Final answer:
Electrocautery is used to relieve pain and reduce the risk of infection in a child's subungual hemorrhage by draining accumulated blood under the nail and preventing bacterial buildup.
Step-by-step explanation:
The statement regarding the rationale for using electrocautery to treat a child's subungual hemorrhage after a jar fell on the foot is most accurately described by option (a): It's used to relieve pain and reduce the risk of infection. This method involves the application of a controlled amount of electrical current to burn or destroy tissue, specifically the hematoma (collection of blood) under the nail, by creating a small hole in the nail. This allows the blood to drain, which alleviates pain caused by pressure from the accumulated blood. It also prevents the potential buildup of bacteria, which can lead to infection. Electrocautery can thereby expedite symptom relief and minimize complications that may arise from the injury.