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metered-dose inhaler (MDI),
metered-dose inhalerA device used to deliver a specified number of doses of a therapeutic inhalant—e.g., a beta-agonist for asthma.
metered-dose inhalerPharmacology A device used to deliver a specified number of doses of a therapeutic inhalant–eg, β-agonist for asthma
Synonym(s): metered-dose inhaler.
metered-dose inhalerAbbreviation: MDI
When used correctly, a metered-dose inhaler can deliver accurate doses of medication to the respiratory tract. The MDI is a drug canister in an L-shaped mouthpiece, which can be used alone or with a “spacer” (a holding chamber designed to aerosolize medication so it can reach the lower respiratory tract). The health care professional teaching the patient proper MDI technique should gather the drug canister and mouthpiece, the package insert, and the spacer (if one is to be used). The MDI should be sprayed once or twice prior to initiating use, and the spacer inspected for foreign objects. The patient should wash his/her hands thoroughly, and may either sit or stand. If a peak flow meter is being used, the patient should take a reading prior to using the MDI. The patient should then clear the throat and nasal passages. The patient should hold the inhaler upright and shake it as directed, then remove the cap and hold the inhaler with the canister on top and the mouthpiece facing the patient's open mouth at the bottom. Tilting the head back slightly, the patient should breathe out slowly and completely. (When using an MDI with a spacer, the inhaler cap is removed and the mouthpiece is firmly inserted into the spacer, then the spacer and inhaler are held together upright and vigorously shaken 5 or 6 times. The space cap is then removed, the head tilted back, and the breath let out slowly and completely.) The inhaler mouthpiece may be positioned in one of two ways: 1 to 2 inches (2.5 to 5 cm) in front of the open mouth, mouth open; or with the mouthpiece in the mouth and lips sealed around it. However, this latter technique is less efficient in delivering medication and should never be used for steroids. While breathing in slowly, evenly, and deeply though the mouth, the patient should press once on the canister and continue inhaling for 3 to 5 sec. The breath should then be held for 10 sec (or as long as possible), allowing the medication to settle in the lungs. The inhaler should be removed from the mouth prior to exhaling. If a spacer is used, the patient should place the spacer mouthpiece in the mouth and seal the lips around it, then press on the canister to spray a puff of medication into the spacer and begin inhaling slowly through the mouth for 3 to 5 sec. The breath should then be held for 10 sec (or as long as possible). The spacer should be removed from the mouth prior to exhaling. If more than one puff is prescribed, the patient should wait 1 to 2 min between puffs to help the second puff to better penetrate the lungs. The patient should be taught to remember “B before C” when using an inhaled bronchodilator and corticosteroid; first inhaling the bronchodilator, waiting about 5 min, and then inhaling the corticosteroid. This helps to open the air passages for maximum absorption of the steroid. After inhaling a corticosteroid, the patient should rinse the mouth with water and expectorate it.
The spacer and the L-shaped mouthpiece and cap should be rinsed with warm, running water at least once each day, and washed with warm soapy water, then rinsed at least once each week. The equipment should always be allowed to air-dry. The patient can calculate how long a drug canister will last by reading the total number of doses on the label, counting the number of puffs used each day, and dividing the total doses by the number of daily puffs. (Thus if a canister contains 200 doses and the patient takes 8-10 each day, a new canister will be required in a month). The health care educator should provide the patient with written instructions and illustrations for proper MDI use. The patient also should be taught about (and provided with) information on the desired effects of each medication and the possible adverse reactions. The teaching session, the patient's demonstration of the method, and any questions raised should be documented in the patient's record.