Final answer:
The nurse should respond empathetically to a competent client's request to withdraw mechanical ventilation by asking 'Tell me how you are feeling' to encourage discussion about the patient's feelings and care preferences.
Step-by-step explanation:
In response to a client who is competent and requires long-term mechanical ventilation expressing a desire to have the ventilator withdrawn, the most professional and empathetic response by the nurse would be, "Tell me how you are feeling." This open-ended approach respects the patient's autonomy and provides a safe space for the patient to discuss their feelings and desires regarding their care. While the decision to withdraw life-sustaining treatment is complex and may involve legal and ethical considerations, it is important for healthcare professionals to listen to and acknowledge their patient's wishes, providing support and information.