Acute radiation syndrome: An acute illness caused by a dose greater than 50 rads of penetrating radiation to most or all of the body in a short time, usually a matter of minutes. Examples of persons who suffered from acute radiation syndrome (ARS) are the survivors of the Hiroshima and Nagasaki atomic bombs and the firefighters that first responded after the Chernobyl Nuclear Power Plant event in 1986.
A person with ARS usually goes through four stages. In the prodromal stage, the classic symptoms are nausea, vomiting, and possibly diarrhea (depending on dose) that occur from minutes to days following exposure. These symptoms may last (episodically) for minutes up to several days. Then comes the latent stage. In this stage the patient looks and feels generally healthy for a few hours or even up to a few weeks. Then comes the overt or manifest illness stage, In this stage the symptoms depend on the specific ARS syndrome and last from hours up to several months. The last stage is recovery or death. Most patients who do not recover die within several months of exposure. For those who recover, the process lasts from several weeks up to two years.
The bone marrow syndrome is characterized by anorexia (lack of appetite), fever, and malaise. There is a drop in all blood cell counts for several weeks. The primary cause of death is infection and hemorrhage. The chance of survival decreases with increasing dose of radiation.
The GI syndrome is more severe. It includes severe diarrhea, fever, dehydration, and imbalance in the electrolytes (sodium, potassium, etc). Death is due to infection, dehydration and electrolyte imbalance and usually occurs within 2 weeks of exposure.
The CV/CNS syndrome is the most severe. There is initially extreme nervousness; confusion; severe nausea, vomiting, and watery diarrhea; burning sensations of the skin; and loss of consciousness. After the latent period, 5 to 6 hours after exposure there is return of watery diarrhea, convulsions, and coma and death comes within 3 days of exposure.