Spacer devices are also known as add-on devices, accessory devices, extension devices, and holding chambers. They are attachments to pMDI actuators, with volumes ranging from 20 mL to 750 mL in commercially available models. Spacers perform several functions. By placing some distance (and, thus, time) between the point of aerosol generation and the patient’s mouth, they reduce oropharyngeal deposition and increase lung deposition. Spacers make pMDI’s easier to use by reducing or eliminating the need for coordination between actuation and inhalation, and reducing the cold effect. These benefits are achieved at the expense of making the pMDI system substantially larger and less convenient.
Some spacer devices have universal adaptors that allow them to be used with any pMDI actuator mouthpiece, while others have rigid adaptors that will only fit one shape of mouthpiece. These design features are sometimes reinforced by consideration of whether the spray from a particular pMDI matches the shape of the spacer, but may also be influenced by marketing considerations.