The Importance of Inhaler Technique in Measuring and Calculating Inhaler Adherence, and its Clinical Outcomes
Depending on the population studied, cross-sectional observational studies suggest that between 14%-90% of patients do not use their pressurized metered dose inhaler correctly, while 50-60% misuse a dry powder inhaler. This means that unless incorrect technique is acounted for a significant underestimation of how much medication the person actually obtained may be made.
The aim of this thesis was to objectively determine the frequency and importance of inhaler technique errors and to combine these with inhaler use to provide an acurate method of calculating adherence. I then investigated different patterns of inhaler use, determinants of inhaler use and the impact of education directed at technique of inhaler use has on adherence and clinical outcomes.
To assess inhaler adherence the INhaler Compliance Assessment (INCATM) device was used. This device records digital audio of a patient using their inhaler to provide information on time and technique of use.
Firstly, Inhaler adherence was measured in a cohort of inhaler users recruited from a community care setting. Analysis of the audio recordings showed that these patients made several inhaler errors including generating insufficient inspiratory flow, exhalation into the inhaler mouthpiece after priming, multiple inhalation in one inhaler use, poor breath hold as well as frequntly missing doses. This identified the frequency of inhaler errors. Then I assessed the severity of these errors. Healthy volunteers performed common inhaler errors and drug plasma levels were measured. Results showed that of the errors identified above only poor inspiratory flow, exhalation into the mouthpiece and missed doses affected plasma drug levels. Based on these findings I developed a new method of calculating adherence that incorporated time of use, interval between doses and technique of use. I then prospectively related adherence calculated by this method with clinical outcomes in a cohort of patients with severe asthma. Among over 220 severe asthma patients followed for 3 months, adherence calculated in a way that accounted for time and technique of use, was more reflective of changes in clinical outcomes than current measures of calculating 4 adherence. With this method, I also assessed inhaler adherence in a cohort of Chronic Obstructive Pulmonary Disease patients being discharged from hospital. Adherence was poor in this population, due primarily to poor inhaler technique. Determinants of inhaler adherence were also evaluated leading to the identification of three clusters of inhaler use; those who took their inhaler regularly with good technique, those who took their inhaler regularly with poor technique, and those that took their inhaler irregularly and with poor technique. Finally an education program geared at inhaler technique was implemented in randomised control trial of asthma patients. Inhaler adherence was significantly higher in patients receiving inhaler training based on the individuals own time and technique of use.
These data highlight that both ineffective and irregular inhaler use are common in all users of inhalers and stress the importance of incorporating a measure of inhaler technique when assessing inhaler adherence.