Decreased ability to direct, focus, sustain of shift attention and reduced awareness
Develops over hours or a few days and usually fluctuates in severity within hours
Disturbance in cognition–memory, disorientation, language or perception
Not due to other pre-existing or evolving neurocognitive disorder, not in coma
Evidence of cause, i.e. medical, drug overdose or withdrawal, toxin or multiple aetiologies
Delirium is an acute fluctuating brain dysfunction, which enables it to be distinguished from dementia. Patients with apparent normal cognitive function, through the course of a day, an hour or even a conversation, ramble or become paranoid and deluded. Although hallucinations are common in critically ill patients, they are not required to make a diagnosis of delirium.
2.3 Delirium Motoric Subtypes
Arousal and psychomotor activity changes account for the three clinical descriptive forms of delirium: ‘hyperactive’, ‘hypoactive’ and ‘mixed’ [4]. A patient with hyperactive delirium is easy to recognise, restless, paranoid and never ever seems to sleep. Pure hyperactive delirium, while memorable, is actually uncommon compared with the other two forms, occurring only in 5 % of cases [5]. Most delirious patients in critical care develop hypoactive delirium and generally appear lethargic, compliant and immobile. It is only by interacting with the patient that it can be appreciated they are inattentive and disorientated. With the mixed type of delirium, a patient’s behaviour fluctuates, often hypoactive during the day, but increasingly restless, often agitated overnight. Subsyndromal delirium describes a patient who has one or more symptoms of delirium, but does not meet the criteria for delirium diagnosis and does not progress to it [6].
2.4 Size of the Problem
At any one time, an acute hospital with 1000 beds would have around 100 patients with delirium. Delirium affects an estimated 18–35 % of hospitalised elderly, and its incidence in the Intensive Care Unit (ICU) has been documented as up to 82 % [7]. In critically ill patients, it prolongs length of hospital stay by up to 10 extra days, increases the likelihood of discharge to an institution and is a predictor of death [8]. In patients who require mechanical ventilation, those affected by delirium are three times more likely to die by 6 months, and the risk of dying is increased the longer time a patient is delirious [7].
In those patients who survive a critical illness, and developed delirium during the ICU stay, regardless of age, the risk of long-term cognitive impairment following discharge is increased nine times, and it is three times more likely to persist after discharge [9, 10]. This can be equivalent to mild Alzheimer’s disease. Patients’ quality of life and independence are consequently reduced with high detrimental impact on carers and families, financially and emotionally.
2.5 Risk Factors
Whether or not a patient develops delirium will depend on the risk factors (Table 2.2).
Table 2.2
Risk factors for delirium in ICU
ICU delirium-modifiable risk factors | Non-modifiable risk factors | |
---|---|---|
Infection | Hyponatraemia | Age, especially over 65 |
Anticholinergic drugs | Sedative drugs | Cognitive impairment |
Opiates | Hypoxia | Dementia |
Pain | Hypercarbia | Depression |
Immobility | Acidosis | Genetic factors |
Dehydration or Constipation | Polypharmacy | Institutionalised residence |
Use of physical restraints | Sleep disturbance | |
Sensory impairment (visual/auditory) | Use of bladder catheter |
Predisposing factors are those that make a patient more vulnerable to developing delirium following what may be only a relatively mild trigger. They are present on admission and are rarely modifiable: age, history of cognitive impairment, previous episodes of delirium, alcohol abuse, hypertension, age, liver impairment and other chronic medical conditions [11]. The precipitating cause of ICU delirium may be potentially treatable: often an infection or an episode of sepsis, electrolyte imbalance, renal failure, hypercarbia or the use of deliriogenic drugs. Non-modifiable causes would include stroke, traumatic brain injury and pancreatitis. Aggravating risk factors include the use of a bladder catheter, uncontrolled pain, hypnotic and narcotic drugs, visual or hearing impairment and immobility [12]. PRE-DELIRIC is a validated delirium risk prediction score for ICU patients derived from data collected during the first 24 h and is freely available for use [13].
2.6 Routine Monitoring of Delirium
Monitoring delirium is an essential part of routine daily assessment. Ongoing delirium and new delirium is a significant clinical sign. Several studies have demonstrated that clinicians regularly miss delirium in the ICU settings [14]. Most critically ill patients will develop hypoactive delirium, but will be able to obey direct commands, e.g. stick your tongue out, squeeze my hand and usually answer yes to most questions, e.g. do you feel better this morning? In order to detect delirium in critically ill patients, whether intubated or not, clinicians need to use a screening tool or have a meaningful exchange. Routine screening for of all acutely ill hospital patients has been recommended by the National Institute for Health and Care Excellence (NICE) and the Pain, Agitation and Delirium (PAD) guidelines from the American College of Critical Care [15, 16]
Currently, there are two non-verbal screening tools for use in intubated patients, and both are recommended in the PAD guidelines: the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) and the Intensive Care Delirium Screening Checklist (ICDSC) [17, 18]. They were developed for clinical use and have been validated against the standard DSM-4 criteria. Both tools can be used in sedated intubated patients for the assessment of delirium; however, patients must be responsive, i.e. able to open their eyes and keep them open in response to a verbal stimulus, usually their name. They require training and practice.
The CAM-ICU is a point in time assessment usually completed twice a shift or when the nurse detects a change in mental status, while the ICDSC is completed during the course of a shift on observing patient behaviour. It is worth specifying that low-arousal states of acute onset with a severely withdrawn patient who does not interact should be recognised as likely indicating delirium.
2.6.1 Confusion Assessment Method for the Intensive Care Unit (CAM-ICU)
CAM-ICU (Fig. 2.1) is a modified version of the original CAM screening instrument completed in up to four steps, taking on average 2 min [19]. It assesses four core components of delirium: altered or fluctuating mental status, inattention, disorganised thinking and altered level of consciousness. Before starting, the patient’s level of arousal is established using a sedation score such as the Richmond Agitation Sedation Score (RASS) [20].
