Delirium is a transient syn? drome consisting of an altered level of conscious? ness and memory impairment, perceptual disturbance, or both that develops over a short time and fluctuates in severity during the course of the day. According to die Diagnostic and Statistical Manual of Mental Disorders, fourth edition, The essential feature of a delirium is a distur? bance of consciousness that is accompanied by a change in cognition that cannot be better accounted for by ? preexisting or evolving dementia [emphasis added].1 Delkium?formerly known as acute confusion?can