A nurse is assessing a client for a suspected anaphylactic reaction following a CT scan with contrast media. For which of the following client findings should the nurse intervene first?

The correct answer is A: Stridor. Stridor indicates upper airway obstruction, which can rapidly progress to airway compromise and respiratory distress in an anaphylactic reaction. Therefore, the nurse should intervene first to ensure the client's airway is patent. Hypotension (B) is important but can be addressed after ensuring the airway is clear. Urticaria (C) and vomiting (D) are common signs of anaphylaxis but do not pose immediate life-threatening risks compared to airway compromise.