A metered-dose inhaler (MDI) is a handheld device that delivers a precisely measured dose of medication, usually a bronchodilator or a corticosteroid, as a fine mist directly into the lungs. This device relies on a propellant to spray the drug from the canister through the mouthpiece and into the airways. While a spacer, which is a tube attached to the inhaler, is the preferred method for increasing the amount of medicine that reaches the lungs, it is sometimes unavailable. Using the MDI directly requires a highly specific technique to ensure the medication is delivered effectively and maximize the therapeutic effect when a spacer cannot be used.
The Essential Closed-Mouth Technique
Effective use of the MDI begins with preparation. Shake the inhaler vigorously for at least five to ten seconds before each use to ensure the medicine and its propellant are thoroughly mixed. Before placing the inhaler in the mouth, the user must exhale completely to empty the lungs, creating the necessary space to draw in the medication deeply.
The mouthpiece is then placed between the teeth and above the tongue, and the lips must be closed tightly around it to form a seal. This tight seal prevents the aerosolized medication from escaping into the surrounding air upon actuation. As the user begins a slow and deep inhalation, they must press down firmly on the canister to release a single puff. The inhalation should continue for three to five seconds, drawing the medication mist deep into the airways.
The coordination of pressing the canister and starting the inhalation is the most challenging part of this technique, as the medication is released quickly. After inhaling fully, the inhaler should be removed from the mouth. The user must then hold their breath for up to ten seconds to allow the small medication particles to settle in the lungs. Holding the breath for this period significantly increases the amount of drug absorbed.
The Open-Mouth Method for Reducing Throat Deposition
The open-mouth method is an alternative technique specifically designed to reduce the amount of medication deposited in the mouth and throat. This occurs because the medication travels a longer distance before it is inhaled, allowing the propellant to dissipate and the larger drug particles to slow down.
Instead of sealing the lips around the mouthpiece, the inhaler is held approximately one to two inches away from the open mouth. The inhaler should be angled slightly toward the back of the throat to direct the spray. The technique still requires the user to exhale fully away from the device before starting. As the patient starts a slow and deep inhalation, the canister is pressed to release the puff.
The timing of the actuation and inhalation is even more critical with this method since there is no seal to trap the medicine, which increases the chance of the dose being lost to the air. The patient must then hold their breath for ten seconds to maximize the lung deposition of the inhaled drug.
Common Mistakes and Post-Use Safety
Common Mistakes
Several common errors can compromise the effectiveness of a metered-dose inhaler, even when the technique appears correct. One frequent mistake is inhaling too quickly, which causes the medication to impact and deposit on the back of the throat instead of traveling to the lower airways. Another error is failing to exhale fully before use, which limits the volume of air, and therefore the dose, that can be drawn into the lungs. Not shaking the inhaler before each use is also a common oversight that results in an inconsistent mixture of drug and propellant, leading to an incorrect dosage.
Multi-Dose Timing
For patients who require more than one puff of medication, the timing between subsequent actuations is important. After the first puff and the required breath hold, the user must wait at least 30 to 60 seconds before repeating the process, starting again with shaking the inhaler. This waiting period allows the propellant to reload and ensures the second dose is fully effective. Taking multiple puffs too quickly without waiting and shaking in between can lead to ineffective dosing and wasted medication.
Post-Use Oral Hygiene
A mandatory safety step, particularly for those using steroid-based inhalers, involves post-use oral hygiene to prevent a fungal infection known as oral candidiasis, or thrush. After completing the full dose, it is necessary to rinse the mouth thoroughly with water and gargle. The water must then be spit out and not swallowed, which helps remove any residual corticosteroid particles from the mouth and throat.