After demonstrating how to use an incentive spirometer, what should a therapist instruct the patient to do?

Instructing the patient to take a deep breath through the mouthpiece is the appropriate action after demonstrating how to use an incentive spirometer. This device is used to encourage the patient to take slow, deep breaths in order to expand their lungs and prevent complications such as atelectasis following surgery or prolonged bed rest.

By taking a deep breath through the mouthpiece, the patient creates enough negative pressure to properly activate the spirometer, allowing them to measure the volume of air they can inhale. This action confirms they are using the device correctly and helps motivate the patient as they can visibly see the volume of air inhaled, encouraging adherence to the practice.

The other options do not effectively capture the purpose of the incentive spirometer. For example, exhaling through the device or exhaling completely before inhaling does not align with the goal of promoting inhalation. Breathe in to inspiratory capacity is slightly off as it doesn't specify the deep breath through the mouthpiece, which is essential to engage the patient's understanding properly.