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Acute encephalopathies are brain disorders with many different causes. They are often characterized by delirium, neuromuscular changes, and seizures. Oxygen deprivation due to cardiac arrest or brain injury can cause encephalopathy, because neurons in the central nervous system cannot do without oxygen for more than a few minutes without suffering permanent damage. Metabolic disorders trigger acute encephalopathy, which can sometimes be reversed if caught early enough, before permanent brain damage occurs.
An encephalopathy is a disorder of the brain caused by global brain dysfunction, as opposed to problems with one or two regions of the brain. Acute encephalopathy refers to the relatively sudden onset of these dysfunctions, such as when it is caused by lack of oxygen supply, toxic drugs, or metabolic disorders. Mental problems such as delirium and mood swings can arise from this condition, which can entail sudden personality changes. Encephalopathies are syndromes caused by injury or disease, but cannot in themselves be considered an illness.
One major symptom of acute encephalopathy is delirium, a transient disturbance in attention, consciousness, and cognitive capacity. If it accompanies acute and life-threatening metabolic problems, or adverse drug interactions in the body, delirium may be called metabolic or toxic encephalopathy and is often reversible if these chemical problems are treated. Further, altered mental states can accompany neurological problems like muscle twitches and erratic jerking movements or difficulties with normal breathing regulation. Delirium is a common way that encephalopathies can be identified clinically, before laboratory tests reveal the underlying chemical disturbance more definitively.
Depression of central nervous system functions can be life-threatening during encephalopathy, resulting in irreversible coma or death. Treatments often focus on relieving the underlying problems, such as correcting metabolic disorders or treating drug toxicity. Severe seizures may be treated with anticonvulsants, while respiratory assistance might be given to patients whose brains are not properly controlling respiratory and other vital functions. Sometimes conditions like asthma and anemia deprive sensitive tissue of oxygen for a long enough time to cause global brain dysfunction, but this may result in chronic and not acute encephalopathy, as it takes time for the oxygen deprivation to reach systemic levels.
Brain neurons especially require constant oxygen supply for their survival, and become damaged, often irreversibly, with anything more than a few minutes of oxygen deprivation. Hypoxic ischemic acute encephalopathy is the consequence of the brain's oxygen supply being severely diminished, even if not fully cut off. It can be caused by the heart stopping, which shuts off circulation to the brain. In newborns, it is a consequence of birth asphyxia, a condition sometimes caused by the umbilical cord being wrapped around the infant's neck. Newborns who survive hypoxic ischemic encephalopathy are still at risk of permanent brain damage due to oxygen deprivation.