Acute radiation syndrome (ARS),also known as radiation poisoning,radiation sickness or radiation toxicity,is a collection of health effects which present within 24 hours of exposure to high amounts of ionizing radiation.The radiation causes cellular degradation due to damage to DNA and other key molecular structures within the cells in various tissues; this destruction,particularly as it affects ability of cells to divide normally,in turn causes the symptoms.The symptoms can begin within one or two hours and may last for several months.The terms refer to acute medical problems rather than ones that develop after a prolonged period.

The onset and type of symptoms depends on the radiation exposure.Relatively smaller doses result in gastrointestinal effects,such as nausea and vomiting,and symptoms related to falling blood counts,and predisposition to infection and bleeding.Relatively larger doses can result in neurological effects and rapid death.Treatment of acute radiation syndrome is generally supportive with blood transfusions and antibiotics,with some more aggressive treatments,such as bone marrow transfusions,being required in extreme cases.

Similar symptoms may appear months to years after exposure as chronic radiation syndrome when the dose rate is too low to cause the acute form.Radiation exposure can also increase the probability of developing some other diseases,mainly different types of cancers.These diseases are sometimes referred to as radiation sickness,but they are never included in the term acute radiation syndrome.



Signs and symptoms
Classically acute radiation syndrome is divided into three main presentations: hematopoietic,gastrointestinal and neurological/vascular.These symptoms may or may not be preceded by a prodrome.The speed of onset of symptoms is related to radiation exposure,with greater doses resulting in a shorter delay in symptom onset.These presentations presume whole-body exposure and many of them are markers which are not valid if the entire body has not been exposed.Each syndrome requires that the tissue showing the syndrome itself be exposed.The hematopoietic syndrome requires exposure of the areas of bone marrow actively forming blood elements (i.e.,the pelvis and sternum in adults).The neurovascular symptoms require exposure of the brain.The gastrointestinal syndrome is not seen if the stomach and intestines are not exposed to radiation.

1.Hematopoietic.This syndrome is marked by a drop in the number of blood cells,called aplastic anemia.This may result in infections due to a low amount of white blood cells,bleeding due to a lack of platelets,and anemia due to few red blood cells in the circulation.These changes can be detected by blood tests after receiving a whole-body acute dose as low as 0.25 Gy,though they might never be felt by the patient if the dose is below 1 Gy.Conventional trauma and burns resulting from a bomb blast are complicated by the poor wound healing caused by hematopoietic syndrome,increasing mortality.

2.Gastrointestinal.This syndrome often follows absorbed doses of 6–30 Gy (600–3000 rad).The signs and symptoms of this form of radiation injury include nausea,vomiting,loss of appetite,and abdominal pain.Vomiting in this time-frame is a marker for whole body exposures that are in the fatal range above 4 Gy.Without exotic treatment such as bone marrow transplant,death with this dose is common.The death is generally more due to infection than gastrointestinal dysfunction.

3.Neurovascular.This syndrome typically occurs at absorbed doses greater than 30 Gy (3000 rad),though it may occur at 10 Gy (1000 rad).It presents with neurological symptoms such as dizziness,headache,or decreased level of consciousness,occurring within minutes to a few hours,and with an absence of vomiting.It is invariably fatal.

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