Fig. 2.1
Confusion Assessment Method for ICU (CAM-ICU) flow chart (Copyright © 2002, E. Wesley Ely, MD, MPH and Vanderbilt University. All rights reserved)
Step 1. Has there been acute onset of change in mental status? On admission, ask patient’s relatives if necessary – ‘is your relative/partner/friend behaving normally?’ Has there been a change from the patient’s mental status baseline and/or has there been any fluctuation over the past 24 h?
Step 2. Look for inattention. Is the patient able to pay attention long enough to squeeze the clinician’s hand on the ‘A’s in a 10-letter sequence, such as SAVE A HAART, or A BAD BAD DAY?
Patients who are able to squeeze the assessor’s hand correctly on the ‘A’s and not on other letters with no more than two mistakes are negative for delirium, using the CAM-ICU.
Continue only in patients with more than two mistakes on the attention screen:
Step 3. Is the patient drowsy? Or hyperalert?
Patients who fail the attention screen and are drowsy or hyperalert are CAM-ICU-positive.
Continue in patients who have normal conscious level (step 3 negative).
Step 4. Look for disorganised thinking. Ask the patient four ‘yes or no’ questions from a choice of two sets provided in the tool and then ask him/her to follow a simple command.
Patients who fail the attention screen and have more than one error in step 4 are CAM-ICU-positive.
In summary, a patient is screened as positive for delirium at that point in time if they have an altered mental status and are inattentive and show either disorganised thinking or an altered level of consciousness.
2.6.2 Intensive Care Delirium Screening Checklist (ICSDC)
The ICDSC is a checklist of eight items recorded over a period of time, usually a nursing shift [18].
Each item is a common feature of delirium:
Level of consciousness (only scores in patients not on sedation)
Inattention (is the patient easily distracted or repeating words/actions? Not thought to be due to sedative drugs)
Disorientation (time and place)
Hallucination/delusion/psychosis
Psychomotor agitation or retardation
Inappropriate speech or mood
Sleep/wake disturbance (too sleepy or never sleeps)
Fluctuation of symptoms
One point is allocated if the nurse detects an item from the list at any time during the course of the observation period. If the patient scores four or more points, he/she is considered to have delirium. If they score one to three, they have subsyndromal delirium. For the ICSDC, the information is readily available, although detecting it relies on subjective interpretation by the observer.
2.6.3 Sedated and Non-intubated Patients
There are a small percentage of intubated patients who will screen positive using the CAM-ICU while on sedation, but following a 2-h sedation hold will screen negative. Early results would suggest that patients with this ‘rapidly reversible sedation-induced’ delirium appear to have the same clinical outcomes with regard to the length of ventilation and stay in ICU as those who do not screen positive at all [21]. Units using the CAM-ICU may consider additional screening during sedation breaks.
Paradoxically, the CAM-ICU and ICDSC are both highly specific, but lack sensitivity in non-intubated acutely ill patients, i.e. a patient may have delirium, but screen negative [22]. To increase the detection of delirium, use a simple additional test: ask the patient to tell you the months of the years going backwards [23]. If the patient does not engage or cannot complete up to seven months backwards, then that would indicate ongoing delirium [24].
2.7 Managing Delirium in the ICU
New delirium is an important early sign of clinical deterioration; it often precedes other indicators and can enable early intervention.
2.7.1 Treat the Cause
The key to manage delirium lies in establishing and treating the underlying cause(s), whatever is maintaining or has precipitated delirium. In ICU, the common causes are drugs and/or infections. In PRE-DELIRIC, a delirium prediction model for ICU patients, the highest scoring risk factors are coma from any cause, sedatives and infection [14]. Useful checklists include THINK or I WATCH DEATH mnemonics that help with establishing potential causes in individual patients (Table 2.3) [25].
Table 2.3
Two examples of delirium risk factors mnemonics
THINK | I WATCH DEATH |
---|---|
Toxic situations Reversal and aggressive treatment of underlying cause(s) such as CHF and shock Stopping unnecessary deliriogenic agents that may be impairing brain function | Infection: HIV, sepsis, pneumonia |
Hypoxemia, or consider giving haloperidol or other antipsychotics | Withdrawal: alcohol, barbiturate, sedative-hypnotic |
Infection/sepsis, or Immobilisation | Acute metabolic: acidosis, alkalosis, electrolyte disturbance, hepatic failure, renal failure |
Non-pharmacological interventions, such as eyeglasses, hearing aids, reorientation and sleep hygiene | Trauma: closed head injury, heat stroke, post-operative, severe burns |
K+ medical management other than new drugs (e.g. correction of electrolyte disorders) | CNS pathology: abscess, haemorrhage, hydrocephalus, subdural haematoma, infection, seizures, stroke, tumours, metastases, vasculitis, encephalitis, meningitis, syphilis |
Hypoxia: anaemia, carbon monoxide poisoning, hypotension, pulmonary or cardiac failure | |
Deficiencies: vitamin B12, folate, niacin, thiamine | |
Endocrinopathies: hyper/hypoadrenocorticism, hyper/hypoglycaemia, myxoedema, hyperparathyroidism | |
Acute vascular: hypertensive encephalopathy, stroke, arrhythmia, shock | |
Toxins or drugs: prescription drugs, illicit drugs, pesticides, solvents | |
Heavy metals: Lead, manganese, mercury |
2.7.2 Non-pharmacological management
Non-pharmacological measures remain the only ones that have been shown to modify delirium and are therefore important to implement [26]. They relate to the unit environment, daily nursing practice and those relevant to the individual patients.