Final answer:
The correct guideline for using a metered-dose inhaler is to press the canister while inhaling deeply and slowly, ensuring the medication is delivered to the lungs effectively.
Step-by-step explanation:
When educating an adolescent with asthma on using a metered-dose inhaler, the recommended guideline to follow is b) Press the canister while inhaling deeply and slowly. It is essential to coordinate the pressing of the canister with a slow and deep inhalation to ensure the medication is delivered effectively into the lungs. Additionally, it is advisable to exhale fully before placing the inhaler in the mouth and to shake the inhaler vigorously before each use to mix the medication properly. Asthma, a condition characterized by symptoms such as coughing, shortness of breath, wheezing, and chest tightness, often requires the use of inhaled medications, like bronchodilators, which are designed to ease the constriction of air passages.