High dose of penetrating radiation exposure over a short period of time (usually within minutes) causes depletion of immature parenchymal cells in certain tissues leading to Acute Radiation Syndrome (ARS). In this case, the dose of penetrating radiation is usually, 0.7 Gray (Gy) or 70 rads. Here, Gy is unit of absorbed dose showing an amount of energy (joule) deposited into a mass of tissue (kg).
ARS is also referred to as Radiation toxicity / Radiation sickness. There are three ARS syndromes, including Hematopoietic / Bone marrow syndrome (>0.7 Gy), Gastrointestinal (GI) syndrome (>10 Gy), and Cardiovascular (CV) / Central Nervous System (CNS) syndrome (>50 Gy).
There are four stages of ARS, including prodromal stage (N-V-D stage), latent stage, manifest illness stage, and recovery or death. prodromal stage (N-V-D stage) may last for minutes to several days, and symptoms in this stage include nausea, vomiting, anorexia, and diarrhea. Latent stage may last for few hours to few weeks, and the symptoms in this stage may include no symptoms / patient seems healthy. Manifest illness stage may last for few hours to several months, and the symptoms may vary among specific syndromes:
Hematopoietic: anorexia, fever, malaise
GI: malaise, anorexia, severe diarrhea, dehydration
CV/CNS: watery diarrhea, convulsions, coma
The stage of recovery or death may take from several weeks to two years.
CDC – https://www.cdc.gov/nceh/radiation/emergencies/arsphysicianfactsheet.htm#:~:text=Acute%20Radiation%20Syndrome%20(ARS)%20(,usually%20a%20matter%20of%20minutes).
Medical Management of Radiation Accidents *
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