After Anakin received mortal wounds on Mustafar, he was rescued, healed, and augmented into the incarnation of Darth Vader we all recognize.
Earlier in Episode III, Palpatine mentioned that Darth Plagueis's apprentice (Darth Sidious) learned everything from his master, implying also that he could keep people from dying.
Do we have any indication that this wasn't a bluff? If not a bluff, did Sidious use this power to keep Vader alive while the medical droids did their work? Or was it solely the work of the droids (or maybe medical personnel)?