A vast number of inhalation devices exist and each device has specific requirements to achieve optimum inhalation of the drug. Currently, there is no overview of inhalation requirements considering all devices. This article presents a review of the literature on different inhalation device requirements and incorporates the data into a new inhalation flow algorithm.

Quite often, inhalers are considered easy to use and patients do not receive adequate training even though it has been estimated that up to 68% of patients do not use their inhalers correctly.

A number of devices available with medications in powder form. The quality of inhalation devices is generally high and active drug delivery is reliable if the devices are used properly. The key factors for successful inhalation, however, involve the right particle size and a proper respiratory manoeuvre on the part of the patient.

Data from literature on commercially available inhalation devices were evaluated and parameters, such as inhalation flow rate, flow acceleration, inhalation volume, and inspiration time assessed for the required inhalation manoeuver specific to the device. All agreed upon data points were used to develop an inhalation flow algorithm. A review of the literature revealed distinct differences between inhalation devices regarding the optimum inhalation manoeuver.


Considering the multitude of different inhalation devices, patients should be aware of the optimum inhalation manoeuver with their prescribed inhaler since incorrect inhaler usage is recognised as a major factor in worsening of disease outcomes. However, quite often inhalers are considered easy to use and patients do not receive adequate training even though it has been estimated that up to 68% of patients do not use their pressurised metered dose inhalers (pMDI) or dry powder inhaler (DPI) correctly.

At the same time, up to 67% of nurses, doctors and respiratory therapists are also unable to adequately describe or perform critical steps of inhaler use. These data point to an urgent need for better education as well as training and testing of patients’ inhalation manoeuvers. When evaluating the quality of individual inhalations, the measurement system draws on stored in vitro data and is able to estimate the aerosol quality released from the tested device depending on the inhalation manoeuver for each inhalation.

However, complex in vitro measurements are necessary to determine flow threshold values if new inhalation devices need to be incorporated into the system. With the algorithm presented in this paper, a new computer-based measurement system can be developed, which does not rely on extensive measurements but instead is based on published data. It therefore allows rapid adaptation to new inhalers and product innovations, provided that data exist and are accurately described in the literature.


The literature analysis revealed availability of robust data for the required inhalation flow characteristics for most devices and thus for the development of an algorithm. For those devices for which these parameters are not published, the minimum required flow criteria were defined based on published data regarding individual aspects of aerosol quality.


The technical characteristics of different inhalers and the delivery and deposition of the fine particle dose to the lungs may be important additional considerations to help the physician to select the most appropriate device for the individual patient to optimise their treatment. The gathered information in this review provides a comprehensive overview of inhalation systems available on the market regarding the requirements for an acceptable inhalation manoeuver and shows which goals should be achieved in terms of inhalation flows.

Although there are only a few possibilities in practice to measure patients’ inspiratory flow rates, prescribers should ensure that the patient can raise the required inspiratory flow rate to adequately operate the chosen inhalation device. The prescriber also has to be aware that the requirements for flow velocity, inhalation time and volumes should be reached. The performance of the patient (possibly depending on the severity of the disease) to achieve the required thresholds should be considered when selecting the inhaler.

The presented algorithm can be used to develop a new computer-based measurement system which could test all the above described flow parameters. Such a measuring tool could assist testing and training of patients’ individual inhalation manoeuvers with their specific inhalation devices.