What is a spacer? What is a holding chamber?
Metered dose inhalers (MDIs) for asthma medications typically consist of a metal aerosol canister (containing the medication and a propellant) in a plastic sleeve with a mouthpiece. The patient inhales one or more metered doses of a medication through the mouthpiece. Most people find it difficult (at least initially) to time the spraying of an MDI and the inhalation of the medicine: the patient must exhale fully and inhale and release the metered dose just at the beginning of the inhalation so as to draw the medication as fully and deeply into the lungs as possible. All too often the puffs are mis-timed and only make it part of the way into the airways, and some of the medication is invariably deposited into the mouth and on the back of the throat instead of into their lungs. In addition to being less effective, this can lead to other side effects (e.g., for inhaled steroids, an increased potential for thrush, an oral fungal infection described in section 2.3.3.). Several devices have
