What treatment involves the application of cold agents to reduce swelling and pain?

The correct treatment that involves the application of cold agents to reduce swelling and pain is cryotherapy. This method is commonly used in physical therapy and sports medicine for its effectiveness in managing acute injuries and postoperative swelling. The cold applications help to constrict blood vessels, which reduces blood flow to the affected area, leading to decreased inflammation and swelling. Additionally, cryotherapy helps numb the area, providing pain relief as it interrupts the pain-spasm cycle that can lead to prolonged discomfort.

In contrast, heat therapy would use heat to relax muscles and improve circulation, which is not ideal for swelling or acute pain. Electrotherapy involves the use of electrical currents to stimulate muscle contraction or nerve pathways, primarily for rehabilitation purposes. Ultrasound therapy utilizes sound waves to promote tissue healing and is not designed to apply cooling effects like cryotherapy does. Through this differentiation, it's clear why cryotherapy is the appropriate choice for reducing swelling and pain with cold applications.