The diagnosis of delirium is clinical. The DSM-V criteria for defining delirium are [3,4]:

  • Disturbance of consciousness i.e. reduced clarity of awareness of the environment, with reduced ability to focus, sustain or shift attention
  • A change in cognition such as memory deficit, disorientation, language disturbance or the development of a perceptual disturbance.
  • The presence of a general medical condition – In practice this is usually assumed rather than specified in each case.

NICE guideline [2] describes delirium, also known as ‘acute confusional state’, as disturbed consciousness, cognitive function or perception with an acute onset and fluctuating course. It develops over a short period of time, usually over a couple of days, and may lead to poor outcomes [2].

Three clinical subtypes of delirium are recognised: Hypoactive, Hyperactive and Mixed [2].

Subtype Feature
  • Heightened arousal
  • Restless
  • Agitated and sometimes aggressive
  • Decreased alertness
  • withdrawn
  • Quiet and sleepy

Key features of delirium [1]:

  • Recent onset of fluctuating awareness
  • Impairment of memory and attention
  • Disorganised thinking