Popa, in this case the patient is not refusing to drink. he has a medical condition that makes it hard for him to drink. he needs the line placed to get the proper nutrients.
remember that drinking on yom kippur is asur deorisa as well, its just that when someone’s life is in danger either a) there is a mitzva to be mechalel and save him or b) the mitzva is temporarily voided while you do what you need to do to save him
if someone is severely dehydrated, forcing them to drink is actually dangerous. but if one is at such a point of dehydration than they need to be hospitalized either way