What Causes Hallucination In A Cancer Patient While On Dilaudid?

My husband is currently in the hospital suffering from bladder cancer. A pain pump has been installed to ease the pain in the pelvic area/left leg which is being caused by the tumor pressing on the pelvic nerves. The pain pump seems to be working, but the surgery has now caused the right leg to become weak/with major pain that makes it impossible to stand or walk. They are treating this issue with 2 to 6 MG of Dilaudid which is causing him to hallucinate, have major twitching, sleeps most of the time. The pain pump is constantly pumping 2 MG of Dilaudid all the time. Is there any other medication that might help with the issues with his right leg, so he is not in a zombie state all the time?