Final answer:
The finding that warrants immediate intervention by the nurse is hypotension and fever (option B).
Step-by-step explanation:
A male client with ulcerative colitis who stopped taking a corticosteroid medication 6 days ago may experience various side effects. However, the finding that warrants immediate intervention by the nurse is hypotension and fever (option B). This combination of symptoms may indicate a serious infection or sepsis, which requires immediate medical attention.