Final answer:
The nurse's priority when admitting an infant with heart failure is to address the most critical issues first. A respiratory rate of 20/min is concerning and indicates possible respiratory distress, which is a life-threatening condition that requires immediate attention.
Step-by-step explanation:
When admitting a 4-month-old infant with heart failure, the nurse's priority should be to assess and address the most critical and life-threatening findings first. From the options provided, the finding that requires immediate attention would be a respiratory rate of 20/min, as this is lower than the normal expected range for an infant and could indicate respiratory distress. This is especially concerning in the context of heart failure, where adequate oxygenation is crucial. The presence of pink wound tissue with no drainage (Option A) and a prealbumin level of 12 mg/dL (Option D) are less immediately concerning, while yellow wound tissue with purulent drainage and foul odor (Option B) could signify an infection, which should also be addressed promptly but might not be immediately life-threatening as the abnormal respiratory rate.