Biomedical Engineering Reference
In-Depth Information
Table 4.2 Factors that should be considered in CI day-to-day use ( Adapted from [ 3 ]— used by
permission )
Routine CI setup and operation
Factor potentially affects
Cause(s)
MB
APSD
Locating collection surfaces
Man/machine
Ye s
Ye s
Accounting for collection
surfaces and final filter
Man
Ye s
Ye s
Assertion of stage order
Man
No
Ye s
Air leakage into CI/MSLI
Man/machine
Yes, unless wall losses
are accounted for
Ye s
Poor seal and orientation
between induction port/
pre-separator/CI
Man/machine
No
No, unless
the leak is
massive
Improper alignment between
inhaler mouthpiece and
induction port
Man
No
Ye s
Inadequate liquid volume or
liquid missing from
liquid-based collection
surfaces
Man
Yes, due to analytical
procedure differences
Ye s
CI/MSLI flow rate
Man
Not normally, but consider for
highly flow-rate-dependent
DPIs if tested at flow rates
different to dose content
uniformity testing
Ye s
Timer operation of two-way
solenoid valve for DPI
testing and MDIs with
integrated spacers
Man/machine
Ye s
Ye s
Cleaning of stage nozzles
Man
Ye s
Ye s
Worn/corroded stage nozzles
Machine
No
Ye s
Insufficient or excessive number
of inhaler actuations
Man
Ye s
Ye s
Improper sample recovery
Man
Ye s
Ye s
Electrostatic effects
Machine
Ye s
Ye s
The need for a failure investigation tree for the cascade impaction method rein-
forces the complexity of the procedure and brings into question why an alternative
approach has not become the accepted norm by stakeholders involved in the testing
of OIPs. The lack of an alternative measurement technique having similar capability
in terms of traceability to the aerodynamic diameter size scale and, at the same time,
specificity for mass of API are the main reasons why this relatively historic method
for aerosol analysis remains the standard approach. The search for more rapid and
easy-to-use measurement apparatuses together with a more effective data analysis
technique has been one of the driving forces underlying the development of the
methodologies that are discussed later in this topic. Although alternatives to
CI-based measurement of OIP APSD exist and are widely used, particularly in the
research and development environment, with few exceptions, none of the techniques
 
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