Final answer:
The nurse will use Root cause analysis (RCA) to determine the cause of the patient's death after open heart surgery due to septicemia.
Step-by-step explanation:
When a patient dies after open heart surgery due to septicemia, a tool that the nurse can use to determine the cause of death is Root cause analysis (RCA). RCA is a systematic process that aims to identify the underlying causes of an event or problem. In this case, the nurse would investigate the factors that contributed to the development of septicemia, such as the sterilization procedures, infection control measures, and patient care practices, to identify any potential failures or gaps in the system.