory tests tell us little about the small airways of the lung (less than 2 mm in internal diameter). Patients with asthma affecting the small airways may respond differently to inhaled bronchodilator treatment (salbutamol) depending on the method of administration. Aims In this study, we aimed to assess if there was a difference in the effect of salbutamol treatment via metered-dose inhaler (MDI) and spacer compared to via nebuliser on measures of small airways function. It was hypothesised that the nebulised salbutamol would have a greater effect on the outcome measures due to the particle size being more appropriate for penetrating the smaller airways. Methods Two visits were completed by 14 participants with stable asthma. At both visits, lung function tests were completed both before and after administration of 1 mg salbutamol to measure airway obstruction (spirometry), mechanical load to ventilation (impulse oscillometry), and ventilation heterogeneity (multiple breath nitrogen washout). At visit one, seven participants were randomized to take salbutamol via MDI and spacer, and seven via nebuliser. At visit two, all participants took salbutamol via whichever method they had not been given at visit one. Results Results indicated that participants given salbutamol via MDI and spacer (compared to via nebuliser) showed a greater improvement, which was statistically significant, between the pre- and post-salbutamol values for most lung function tests. Discussion This result was unexpected and may have been due to greater wastage of drug via nebuliser than via MDI and spacer, and differing inhalation patterns. Tidal breathing during nebulised administration, and deep inhalation during use of MDI and spacer, could have affected the delivery of the drug. Conclusion This study implies that taking salbutamol via MDI and spacer would be beneficial if higher doses (e.g. 1 mg) were taken.