Delirium in Critical Care

 September 7

by Jonathan Downham

Delirium in Mechanically Ventilated Patients Ely et al. JAMA 2001

This is a study the aim of which was to validate the use of the CAM-ICU to assess for delirium in ICU patients.

Delirium is a disturbance of consciousness characterised by an acute onset and fluctuating course of im-paired cognitive functioning so that a patient’s ability to receive, process, store, and recall information is strikingly impaired.

In this population, cognitive impairment has been shown to affect key outcome indicators such as length of stay.

Confusion Assessment Method

There is a lack of validated instruments to reliably diagnose delirium. ICU patients were excluded from using these tools mainly because they required verbal communication.

The Confusion Assessment Method is the most widely used tool for diagnosing delirium. This tool was then adapted for use in non-verbal, mechanically ventilated patients to become the CAM-ICU and a small pilot study was carried out to help in the development of this tool.


The purpose of this study was to validate this tool, incorporate the improvements from the pilot study and to determine how often delirium affects the mechanically ventilated patient.


This was a single centre study in the US carried out from February to July 2000. Patients included were those that were mechanically ventilated and exclusions included:

  • history of psychosis or neurologic disease.
  • inability to communicate with assessors (did not speak English or were deaf)
  • admitted to ICU but extubated before study nurses assessments
  • patient or family refusal.

The final sample size was 96 patients.

Delirium, as defined by CAM has 4 features:

  1. an acute onset of changes or fluctuations in the course of mental status
  2. inattention
  3. disorganised thinking
  4. altered level of consciousness

The patient is considered delirious if they have 1 and 2 plus either of 3 or 4.

To assess for changes in mental status fluctuations in the Richmond Agitation Sedation Score (RASS) were used and the Attention Screening Examination was used to assess for inattention. Two critical care nurses enrolled patients an performed independent CAM-ICU ratings during the patients stay.

Reference standard evaluations were carried out to compare the effectiveness of the CAM-ICU using DSM-IV delirium ratings. These were carried out by a geriatrician, geriatric psychiatrist and a neuropsychologist.


With the study population of 96 patients, a total of 471 paired observations between the nurses and the delirium experts were carried out. The 2 nurses sensitivities (a highly sensitive test means that there are few false negative results, and thus fewer cases of the disease are missed. The specificity of a test is its ability to designate an individual who does not have a disease as negative. A highly specific test means that there are few false positive results) using the CAM-ICU compared with the reference standard were 100% for nurse 1 and 93.5% for nurse 2. Their specificities were 97.8%  and 100% respectively. There was also excellent interrater reliability between nurse 1 and nurse 2.

Ina sub group analysis the CAM-ICU also proved useful in those patients greater than 65 years old, with suspected dementia and the highest severity of illness.

The CAM-ICU was completed in a mean of 2 minutes.

Delirium occurred in 83.3% of patients and it was present in 40% alert or easily roused patients who were usually considered to be cognitively intact.

Delirium is often not recognised and is often considered as an expected occurrence due to an ITU psychosis.

Incorporation of the CAM-ICU into clinical practice and future investigations may lead to a more precise understanding of the incidence, predictors, and consequences of delirium among critically ill patients.


Delirium as a Predictor of Mortality in Mechanically Ventilated Patients in the Intensive Care Unit. Ely et al JAMA 2004

What is the direct contribution of delirium to clinical outcomes in critically ill ICU patients? This is the question this study tries to answer.

One of the key points the article makes is that previously delirium has received little attention in ICU settings because it is:

  1. rarely a primary reason for admission
  2. often believed to be iatrogenic due to medications
  3. frequently explained as ITU psychosis
  4. believed to have no adverse consequences in terms of patients ultimate outcome.

This study was done to test the hypothesis that delirium in the ICU is an independent predictor of 6-month mortality and length of stay among patients receiving mechanical ventilation.


A single centre study.

Patients neurologic status was assessed daily by the study nurses and defined as normal, delirious or comatose. This was done using the RASS (see above). Delirium was measured using the CAM-ICU.

Patients would be included in the “delirium” group if they ever had delirium or the “no delirium” group. they were further broken down into “delirium only” or “delirium-coma”.

Primary outcome variables included 6-month mortality, overall hospital length of stay and ICU length of stay. There were 2 secondary outcomes: ventilator free days and cognitive impairment at discharge.


224 patients were used in the final analysis. 18.3% never demonstrated delirium in the IVCU- the “no delirium” group. Delirium developed in 87.5% of patients- the “delirium” group. Delirium occurred in 77.9% of those without coma and in 83.7% of those with coma. Overall, patients spent 21.6% of their ICU days as normal, 43.1% as delirious and 35.3% as comatose.

Of the patients who were alert or easily rousable as measured by a RASS of 0 or -1, more than half were delirious.

6-month mortality – 34% 0f patients in the delirium group died versus 15% of the patients in the no delirium group. Adjusting for the covariates delirium was associated with a more than 3 times higher risk of dying by 6 months.

Each additional day that the patient spends delirious was associated with a 10% increased risk of death.

Compared with patients in the no delirium group, those who did develop delirium spend a median of 10 days longer in the hospital overall.

At any given time during the hospital stay patients diagnosed with delirium had an adjusted risk of remaining in the hospital that was twice as high as those who never developed delirium and a 60& greater risk of remaining in the wards after ICU discharge.

There were significantly fewer days alive and free of the ventilator among patients in the delirium group versus those in the no delirium group. Of those tested twice as many patients in the delirium group vs the no delirium group exhibited cognitive impairment at hospital discharge.


Risk factors for delirium:

  • preexisting cognitive impairment
  • advanced age
  • use of psychoactive drugs
  • mechanical ventilation
  • untreated pain
  • variety of medical conditions (heart failure, prolonged immobilization, abnormal blood pressure, anemia, sleep deprivation and sepsis)

Options to improve care:

  • correct brain ischemia/hypoxia
  • modify administration of psychoactive medications
  • aggressively treat sepsis especially in elderly patients.

We found that delirium among mechanically ventilated patients in the ICU was associated with higher 6-month mortality and longer lengths of stay even after adjusting for numerous covariates.


Days of Delirium are Associated with 1 Year Mortality in an Older Intensive Care Unit Population Pisani et al American Journal of Respiratory and Critical Care Medicine 2009

The aim of this study was to look at the relationship between the number of days of delirium in the older ITU group, that group being over 60 years of age.


304 patients were recruited and, as they were critically ill, consent was sought from proxies. Medical records were examined to obtain demographics.

Delirium was assessed using CAM-ICU and alertness using the RASS Monday- Friday over a space of 2 years.

A day was considered to be a delirium day if there was any episode of delirium during that day.

Main outcome variable was time of death during the ICU stay or within the first year after admission.

Other covariates included pre existing dementia, medications on ICU admission, APACHE score and whether the patient was admitted from the emergency room.


During the course of the 1 year follow up 153 patients died. The median length of ICU stay was 5 days and the median duration of delirium was 3 days.

The association between the number of days of ICU delirium and mortality was statistically significant-hazard ratio 1.10; 95% confidence interval, 1.02-1.18.

A reference is made to Schweickert’s study which showed a reduction in ICU delirium days with early mobilization and occupational therapy.

Reduction of the use of benzodiazepines is one of the ways of reducing delirium-interestingly in this American study only seven of the patients received propofol.

So mortality seems to be a greater risk in the older patient if that delirium lasts for longer. One study is quoted where 72% of the patients had delirium on their first ICU day, emphasizing the degree of the problem and there need to be increased efforts to prevent, detect and treat delirium.

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