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Acute Radiation Sickness

Overview of biologic effects of radiation, acute radiation sickness

Biological effects of radiation are dependent upon the type of exposure a person has with the duration of the exposure and intensity of the material playing a key role. We also have to include the role of personal protection such as time, distance and shielding.

Acute Radiation Sickness (sometimes called Acute Radiation Syndrome or ARS), occurs when an individual is exposed to a large amount of radiation in a short period time or a total doses greater than 100 REM (100 RAD  for gamma radiation).  Acute radiation sickness has a variety of clinical features; some are obvious, some not.In general, the clinical manifestations of acute radiation sickness include the following:
  • changes in blood cell count, specifically lymphocytes decrease
  • vascular permeability changes
  • gastrointestinal irritation; nausea, vomiting, and diarrhea
  • fever
  • hair loss, in uneven patterns
  • skin rash, skin burns, in general skin irritation
  • vague symptoms such as flu-like symptoms
The appearance of these symptoms may begin within minutes after exposure or may not appear for several days. Symptoms may disappear after a few days and resurface with severe illness. Individual unique response to radiation is variable that has to be accounted for as well as age and pre-existing medical condition.

Acute radiation sickness has four phases and may manifest with four separate syndromes.
The four syndromes of acute radiation sickness  are:
  • Hematopoietic Syndrome
  • gastrointestinal syndrome
  • cardiovascular syndrome
  • and central nervous system syndrome
The four phases of acute radiation sickness are:
  • prodromal phase
  • latent phase
  • manifest phase (sometimes called the period of illness)
  • and recovery or death
From: REMM
 Hematopoietic Syndrome  effect the blood cells and platelet counts. The lymphocyte count begins to drop and is seen is the earliest marker or indicator of the degree of severity of exposure and subsequent acute radiation sickness.  Complications associated with Hematopoietic Syndrome  including infection and internal hemorrhage. Changes in lymphocyte counts are detected or measured on a Andrews Curve. The Andrews curve graphs the lymphocyte count for the first 48 hours. In addition to being a marker for severity of exposure to radiation,  decreasing lymphocytes are also all marker for treatment and prognosis. In many cases red blood cells and red blood cell production remains fairly normal after radiation exposure. Neutrophils decline in a gradual rate, while platelets may decrease slightly over time. Again, lymphocytes and lymphocyte counts are critical for determining the degree of severity of acute radiation sickness.

Gastrointestinal syndrome is a condition in which the epithelial lining of the G.I. system is gradually destroyed. Epithelial cells decline in results in nausea, vomiting, diarrhea, and sepsis. Sepsis is a result  of the loss of protective barrier that separates normal bacteria from the bloodstream. Gastrointestinal syndrome may impact the lower G.I. or upper G.I. tract, or both. In the lower G.I. system bloody diarrhea (frank in nature) is most common.

Large doses of whole body radiation can cause Central Nervous System and Cardiovascular syndrome. Both are caused by a destruction of blood vessels and an increase in capillary permeability. Symptoms usually appear fairly rapidly and take the form of cerebral edema, pulmonary edema, cardiogenic shock, and death. Victims exposed to large amounts of whole body radiation may often die within 72 to 80 hours, often before the symptoms of G.I. syndrome or hematopoietic  develop.

Acute radiation sickness may present within four distinct stages: prodromal, latent, manifest, and recovery/death. In the prodromal phase (approximately 48 hours after exposure) victims may present with:
  • nausea and vomiting, diarrhea
  • fatigue and headache
  • fluid shifts due to  increased permeability and electrolyte losses
 In the latent phase the victim may show signs of improvement. Depending upon the unique variables of the person and the dose/rate/body surface area of exposure. Symptoms may return in 24 hours to several days with greater severity.  The manifest illness stage produces compromise to the immune system and can present with symptoms of any one or all of the syndromes  (hematopooietic, GI, CV/CNS) discussed earlier. Symptoms may also be seen in major organ systems; particularly in the integument, neurovascular and G.I. systems of the body. The final stage of acute radiation sickness is the recovery or death stage. Unfortunately, treatment at this point is supportive in nature and the outcome is determined by the dose of radiation exposure and the body surface area along with the other variables we discussed. It should be noted that after a lethal dose of radiation, victims may progress through each of the four phases rapidly with a quick decline in status.

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