The choice (and switching) of inhaler devices, in particular of DPIs, is a crucial issue in real-life studies since long ago [26]. Systemic reviews on randomized clinical trials did not confirm this evidence because mostly focusing the role of drugs used in the majority of cases. For this reason, patient-centered studies in community setting and/or in unselected samples of subjects had been encouraged in order to provide data much more fitting with real-life conditions and patients behavioral habits [2, 27].
Actually, even if the patients’ opinion has been progressively valued much more than in the past, the assessment of aspects which are highly independent of patients’ personal viewpoint (such as, the device engineering, the training track and the training costs) should further contribute to provide a much more comprehensive and objective picture of the so called “usability” of inhalation devices.
In real life, DPIs are highly prescribed in Italian COPD patients being their prescription usually independent of their known basic characteristics and technical differences, such as the different number of main actions required for their actuation (7 for Breezhaler, 4 for Ellipta and Turbohaler, and 3 for the remaining devices), and their intrinsic resistance, ranging from 0.017 kPa0.5 L/min to 0.039 kPa0.5 L/min [28, 29].
Actually, different DPIs confirmed to provide different performances in terms of patterns of lung deposition and inspiratory flow required for an adequate inhalation. On the other hand, both these factors which mainly attain to the intrinsic engineering of the devices [2, 26, 30], are equally able to affect clinical outcomes, being patients almost completely unaware of their relative value from this point of view [31]. These aspects are recently receiving increasing, even if still insufficient, attention by prescribers. In a multinational survey conducted among primary and secondary care physicians, more than 30% of them considered the device before considering the respiratory drug to prescribe. Moreover, the vast majority of UK health professionals (87%) affirmed to be concerned about possible problems arising from therapeutic prescriptions if the inhalation device is not specified, and 86% of physicians were convinced that DPIs are non-interchangeable and that their unmotivated substitution would have an adverse impact [32].
In several studies (even if mostly consisting of small samples of subjects), the criteria for DPIs preference have been usually related to factors which are strictly dependent of patients’ characteristics, beliefs, and subjectivity, such as: their age, visual acuity, hand strength, coordination, cognition, psychological profile, socio-economic status, and educational level. As a consequence, satisfaction, or intuitivity, or willingness to use, or preference “at glance”, or dexterity, or ease-of-use, or acceptance were from time to time the indices used for assessing and comparing different DPIs [14, 28, 33, 34].
In the last decade, the term “usability” appeared in the literature, but “usability” is ever more frequently used as a synonymous of “ease of use”, even if “usability”, per sé, encases a more complex and multifaceted concept, which depend of several determinants from different domains.
In our opinion, “Usability” should be regarded as a much more comprehensive parameter and its effective value results from the weighted mix of subjective (namely, intuitivity, satisfaction, willingness to use, preference “at glance”, dexterity, ease-of-use, acceptance, etc.) and objective (such as, those independent of patients’ convincement and beliefs, cost included) determinants, all contributing to balance the role of different factors affecting the overall DPIs performance and convenience in real life. To point out that the cost related to DPIs use should also be included among the decision criteria of usability, even if it occurred episodically and usually only related to the cost reimbursement [6, 35].
The existence of different domains affecting DPIs usability is clearly confirmed in the present investigation, which was founded on data collected by means of the multidimensional GUS Questionnaire. To pinpoint that also the patient-dependent criteria of choice (namely, preference and ease-of-use, etc.) were carefully assessed (before instruction) and compared (after instruction) by the expert nurses who provided specific scores in order to check and measure the efficacy of the training track with each DPI.
To emphasize that no DPI achieved the theoretical GUS top score of 50 points, thus confirming that the “ideal DPI” is not still available and that, even if well performing, all presently available DPIs are affected by some critical aspects.
Nevertheless, some relevant differences among the seven DPIs used in the present study clearly came out in terms of their usability and, consequently, of educational actions to deliver for boosting their proper utilization. In particular, Ellipta and Breezhaler proved equally independent of patient’s original level of instruction, even if they were characterized by dramatically different GUS scores (such as, the highest and the lowest, respectively). Actually, this dramatic difference in GUS value may be likely suggested as due to the fact that, differently from all other six DPIs which are multi-dose inhalers, Breezhaler is a single-dose inhaler characterized by a very low intrinsic resistance which requires a very high subject’s inspiratory flow for achieving an effective drug inhalation, and several manoeuvres for its proper actution.
All the other remaining five devices seem to be influenced by a previous DPIs’ experience and their ranking proves very clear according to the GUS score: Turbohaler shows almost 70% of probability to be the 2nd; Diskus has 62% probability to be the 3rd; both Spiromax and Nexthaler have 80% probability to be the 4th, and Genuair has 65% probability to be the 6th.
On the other hand, the corresponding trend assessed in naïve COPD subjects does not result as much clear since Turbohaler, Spiromax, Diskus, and Nexthaler showed a probability of 12–34% to rank as the 2nd up to the 5th most usable device, followed by Genuair ranking 6th or 7th (with a probability of 44 and 35%, respectively), and finally Breezhaler ranking 7th with a probability of 64%. This less defined trend was likely due to the small number of naïve patients evaluated (9 patients in both group 1 and 2, and 11 in group 3) which contributes to increase uncertainty in the analysis; in fact, the 95% CrI presented in Fig. 3-b are larger than those presented in Fig. 3-a.
Moreover, Ellipta, Spiromax, Turbohaler, and Diskus were the DPIs needing the lowest time to spend for achieving the patient’s autonomy and the quickest to learn. Once again, even if the expert nursing of inhalation procedures represents a crucial aspect with all DPIs [8, 29, 36], a careful educational training is mandatory with some DPIs, which are characterized by lower usability scores.
This evidence is further confirming and stressing the original concept that subjects are unable to use all inhalers equally well [1, 2], and that usability consists in and depends of a much more complex set of determinants than simple patients’ perceptions. In particular, each single domain is not able to assess per sé the usability of a DPI, differently from the GUS score, which is able to provide the overall and objective measure of all domains contributing to each DPI usability. Actually, DPIs can be ranked more effectively in terms of their usability when all the components provided by the GUS Questionnaire are weighted together, such as the subjective and objective components of comparison and ranking.
In other words, the GUS score proved able to limit substantially the role of patient-dependent factors of choice, thus leading to a much more reliable assessment of each DPI usability in real life. These results are emphasized by those of the Bayesian model of comparison that confirmed the ranking of the seven different DPIs provided by the GUS score.
The present investigation has some limitations. The present study is a monocentric survey, even if patients participating were from several Italian regions. Geographical distribution was uneven in patients previously experienced in DPIs use: nonetheless, we believe that this does not represent a relevant confounding factor since the national attitude had never been associated to significant regional differences in DPIs’ prescription. Moreover, the original whole sample had to be divided in sub-groups because the GUS Questionnaire consents the comparison of only four devices simultaneously. On the other hand, the simultaneous comparison of more than four DPIs per patient would create severe problems in terms of suitability of their response to the questionnaire. Finally, independently of the strict control of both the quality and duration of the nurses’ explanation of each DPI, it was anyway possible that minimal differences would occur in transferring the messages, even if the high predictivity of GUS score tends to exclude the occurrence of substantial biases from this point of view.
However, a point of strength is that, as the study attains to COPD patients, only the seven mostly used DPIs officially indicated as appropriate for COPD management were considered and compared by means of a strict statistical procedure.