In the field of bioethics, Aristotle's ethics does not have the same practical force as action-based theories, especially when the dilemma in question involves deciding whether or not to do some particular action ("pulling the plug" on a patient). In any case, there are two ways we can apply the character based approach to bioethics. First, the specific healthcare provider (nurse, doctor, etc.) could continually ask themselves "What kind of character do I want to have as a healthcare provider, and what actions are consistent with this character?". A healthcare provider can ask themselves whether a certain action reflects the kind of character they want to be associated with. On a more general scale, the healthcare industry itself could ask itself "What kind of character do we want associated with the healthcare industry and how would this particular action contribute or take away from that character?"
Secondly, for Aristotle a virtuous action is a "mean" between two extremes. For example, bravery is the middle-point between cowardice and foolhardiness. However, it is not always clear whether every action is a mean of this way. How would pulling the plug on a patient fit in Aristotle's golden mean analysis? I think the safest way to apply Aristotle's theory would be to emphasize character, rather than get lost in the thickets of golden mean analysis.
Using Aristotelian ethics to resolve particular cases is always difficult, because the question of "what ought I to do?" is always secondary to the question "what ought I to become?". After all, Aristotle himself admits that we should not expect precision in ethical matters.