Valved holding chambers (VHCs) for use with pressurised metered-dose inhalers (pMDIs): a review of causes of inconsistent medication delivery.

BACKGROUND: Valved holding chambers (VHCs) are prescribed with pressurised metered dose inhalers (pMDIs) to improve medication delivery for the treatment of respiratory diseases because they reduce the need for the patient to co-ordinate inhaler actuation with the onset of inhalation. Although mechanically robust and clinically effective if properly designed and pre-conditioned, there are several causes of inconsistent medication delivery if this is not the case. These include: electrostatic charge; incorrect operation of inhalation and exhalation valves; and the fit of the facemask - where present - to the face. In addition, behavioral factors, such as not following patient instructions for use and maintenance, and imperfect breathing technique, amplify overall variability. Aids such as valve movement indicators that provide patient feedback are helpful in order to minimise these factors.
METHODS: This article reviews recent literature concerning the causes of inconsistent drug delivery and the improvements that have been made by manufacturers to VHC devices, and assesses the clinical implications. The attributes of a well-designed VHC are summarised.