In the medical context, MDI universally stands for Metered-Dose Inhaler, a small, handheld device used in the management of chronic respiratory conditions. This device is designed to deliver a precise, pre-measured dose of medication directly into the lungs to achieve a therapeutic effect. The MDI is a highly portable and effective tool, but its success relies heavily on the user mastering the specific technique required to coordinate its activation with their breathing.
What is a Metered-Dose Inhaler?
A metered-dose inhaler is a device engineered for the aerosolized delivery of medicine directly to the airways and lungs. This targeted approach is highly effective because it bypasses the digestive system and minimizes the systemic side effects that can occur with oral medications. The small, pressurized canister within the inhaler holds a suspension or solution of the drug, which is released as a fine mist when the device is actuated.
MDIs are used to treat common conditions like asthma and chronic obstructive pulmonary disease (COPD). The medications delivered typically fall into two main categories: bronchodilators, which act quickly to relax the muscles around the airways (often called “rescue” inhalers), and corticosteroids, which reduce inflammation over time and are used for maintenance or “controller” therapy. Some MDIs contain a combination of both types of drugs to provide both immediate relief and long-term control.
How MDIs Deliver Medication
The function of an MDI depends on three primary components working together: the metal canister, the metering valve, and the actuator, or mouthpiece. The canister holds the medication suspended in a liquefied gas propellant, which is typically a hydrofluoroalkane (HFA) compound. When the user presses down on the canister, the metering valve is briefly opened, releasing an exact, measured volume of the drug formulation.
This precise volume is forced out of the device’s nozzle as a high-velocity spray. The HFA propellant rapidly evaporates upon release, which breaks the medication into the micro-sized particles required for deep lung penetration, creating a visible aerosol plume. The speed and consistency of this aerosolization process are crucial for ensuring that a reliable and reproducible dose is delivered.
Maximizing MDI Effectiveness Through Proper Technique
Achieving maximum benefit requires mastering specific coordination, as only about 10–20% of the medication reaches the lungs even with perfect technique. Proper use begins with shaking the MDI several times to ensure the medication is evenly mixed before removing the mouthpiece cap. The user should exhale fully to empty the lungs before placing the mouthpiece in their mouth.
The most challenging step is coordination: the user must begin a slow, deep inhalation just as they press down on the canister to release the medication. This slow breath must continue for three to five seconds to carry the aerosol deep into the lungs. After inhaling, the user should hold their breath for up to ten seconds, allowing the drug particles to settle in the airways.
A common error is inhaling too quickly, which causes the medication to impact and deposit in the back of the throat and mouth, reducing the amount delivered to the lungs. Failing to coordinate the press and the breath is another frequent mistake. For those using corticosteroid medications, rinsing the mouth after use is important to minimize the risk of developing oral yeast infections.
To overcome coordination difficulty, a spacer or valved holding chamber is recommended. This device is a tube that attaches to the MDI, acting as a reservoir for the aerosolized medication. The spacer slows the velocity of the spray and allows the medication to turn into a finer mist. Using a spacer increases the amount of drug reaching the lower airways and significantly reduces the amount deposited in the throat.