<unk>  is an acute and relatively sudden (developing over hours to days) decline in attention-focus, perception, and cognition.<unk>  is commonly associated with a disturbance of consciousness or reduced clarity of awareness about the environment. The change in cognition including memory deficit, disorientation, language disturbance or the development of a perceptual disturbance may happen with rapid fluctuation course. The concept of<unk>  has been evolving over centuries.<unk>  was first identified in the 16th century. In the second half of the 19th century,<unk>  was identified by French workers as chaotic thinking and cognitive failure, clouding of consciousness, temporospatial disorientation. The definition of confusion and<unk>  was established by Chaslin and Bonhoeffer as the stereotyped manifestations of acute brain failure.<unk>  is classified on the basis of etiology, duration, and severity. Hyperactive<unk>  is defined as increased psychomotor activity, which may occur with increased mood lability, agitation, non cooperative attitude towards medical treatment. Hypoactive<unk>  is explained by a hypoactive level of psychomotor activity, which may exist along with increased lethargy or stupor, inattentiveness and motor slowness and is much more common among ICU admitted patients with severe disease.The exact pathophysiology of<unk>  is still being investigated.  The roles of neurotransmitters like acetylcholine and dopamine seem to be important. It involves disrupted connectivity between cortical and subcortical areas of the brain, especially areas concerned with sleep and awakening. The role of increased inflammatory cytokines has been shown in delirious  patients.<unk>  may be caused by severe physical or mental illness, or any process which interferes with the normal metabolism or function of the brain such as fever, pain, poison (toxic drug reactions), brain injury, surgery, traumatic shock, severe lack of food or water or sleep, and even withdrawal symptoms of certain drug and alcohol dependent states.  In addition, there is an interaction between acute and chronic symptoms of brain dysfunction. Delirious states are more easily produced in people already suffering from underlying chronic brain dysfunction. A very common cause of<unk>   in elderly people is a urinary tract infection, which is easily treatable with antibiotics.<unk> , like mental confusion, is a very general and nonspecific symptom of organ dysfunction. In addition to many organic causes relating to a structural defect or a metabolic problem in the brain, there are also some psychiatric causes, which may also include a component of mental or emotional stress, mental disease.Delirium is differentiated from other causes cognitive dysfunction such as  psychiatric Disorders, dementia. Unlike dementia, the course of<unk>  is reversible with fluctuation in level of consciousness.The prevalence of<unk>  is approximately 23,000 per 100,000 hospitalized patients worldwide. Between May 2009 to August 2012, the incidence of<unk>  was estimated to be 8700 cases per 100,000 African-Americans in Indianapolis.<unk>  is more commonly observed among elderly patients, especially age> 65 year-old. Male < 65 year-old are more commonly affected with<unk> .<unk>  is more commonly observed among Female≥ 85-year-old with medical comorbidities. There is no racial predilection for<unk> . Young African-American patients  are less likely to develop<unk>  compared with Caucasians of the same age.Common risk factors associated with<unk>  include older age, dementia, hypertension, emergency surgery or trauma before ICU admission, mechanical ventilation, metabolic acidosis,<unk>  on the prior day , coma.The duration of<unk>  may vary from hours to months. After remission ,<unk>  may increase the risk of functional decline, cognitive dysfunction, and institutional placement, and with higher mortality.<unk>  in the elderly, can cause many complications, which may include pneumonia and decubitus ulcers, prolonging hospital stays.<unk>  was associated with longer postoperative recovery periods, longer hospital stays, and long-term disability after orthopedic surgery. Common complications associated with<unk>  include increased mortality, cognitive impairment, longer durations of mechanical ventilation, longer lengths of stay in the ICU. Prognosis is  dependent on the severity of<unk> , and the 1 year mortality rate of patients with<unk>  is approximately 10%-26%.The DSM V, and ICD-10 have provided diagnostic criteria for<unk> . Definition based on DSM-5 include disturbance in attention and awareness (reduced ability to direct, focus, shift attention and reduced orientation to envinment), initiation of disturbance over a short period of time during several hours or days  with fluctuation  in severity over a day, disturbance in cognition (memory deficit, disorientation, language, visuospatial ability, perception, disturbance other than evolving neurocognitive disorder, disturbance due to medical condition, substance intoxication, or withdrawal. Other definitions of<unk>  include disturbance in cognition,
