Delirium may come on over a few hours or several days. Experts think delirium is caused by a change in the way the brain is working. Something either decreases the supply or use of oxygen in the brain or changes the chemicals in the brain. Although poor vision and hearing do not cause delirium, they make it more likely that delirium will occur. This is especially true when older adults are in surroundings that are strange to them.
Medications are the most common cause of delirium.
The older adult may be taking many drugs, high doses of drugs, or drugs that are harmful when taken together. Also, the aging body does not process drugs as well as it used to because of changes in the liver and kidneys. Even cold medicines sometimes cause confusion. Almost any medical illness can lead to delirium. Infections in the lungs and bladder or kidneys are also common causes.