Final answer:
The decision to terminate enteral feeding for a patient in a persistent vegetative state, based on their advance directive, is primarily guided by the ethical principle of autonomy.
Step-by-step explanation:
The decision to terminate enteral feeding for a patient in a persistent vegetative state, based on their advance directive, is primarily guided by the ethical principle of autonomy. Autonomy is the principle that individuals have the right to make decisions about their own healthcare. In this case, the patient's wishes as expressed in the advance directive take precedence.
The other ethical principles mentioned - justice, beneficence, and nonmaleficence - are also important in healthcare decision-making, but they may not be the primary basis for the decision to terminate enteral feeding in this particular situation.