Final answer:
The most concerning symptom of hypercalcemia in a patient with cancer and bone metastasis is cardiac changes, as it is potentially life-threatening and requires immediate attention.
Step-by-step explanation:
When analyzing symptoms of hypercalcemia, a medical condition characterized by elevated blood calcium levels, the symptom that would cause a nurse the most concern in a patient with cancer and bone metastasis is cardiac changes. Hypercalcemia can affect various body systems, with cardiac changes being potentially life-threatening. Lethargy, sluggish reflexes, constipation, loss of appetite, and confusion are also associated with hypercalcemia, but cardiac changes, such as arrhythmias and potentially heart failure, require immediate attention to prevent severe complications or death. The nurse's concern is heightened when a patient exhibits cardiac changes because they can have direct and immediate impacts on the patient's survival and require urgent intervention.