Final answer:
The most appropriate course of action for a 5-year-old boy with a fever following an appendicectomy is to possibly open the wound for assessment and debridement, accompanied by diagnostic imaging like an abdominal USS, CT scan, or x-ray based on clinical judgment to diagnose and treat any further infections or complications.
Step-by-step explanation:
The most appropriate course of action for a 5-year-old boy who develops persistent fever following an open appendicectomy for gangrenous appendicitis, with symptoms of wound erythema and abdominal distension, is to conduct diagnostic tests that can best identify the source of infection and guide treatment. Given the clinical scenario, opening the wound may be necessary to assess for possible wound infection or abscess formation, as well as to afford the opportunity for debridement if needed. Meanwhile, imaging techniques such as an abdominal ultrasound (USS), CT scan, or x-ray can be helpful adjuncts to diagnose possible complications such as intra-abdominal abscess or other sources of infection, but the decision on which to use should be based on clinical judgment considering patient stability and available resources.
It's essential to act promptly to prevent further complications such as sepsis or spread of infection. Moreover, if there is suspicion of deeper or more extensive infection or if there is a lack of improvement with initial treatments, more advanced imaging like a CT scan could be warranted to guide further diagnosis and treatment.