Final answer:
The key intervention is to provide supplemental oxygen to address the immediate life-threatening issue of hypoxia for the older woman with end-stage metastatic breast cancer.
Step-by-step explanation:
The most important intervention for a nurse to implement for an older woman with end-stage metastatic breast cancer, experiencing shortness of breath and confusion, with arterial blood gases indicating hypoxia, is to provide supplemental oxygen. The patient's symptoms suggest she is suffering from a severe lack of oxygen in the blood, which can lead to tissue damage and exacerbate her confusion.
Ensuring proper oxygenation is critical for maintaining bodily functions and preventing further decline. Although the patient is refusing to eat and is asking to go home, addressing the immediate life-threatening issue of hypoxia takes precedence. Following oxygen therapy, additional interventions can be considered to manage her other symptoms and support her quality of life as much as possible.