Delirium

-Serious neuropsychiatric condition characterised by acute onset of fluctuations in consciousness, cognitive function, and perceptual disturbances (such as hallucinations)

-Unhelpfully, it is often called a number of different things – encephalopathy, delirium, sun-downing, and is often just called ‘confusion’

-Diagnostic guidelines state:

  • Disturbance of consciousness (used to be very vague, but now defined as attentional impairment)
  • Change in cognition (memory disturbances, disorientation, language disturbance) or perceptual disturbance (hallucinations, delusions) that is not accounted for by pre-existing dementia (I would also add diseases such as depression and psychosis)
  • Disturbance is caused by direct physiologic consequences of a medical condition – so it is differentiated from delirium due to drug intoxication or alcohol withdrawal
  • It is important to note that delirium can be hypoactive as well as hyperactive. The vast majority of patients that are delirious are not agitated or pulling out lines, they are drowsy in bed with no idea where they are

-The risk factors for delirium are pretty well-defined, there is an interaction of predisposing factors and precipitating factors that combine to produce delirium

  • Predisposing factors (pre-existing personal variables): age, pre-existing dementia or cognitive impairment, hearing or visual impairment, benzodiazepine use prior to hospitalisation, alcohol or drug dependence, chronic renal/liver disease
  • Precipitating factors (acute insults): increasing illness severity (multi-organ failure), electrolyte imbalance/metabolic disturbance, dehydration, malnutrition; sepsis; hypoxia or respiratory distress; neurological injury; trauma (including surgery), and pain.
  • Medications play a huge role – benzodiazepines, opiates, and propofol are all highly associated with delirium. Often midaz or propofol are used to control agitation, and although they may be necessary, prolonged and inappropriate use can put a patient into delirium or prolong it.

-We don’t quite understand the mechanism of delirium – it is clearly something that a variety of different factors can feed into. However, the best understanding currently is that the body enters an exaggerated stress response, which can disrupt the hypothalamic-pituitary axis, and leads to disruption of several neurotransmitter systems, particularly GABA and acetylcholine

  • This is important, as propofol and benzos are GABA agonists. One reason they think Dex may be better for preventing delirium is that it works through a different neurotransmitter system.

-It is estimated that up to 40% of patients are delirious upon admission to hospital, and among hospitalised patients the prevalence can range up to over 50%

  • Patients that are particularly vulnerable are elderly patients (particularly post-op) and ICU patients – there is some overlap in risk factors, but clearly there are often different issues going on, and different challenges for detection
  • It’s estimated that anywhere up to 80% of patients become delirious in the ICU – however this is really pretty dependent on the patient population, and from what I have read, it tends to average out to around 30%
  • Because it is so common in ICU, it is almost just accepted as an inevitable part of patient care and has been known at different times as “ICU psychosis”

-The real issue with delirium, and why we can’t just treat it as a part of the ICU experience, is that it is highly related to a heap of bad outcomes (even after controlling for illness severity and other patient factors)

  • It is independently associated with length of ICU and hospital stay, length of mechanical ventilation, increased use of restraints, and increased risk of falls, infections, and attempted self-extubation.
  • Most importantly, ICU patients that develop delirium are 2-3 times more likely to die in the ICU than those that don’t develop delirium; and after discharge mortality at 12 months is reported to be 42%, compared to 15% for patients that were never delirious.
  • Delirium has also been associated with lasting cognitive impairment, or with quick cognitive decline – this has been reported in over 70% of patients surviving ICU delirium

-One huge problem is that delirium is very under-recognised – with some studies placing this figure at 60-85% of cases.

  • The reasons for this vary depending on the patient population – in elderly pts it is differentiating delirium from dementia; in ICU it is detecting delirium in heavily-sedated and non-verbal patients.
  • Although many doctors and nurses feel they can detect delirium just from observation, it has been consistently shown that only half of all delirium is picked up without using a diagnostic instrument like the CAM-ICU
  • How good these instruments are seems to be dependent on familiarity with them
  • Another good thing about these instruments is they force people to think about delirium as a diagnosis.

-The next problem is how to deal with delirium

  • There is no good evidence for different methods to treat delirium.
  • A lot of medications like haloperidol claim to have shown an ability to treat delirium, but to my mind they haven’t really demonstrated better patient outcomes, which tells me they may just mask the outward symptoms. It also doesn’t really make any sense on a physiological level, but people tend to use it because it looks like psychosis.
  • In the majority of cases, if you can detect the acute medical change that has precipitated delirium and treat that, the delirium will resolve. So delirium should always be regarded as a marker for an acute medical change, and should warrant investigations of things like infection.
  • On the other hand, 30-40% of delirium is believed to be completely preventable, and this is to do with managing sedation targets, improving patient sleep, hydration and nutrition, reorientating patients, and correcting hearing and visual impairments.

-So delirium is a very significant condition that is not just a part of ICU care, and has a very real impact of patient care. Detection is difficult by observation alone, but can be improved by using instruments like the CAM-ICU (especially attention subtests). Delirium should prompt further investigation, but the best option is to prevent delirium before it starts by reducing precipitating factors