Specifications of Spacer Devices

At present, spacers are not considered to be medical products and can therefore be marketed without any documentation. The performance characteristics of pMDIs are required to be strictly documented before approval by drug regulatory authorities considering the significant influence of spacers on pMDI performance, it would seem logical to require similar documentation of the pMDI-spacer combination before approval and marketing. Spacers should not be considered generic devices that can be used with any pMDI. In the future, spacers should be tested for their effect on aerosol delivery with specified pMDIs and marketed only for use with these pMDIs. 

In Vitro Measurement of Delivered Doses from Spacers 

The delivered dose from spacers is sometimes reported as the dose at the time of pMDI actuation—i.e., the dose is measured in vitro by emptying the spacer immediately upon pMDI actuation. This, however, does not take account of the delayed emptying by children with variable and shallow breathing maneuvers. The aerosol is lost passively during such a period between actuation of the pMDI and in vivo emptying of the spacer (Fig. 1). Since the aim of a spacer is to provide a stable aerosol to avoid the need for coordination between actuation and inhalation, dose measurement concomitant with actuation of the pMDI seems irrelevant. The dose from the spacer should be defined after a period of 10 or 20 s, which would be a more realistic reflection of the situation in clinical use. The passive loss of aerosol is monoexponential and can be described by its half-life (24). 

Marcel Dekker, Ino. 270 Madison Avenue, New York, New York 10016 

One of the aims of spacer devices is the removal of large aerosol particles. However, the loss of fine particles reduces the cost-effectiveness of treatment (15). Furthermore, such losses may be variable, leading to unpredictable dosing and disease control. 

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