My grandpa had a partial knee surgery He is 86

Patient: My grandpa had a partial knee surgery. He is 86 years old. They noticed two small clots in his leg. A week after surgery he had a fairly significant altered mental status. He has gained weight and not eating so likely fluid. He is also mumbling at times and hard to understand. He was mentally intact prior to surgery. He is also now sleeping with his eyes half open which he never did before. He has developed shaking and unsteadiness.What are the likely reasons for all this?

Doctor: