Final answer:
The most appropriate intervention would be referral to a specialist for further evaluation and management.
Step-by-step explanation:
The most appropriate intervention after initiation of treatment for otitis media in an 18-month-old child with a bulging, immobile tympanic membrane and a grade II/VI systolic murmur at the left sternal border would be referral to a pediatric specialist for further evaluation and management.
Otitis media is an infection of the middle ear that may cause symptoms such as bulging tympanic membrane, fever, and ear pain. In this case, the presence of a systolic murmur suggests a potential cardiac involvement, which requires detailed cardiac evaluation.
It is important to assess for any complications or underlying conditions associated with the symptoms presented by the child and to ensure appropriate management by a specialist.