I'm trying to find a horror movie that I saw in the 80's?

Guests arrived at this countryside mansion inn or hotel but when anyone tried to leave, he or she couldn't. They were trapped and dying one by one. One character chokes on a bone at dinner and one of the servants, a woman slits man's throat in front of everyone and takes the bone out . Pretty gory. Another woman goes for a swim in the pool and drowns when the pool's top is closed by some sort of a gl cover. One couple tries to drive escape away from this eerie house only to end up back in the drive way. At the end...there's some sort of a creature that is kept alive by human blood that is feed intravenously. That's why the guests are needed...to keep this thing alive. You see him in some sort of hospital bed, with tubes all over him and protected by some sort of plastic covering that surrounds the bed. Help!