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Delirium is a disorder characterized by disturbances in consciousness, orientation, memory, thought, perception and behavior of acute onset and fluctuating course. Many with pre -existing dementia and appears to be independently associated with significant increase in functional disability, length of hospital stays, rates of admission to long term care institutions rate of death and healthcare cost. Despite its clinical importance delirium is often not detected or misdiagnosed as dementia or other psychiatric illness.

       Symptoms of the delirium develops over hours to days, although onset may be abrupt. Clouding of consciousness is cardinal feature of the delirium. There is reduced ability to focus, sustain or shift attention to external stimuli that may account for all other cognitive deficits. distractibility and decreased concentration follow from inability to focus or sustain attention. Abnormalities in the form and content of thinking are prominent. The organization and utilization of information are impaired. thinking may become illogical. Language functions are often abnormal. Speech may be tangential, circumstantial poorly organized, slow and slurred speech, word finding difficulties. There is disturbance in remote and recent memory. disorientation is most commonly manifested by mistakes in time, place and sometime person.

  Perceptual disturbances can occur like illusion or hallucination. visual, auditory are more common.  Psychomotor disturbances can occur.  In hyperactive delirium characterized by agitation, autonomic arousal, diaphoresis, tachycardia, dilated pupil, dry mouth.

   Delirium is a multifactorial in older patients. The multifactorial model for the etiology of delirium has been well validated and widely accepted. The development of delirium involves exposure to noxious insults or precipitating factors.

Neuroinflammation is one possible pathophysiological mechanism for post operative delirium. Systemic inflammatory mediators are significantly increased after surgery and remain high in post operative period. preclinical studies have shown that peripheral inflammation can lead to loss of structural and functional loss of blood brain barrier integrity, subsequently leading to translocation of inflammatory mediators and cells into CNS. This finally leads to loss of neuroplasticity.

It is reported that diseases that increase the risk of cerebrovascular events such as hypertension, atrial fibrillation and previous stroke are all risk factors for developing the post op delirium. radiological evidence cerebral ischemia can be seen in 7-10 percent of the elderly post -surgical patient and this associated with more than double the risk of post operative delirium. small cohort study of lung transplant patient showed that every 10 mm hg decrease in cerebral perfusion pressure is associated with double risk of post operative delirium.

  Polypharmacy is commonly associated with the advanced age and presence of multiple comorbidities both of which increases the post operative delirium. Polypharmacy itself is the independent risk factor for the development of the delirium in older population.  large number of medications are thought to directly increase the risk of delirium.

 prolonged fasting result in unnecessary use of the iv fluid and other perioperative complication such as nausea and vomiting.  A large cohort study found that fluid fasting more than 6 hours is the independent risk factor for the development of post operative delirium. Several observational studies have found that preoperative pain is associated with 1.5 to 3 times higher risk of postoperative delirium. Pain triggers acute stress response and increases the other post operative complication which may cause delirium. Surgical trauma can cause acute stress response and systemic inflammation. In additions higher incident of the postoperative delirium are mostly reported in association with the complex surgeries.

Predisposing factors for delirium

1.    Reduced cognitive reserve: dementia, depression, advanced age. Reduced physical reserve: atherosclerotic diseases, renal impairment, advanced age, preoperative beta blockade, alcohol abuse, malnutrition, dehydration, apolipoprotein e4 genotype

Precipitating factors for delirium

Medication or medication  withdrawal: Anticholinergics, muscle relaxant, antihistamines,  GI antispasmodics, opioid analgesics, Antiarrhythmic, corticosteroids, greater 6 total medication, greater than 3 new inpatient medication .hypoxemia, electrolyte abnormalities, malnutrition, dehydration, environmental changes such as  ICU admission ,Sleep wake cycle disturbance, urinary catheter use, restraint use, psychotropic medication use: antidepressant, antiepileptics, antipsychotics, benzodiazepines.                                                 

As it is increasingly evident that delirium is associated with poor outcome and increase health care costs, its timely diagnosis is crucial to prevent patients from developing severe long -lasting complications. Only a fraction of patient with delirium are quickly recognized by the caregivers. Those   patients usually present with hyperactive forms of the delirium commonly characterized by the agitation, restlessness, hallucination and delusion, In contrast the hypoactive form of delirium characterized by reduced    movements, paucity of speech and unresponsiveness can be misdiagnosed as the depression, anxiety or a calm and comfortable patient when proper screening is not performed. A rough distribution of the delirium presentation suggest that it may be of hyperactive forms percent hypoactive form percent, and mixed form 25 percent of cases. The more clinically silent hypoactive type may be associated with higher mortality that hyperactive types.

      As missing the diagnosis of delirium might have important negative consequences on outcome, clinicians should actively look for it; especially in high- risk patients, Screening must be performed in all vulnerable patients to minimize the impact of these conditions.

      In diagnosing delirium there are no definitive laboratory tests, and the differential diagnosis for acute abnormalities of cognition and attention are broad. A complete blood count, electrolyte panel, glucose measurement, arterial blood gas, urine analysis and electrocardiography should be considered in all patients with acute confusion to rule out correctable conditions like hypoxemia, hypoglycemia, and electrolyte imbalance .Life threatening organic condition like withdrawal syndromes [e.g. ethanol] and intracranial condition like meningitis, hypertensive crisis and status epilepticus should be given appropriate consideration. Imaging studies like chest radiography, computed tomography, or magnetic resonance imaging of head should be requested on the basis of clinical suspicion of specific pathologies such as stroke. Electroencephalography may show non -specific changes, particularly generalized slowing to theta delta range.