Which of the following increases the likelihood of medication delivery in inhalers?

Using spacers significantly increases the likelihood of effective medication delivery when using inhalers. A spacer is a device that attaches to the inhaler and holds the aerosolized medication in a chamber, allowing the patient to inhale it more effectively. This is particularly beneficial for individuals who may have difficulty coordinating their breathing with the activation of the inhaler.

Spacers help to ensure that a greater amount of the medication reaches the lungs rather than being deposited in the mouth or throat, which is a common issue when using metered-dose inhalers alone. By using a spacer, patients have more time to inhale the medication and can take a slow, deep breath, enhancing the medication's deposition in the airways.

Other options, such as mouthguards, nasal sprays, and chest physiotherapy, do not serve the same purpose in improving inhalation technique or enhancing the delivery of inhaled medication. Mouthguards are not designed for medication delivery, nasal sprays target the nasal passages rather than the lungs, and chest physiotherapy focuses on clearing mucus from the lungs rather than delivering medication.