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Last updated: August 6, 2020
Revisions: 23

Last updated: August 6, 2020
Revisions: 23

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Delirium is an acute confusional state, characterised by a disturbed consciousness and reduced cognitive function.

It is a common post-operative complication, occurring in around 15% of elderly patients following general surgery, yet is often still poorly identified and managed.


There are 3 main types of delirium:

  • Hypoactive delirium (most common) – marked by lethargy and reduced motor activity
  • Hyperactive delirium (most recognised) – marked by agitation and increased motor activity
  • Mixed agitation – marked by fluctuations throughout a day

Additionally, it is important to appreciate the differences between delirium and dementia, as described in Table 1.

  Delirium Dementia
Onset Acute Insidious
Short-Term Course Fluctuating Constant
Attention Poor Good
Delusions and Hallucinations Common, simple, fleeting Less common, more stable

Table 1 – Differences between delirium and dementia

Risk Factors

The major risk factors for delirium are:

  • Age >65yrs
  • Multiple co-morbidities
  • Underlying dementia
  • Renal impairment
  • Male gender
  • Sensory impairment (hearing or visual)


The common causes for delirium are:

  • Hypoxia (post-operatively)
  • Infection (commonly UTI or LRTI)
  • Drug-induced (benzodiazepines, diuretics, opioids, or steroids) or drug withdrawal (alcohol or BZNs)
  • Dehydration or pain
  • Constipation or urinary retention
  • Electrolyte abnormalities (e.g. hyponatraemia, hypernatraemia, or hypercalcaemia)


Assessing an acutely confused post-operative patient can prove a challenge, but obtaining collateral history from family members or nursing staff will normally provide key information. The key features to ascertain include:

  • Onset and course of confusion
  • Symptoms of a possible underlying cause
  • Co-morbidities and previous baseline cognition
  • Previous episodes
  • Drug history (including alcohol intake)


An Abbreviated Mental Test (AMT, Table 2) or Mini-Mental State Examination (MMSE) can quantify the current cognitive function, allowing for a comparison with any previous AMT or MMSE scores. A Confusional Assessment Method (CAM) may also be used to further quantify any delirium.

When examining a post-operative patient with confusion, it is important to review their observations, drug chart, look for any signs of infection (including any surgical site infections) or pain, and check for signs of constipation or urinary retention.

Importantly, a neurological examination should be performed to rule out any sinister underlying neurological pathology (e.g. stroke or subdural haematoma).

The Abbreviated Mental Test (AMT)
1.     Age 1
2.     Time (to nearest hour) 1
3.     Address (for recall at end of test) 1
4.     Year 1
5.     Name your home address 1
6.     Recognition of two persons/objects 1
7.     Date of birth 1
8.     Year of First/Second World War 1
9.     Name of current monarch 1
10.   Count backwards 20-1 1

Table 2 – The Abbreviated Mental Test content


Any post-operative patient presenting with confusion may warrant a ‘confusion screen’, especially if no obvious source of confusion is present following assessment, whereby the common causes of delirium are specifically investigated.

A confusion screen may include:

  • Bloods – FBC, U&Es + Ca2+, TFTs, and glucose
    • B12 and folate levels may also be additionally requested
  • Blood cultures and / or wound swabs
  • Urinalysis and/or CXR
  • CT head (only if relevant)


Any identified cause of delirium should be treated appropriately, such as antibiotics if any infection identified, nasal oxygen if hypoxic, or laxatives for any constipation.

Patients should be nursed in an appropriate environment (quiet area, regular routines, and clocks to orientate to time and place) and regular sleeping patterns promoted. Prevent worsening of any delirium by encouraging oral fluid intake, provide analgesia as necessary, and monitor bowels.

Sedatives should be used sparingly on any acutely confused patient. However, if sedatives are required, NICE guidelines recommend the use of haloperidol as 1st line treatment (try oral route initially if possible) yet lorazepam may be required, especially in elderly patients.

Key Points

  • Delirium is an acute confusional state, characterised by a disturbed consciousness and reduced cognitive function
  • There are 3 main types of delirium identified, hypoactive, hyperactive, and mixed agitation
  • Common causes for delirium post-operatively include hypoxia, infection, drug-induced, dehydration, pain, constipation, or urinary retention
  • Ensure a thorough assessment, including confusion screen investigations, and manage appropriately any suspected underlying cause