An inhaler spacer, often referred to as a Valved Holding Chamber (VHC), is an accessory device used with a Metered-Dose Inhaler (MDI) to improve the delivery of aerosolized medicine to the lungs. This device acts as a temporary reservoir for the medication spray, addressing common difficulties users have with coordinating the activation of the inhaler and the subsequent inhalation.
The Core Components of the Device
The standard spacer or VHC typically presents as a tube-like structure, often resembling a small, clear bottle or cylinder made from polycarbonate plastic or metal. This central component is known as the chamber, which provides the necessary volume to hold the medication cloud temporarily. The chamber’s interior is frequently treated with an anti-static coating to discourage medication particles from sticking to the walls before inhalation.
The device features two distinct openings on opposite ends of the chamber. At one end is the adapter, a socket designed to securely fit the mouthpiece of the MDI. The inhaler is inserted here, forming a seal so the medication spray is directed entirely into the chamber.
The other end terminates in the mouthpiece, which is usually a tapered oval shape intended for the user to place between their lips to create a tight seal for inhalation.
In the case of a Valved Holding Chamber (VHC), a one-way flap or disc known as a valve is positioned near the mouthpiece. This valve is generally a thin, translucent piece of material. Its purpose is to open inward when the user inhales, allowing the medicine to exit.
The valve closes when the user pauses or exhales, ensuring the medication remains suspended inside the chamber. Some models incorporate a small whistle or signal near the valve that indicates if the user is inhaling too rapidly.
Key Design Variations and Accessories
Spacers vary noticeably in size, primarily defined by the volume of the chamber. Smaller volume spacers, like those with a capacity of around 135 milliliters, are shorter and more compact for portability. Larger volume chambers can hold up to 750 milliliters and are significantly longer and bulkier.
A major visual difference appears when the device is equipped with a mask attachment instead of a standard mouthpiece. This soft, often rubberized or silicone facial mask replaces the mouthpiece and is designed to fit snugly over the nose and mouth.
Mask variations are manufactured in different sizes, including infant, child, and adult. They are typically used for individuals who cannot reliably form a tight seal around the mouthpiece. The addition of a mask gives the device a broader, more rounded appearance at the patient end.
Collapsible Spacers
Another variation is the collapsible spacer, designed for enhanced portability. These devices are often constructed from folding plastic or specialized paperboard, appearing flat or disc-shaped when not in use. When extended for medication administration, they pop up into the familiar tubular shape, offering a practical solution for travel.
Visualizing the Mechanism: Why Spacers Look the Way They Do
The tubular, elongated shape of the chamber is directly related to the physics of the medication cloud released by the MDI. When an inhaler is actuated, the medicine is ejected at a very high velocity, propelled by a gas that quickly evaporates.
The length of the chamber provides the necessary distance and time for the propellant to evaporate fully and for the fast-moving aerosol particles to slow down. This deceleration allows the larger, heavier medication particles to deposit on the chamber walls rather than impacting the back of the throat.
Only the finest, most respirable particles remain suspended to be inhaled. This increases the amount of drug reaching the lungs and reduces potential side effects in the mouth and throat. The clear material of the chamber allows users to visually confirm that the dose has been sprayed and is suspended within the chamber.
For Valved Holding Chambers, the visibly thin, low-resistance flap of the one-way valve permits easy opening even with a gentle breath. This design traps the medication inside, allowing the user to take multiple breaths to fully clear the chamber without losing the dose or accidentally exhaling back into the device. The visual confirmation that the valve is moving with each breath provides a simple way for users and caregivers to monitor correct inhalation technique.