Understanding pMDI's and spacers/VHC

The pressurized metered-dose inhaler (pMDI) was introduced to deliver inhaled medications in a convenient and reliable multi-dose presentation. The key components of the pMDI device and patient’s inhaler technique all play roles in determining drug delivery to the lungs. Even with optimal technique, however, pMDIs deliver, at best, only ∼20% of the emitted dose to the lower airways, leaving ∼80% in the oropharynx. Suboptimal technique may further reduce this fraction to zero. Poor coordination between activation of the pMDI with inhalation is a common critical problem too. Spacer or valved holding chamber (VHC) was developed to address some, but not all, of the problems when using a pMDI. The terms of spacer and VHC are not interchangeable. A spacer is an additional reservoir placed between the mouthpiece of the pMDI and the mouth of the patient while a VHC is a reservoir with a one-way valve permitting airflow into, but not out of, the patient’s mouth. Use of a spacer/VHC slows down the aerosolized particles emitted from the pMDI, which may further increase lung deposition of the respirable fine particles. The correct use of a spacer/VHC facilitates coordination between pMDI actuation and inhalation but some synchrony of activation of the pMDI with inhalation is still desirable. VHCs are not all the same. Each pairing of a pMDI plus VHC should be considered as a unique delivery system. Education on the correct use of spacer/VHCs with pMDIs is still important to avoid the potential for new errors introduced with the spacer/VHC.