Metered-Dose Inhalers Print E-mail



Beta-stimulators (as well as anticholinergic and steroid drugs) can be inhaled as an aerosol using a metered-dose inhaler (MDI). This is a handheld, pressurized cartridge type of device in which the drug is either carried in a propellant gas (such as freon), or turned into a spray by passing a stream of air over a solution containing the drug. The MDI's advantages are its easy portability and its ability to deliver a fixed dose of medicine. Its disadvantage is the degree of coordination needed to get the most effective amount of medicine into the lungs. This means that anyone who has difficulty coordinating complex maneuvers cannot use this technique effectively. (Then a home nebulizer should be used. This larger unit does not require any dexterity. Patients simply breathe their medicine from it for several minutes.)

Another frequent handicap to using an MDI effectively is not knowing the proper technique. This is the proper way to use a hand-held MDI: hold the device right in front of your open mouth. Do not close your lips tightly around the mouthpiece no matter what the written instructions say! Then blow out all the air that you can, and depress the MDIwhich automatically releases the right amount of medicineas you start breathing in. Slowly keep the inhalation going (think of slowly sipping hot soup from a big spoon). Then hold your breath for 10 seconds. Then slowly breathe out.

No matter how good you are at using an MDI, though, most of the medicine ends up on the back of your throatperhaps as much as 90%. It is absorbed through the surface of the mouth and throat instead of reaching the lungs directly. One reason for this is that the medicine jets out too fast. An ineffective solution to this problem is holding the MDI one or two inches away from your mouth. This just makes coordination harder.

What we find really helps is to use a spacer between the MDI and your mouth. A spacer is simply a tube about three inches long and about two inches wide. Because it slows the speed at which the medicine travels before it enters your mouth, evaporation makes the aerosol droplets smaller and so able to penetrate deeper into the lungs. This kind of aid has been shown to deposit more of the medicine in the lungs more effectively.

A practical problem in using an MDI is not knowing when it is almost empty and your prescription needs renewing. There is a way! Place your MDI cartridgethe part containing the medicinein a glass of water. If the MDI sinks, it is full; if it floats fully submerged, it is three-quarters full; if the bottom breaks the top of the water, it is one-half full; if more shows, it is one-quarter full; and if it floats horizontally, it is empty.

The dispenser in which the MDI cartridge fits should be cleaned periodically. One technique involves an initial cleaning with liquid detergent and hot water, then soaking the dispenser for 30 minutes in a solution that is one-half water and one-half white vinegar. Dry with a towel afterwards. The tip of the MDI cartridge should simply be rinsed in hot running water after each day of use.


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