Assessing fullness of asthma patients' aerosol inhalers

The importance of regular medication in order to control asthma symptoms is recognized. However, there is no accurate mechanism for assessing the fullness of aerosol inhalers. The contribution to asthma morbidity of unexpectedly running out of inhaled medication is unknown.

A study was undertaken to determine how patients assess inhaler fullness and the accuracy of their assessments, and to evaluate the floatation method of assessing inhaler fullness.

An interview survey of 98 patients (51% of those invited to take part), using 289 inhalers, was completed at one general practice in Hampshire.

One third of participants said they had difficulty assessing aerosol inhaler fullness and those aged 60 years and over were found to be more inaccurate in assessing fullness than younger participants. Shaking the inhaler to feel the contents move was the commonest method of assessment. When placed in water, an inhaler canister floating on its side with a corner of the canister valve exposed to air indicates that the canister is less than 15% full (sensitivity 90%, specificity 99%).

Floating a canister in water provides an objective measurement of aerosol inhaler fullness. Providing the method is recommended by the aerosol inhaler manufacturer, general practitioners should demonstrate the floatation method to patients experiencing difficulty in assessing inhaler fullness.