Delirium

Physical illnesses cause delirium by acutely disrupting the normal metabolism of the nerve cells in the brain. This can come about by reducing the oxygen supply (e.g., cardiac failure, a fall in blood pressure, anemia), by physiological disturbances (e.g., fever, liver or kidney failure, endocrine disorders), by the action of drugs and toxins, and by direct damage (e.g., stroke, head injury). The most common causes of delirium in elderly patients are acute infections (particularly of the chest and urinary tract), and the prescribed drugs that they are taking. Almost any drug can cause delirium in an elderly patient, but some are particularly associated with this problem, either because they act directly on the brain (e.g., tranquilizers, anticonvulsants), or because they are broken down and eliminated less efficiently by the elderly body and so accumulate, or because they have particular modes of action. Drugs with anticholinergic activity are particularly liable to cause delirium, which has led to the suggestion that disturbance of the cholinergic nerve systems in the brain is an important feature of the pathology of delirium. In practice, elderly patients are often taking many drugs, and delirium may occur as a cumulative effect of this polypharmacy rather than it being due to one drug acting alone. It is important to bear in mind that delirium can also be caused by the sudden withdrawal of a drug upon which the patient is physically dependent. The most common drug in this respect is alcohol, although in elderly patients other possibilities, such as opiate analgesics and benzodiazepines, should be considered. Although delirium usually has a physical cause, it is recognized that, in particularly vulnerable individuals, a severe psychological stress such as bereavement, relocation, or extreme sensory deprivation may be sufficient to precipitate it.