The acronym MDI, frequently encountered in discussions about respiratory care, identifies a widely used medical device. It represents a highly precise method for administering pharmaceutical agents directly to the lungs. This small, portable technology plays a significant role in managing long-term breathing conditions and providing fast relief during respiratory episodes.
What MDI Stands For and Its Primary Role
MDI is the abbreviation for Metered-Dose Inhaler, a small, handheld device developed to deliver a fixed dose of medication in an aerosolized mist. The term “metered-dose” signifies that each activation of the device releases a specific, measured quantity of the drug. The primary function of the MDI is to deliver medication directly into the patient’s airways and lung tissue. By targeting the respiratory system, the device allows the medicine to act quickly and minimizes the systemic side effects that can occur with oral medications. This delivery system is most commonly prescribed for the management of chronic respiratory conditions, including asthma and Chronic Obstructive Pulmonary Disease (COPD).
How the Metered-Dose Inhaler Functions
The Metered-Dose Inhaler operates through a specialized mechanical system that converts a liquid drug formulation into a fine, breathable spray. The device consists of three main parts: a metal canister containing the medication, a metering valve, and a plastic actuator, which serves as the mouthpiece. The drug formulation inside the canister is suspended or dissolved in a liquefied gas propellant, such as hydrofluoroalkane (HFA). When the patient presses down on the canister, the metering valve is activated, releasing a precise volume of the drug and propellant mixture. This mixture is forced through a small nozzle in the actuator, which causes the propellant to rapidly expand and evaporate, creating the aerosol cloud of fine medication particles. The resulting mist contains particles sized specifically to deposit optimally within the lower airways and lungs.
Essential Steps for Correct MDI Usage
Effective MDI use relies heavily on proper patient technique, as poor coordination can significantly reduce the amount of medication reaching the lungs. Before administration, the inhaler should be shaken vigorously for five to ten seconds to ensure the drug and propellant are thoroughly mixed. If the inhaler is new or has not been used for a period, it must be “primed” by spraying a few test puffs into the air to ensure the metering valve is full and ready to deliver a full dose.
The patient must first exhale fully, moving air away from the mouthpiece, to empty the lungs before beginning the inhalation. As the patient starts to breathe in slowly through the mouth, they must simultaneously press down on the canister to release the medication. The inhalation should be slow and deep, ideally lasting between three and five seconds, to draw the aerosol deep into the lungs.
After the dose is inhaled, the patient should remove the inhaler and hold their breath for up to ten seconds to allow the small medication particles time to settle in the airways. If a second puff is required, the patient should wait approximately one minute before repeating the full sequence of shaking, exhaling, and inhaling. For patients using a corticosteroid MDI, rinsing the mouth with water and spitting it out immediately after use helps prevent local side effects like oral thrush.
Many healthcare providers recommend using a valved holding chamber, commonly known as a spacer, with an MDI to simplify the technique and enhance drug delivery. The spacer attaches to the MDI and holds the medication mist in a chamber, eliminating the need for perfect press-and-breathe coordination. This device slows the velocity of the aerosol spray and allows the patient to breathe in the dose over several breaths, which increases the amount of drug reaching the lower airways and reduces deposition in the back of the throat.