Which symptom is a nurse most likely to monitor closely in a patient with heart failure?

Monitoring for orthopnea in a patient with heart failure is crucial because this symptom indicates difficulty breathing when lying flat. It occurs due to fluid accumulation in the lungs, which is a common issue in heart failure due to the heart's inability to pump effectively. When a patient lies down, blood flow to the chest increases, and if the heart cannot manage that volume, it leads to pulmonary congestion, causing shortness of breath.

Understanding this symptom is vital for assessing the severity of heart failure and the effectiveness of treatment. The presence of orthopnea often prompts further evaluation and immediate intervention to alleviate symptoms and prevent exacerbation. Recognizing and addressing this issue can significantly improve the patient's comfort and overall management of heart failure.

The other options, while potentially relevant in other contexts, do not directly correlate with the immediate monitoring needs commonly associated with heart failure. Increased appetite is not typically observed in heart failure; severe headaches may result from various causes unrelated to heart function; and diarrhea might occur for multiple reasons but is not a classic symptom to monitor in heart failure cases.