impairment of immediate recall and recent memory, disorientation to time, place, person, disturbance in sleep wake cycle, Psychomotor disturbances,emotional disturbances in a period of less than 6 months.Delirium causes impairment in functions, sleep-wake cycle and also has a behavioral component. Common symptoms associated with<unk>  include altered level of consciousness, inattention, disorientation, hallucination, delusions, agitation, inappropriate speech, sleep–wake disturbances, Symptom fluctuation, emotional disturbance. Subclinical<unk>  or prodromal<unk>  may precede by 1 to 3 days prior to an overt<unk> , which presents as restlessness, anxiety, irritability, distractibility, sleep disturbance with less severe cognitive impairment in comparison to<unk> .It is important to do a thorough physical examination to find out the underlying etiology of<unk> . Systemic physical examination includes testing vital signs such as temperature, pulse rate, blood pressure, and respiration and also  evaluation of mental status. Patients may seem disoriented with difficulty in  sustaining attention, problem in short-term memory, poor insight and  impaired judgment.Laboratory findings may differ according to the etiology of<unk> . Following investigations are done in<unk> : pulse oximetry, electrolytes, blood glucose, liver function tests, blood urea nitrogen, creatinine, vitamin B12 , Folate levels, measurement therapeutic drug levels, urine drug screen for substance use, blood alcohol level, complete blood count, urinalysis, thyroid function testing, erythrocyte sedimentation rate, C-reactive protein, rapid plasma reagin screening for syphilis, acquired immune deficiency syndrome/human immunodeficiency virus (AIDS/HIV) screening.Brain CT scan is helpful in the diagnosis the underlying cause of<unk> . Findings on brain CT scan among patients admitted with<unk>  include: acute or subacute infarct, haemorrhage, abscess, neoplasm, vasculitis, posterior reversible encephalopathy syndrome,  encephalitis,  acute demyelination, Fat embolism.Brain MRI is valuable tool for diagnosis  the underlying cause of<unk>  when the brain CT scan findings are not informative. The most common finding on brain MRI that was missed by  brain CT scan was ischemia.EEG maybe helpful for the diagnosis of<unk> .  EEG findings associated with<unk>  include periodic discharges, triphasic waves ,lateralized rhythmic delta ,low voltage/generalized attenuation, theta or delta generalized slowing.The presence of either theta or delta generalized slowing correlated strongly with<unk>  severity regardless of arousal state (hyper- or hypoactive) and comorbidities.Treatment of<unk>  involves two main strategies: first, treatment of the underlying presumed acute cause or causes, secondly, optimizing conditions of the brain.  This involves ensuring that the patient with<unk>  has adequate oxygenation, hydration, nutrition, and normal levels of metabolites, so that drug  effects are minimized, constipation treated, pain  treated, and so on.  Detection and management of mental stress are also very important.  Therefore, the traditional concept that the treatment of<unk>   is treating the cause is not adequate. Common medications which are used for treatment of<unk>   include antipsychotic drugs, benzodiazepines, cholinestrase inhibitors, selective -a2 receptor agonist, melatonin based medications, and  ketamine. It is important to prevent<unk>  as<unk>  is itself neurotoxic.<unk>  is associated with global brain atrophy and white matter disruption. Various non pharmacological and pharmacological interventions are found to be effective to prevent<unk> . Primary prevention sterategies for Post-operative<unk> ]] include use of haloperidol, second generation antipsychotics, iliac fascia block, lower levels of intraoperative propofol for sedation, continuous intravenous infusion of dexmedetomidine, and use of Melatonin. ketamine is not useful for prevention of postoperative<unk> . Preoperative administration of gabapentin is not effective for prevention of postoperative<unk> .Secondary prevention strategies following<unk>  include avoidance of anticholinergic drugs, attention to environmental factors (sensory input, orientation aids, reassuring human contact, routine screening for finding high risk patients, early recognition of any change or fluctuation of mental state or behaviour.
Delirium
Excited delirium
Post stroke depression
Depression 
Schizophrenia
Dementia
Psychosis
Disorganized schizophrenia