||Nausea and vomiting
|Time of onset
|Time of onset
|Time of onset
|Time of onset
||Cognitive impairment 6–20 h
||Cognitive impairment <20 h
Dizziness and disorientationHypotension;
Vomiting; Severe diarrhea;
||Mortality without medical care
||Mortality with medical care
Japanese authorities are trying to prevent total meltdown at three nuclear reactors that were damaged in Friday’s tsunami. Engineers are flooding the reactors to cool them down, then venting the radioactive steam to prevent a dangerous build-up in pressure. Thousands have been evacuated, and helicopters have detected radioactive particles 60 miles from the reactors. How can the evacuees tell if they’ve been exposed to dangerous levels of radiation?
With a blood test. Nuclear plant workers, radiologists, and rescue workers can wear badges or special rings that tell them how much radiation is in their environment. Post hoc measurement is tougher, though. Public health workers may pass a device over the patient’s clothing. The air enters an oxygen- or argon-filled chamber, and the machine detects reactions between the gas and radioactive particles. Another option is to take a swab of the patient’s nose and mouth and perform a similar experiment. If either of these methods uncover radiation exposure, doctors then draw blood. Absorption of more than 500 millisieverts of radiation can depress white blood cell levels.
At this time, it doesn’t look like anyone in Japan has taken in this much radiation. The highest reported absorption so far is just 106 msv. To put that into perspective, workers at the Chernobyl plant absorbed more than 5,000 msv, and those were the survivors. Even 500 msv is fairly benign. White blood cell counts typically rebound within a couple of days, and the patient’s increased lifetime risk of cancer is barely worth mentioning. The average American has a one-in-two chance of developing some form of cancer. One-time exposure to 500 msv raises those odds to about one-in-1.9999.
On the off chance that an unfortunate nuclear plant worker shows signs of significant radiation exposure, treatment would depend on the type of radioactive particle involved. Radioactive cesium can be treated with a chelating agent, a chemical that binds to the particle and ushers it out of the body via urine. Those who inhale a dose of radioactive iodine aren’t as lucky. While it can be treated prophylactically with potassium iodide tablets, there’s no effective remedy after the exposure. The victim has to wait for his body to process the contaminant.
Radiation Exposure Monitoring (REM) facilitates the collection and distribution of information about estimated patient radiation exposure resulting from imaging procedures.
Radiation poisoning, radiation sickness or a creeping dose, is a form of damage to organ tissue caused by excessive exposure to ionizing radiation. The term is generally used to refer toacute problems caused by a large dosage of radiation in a short period, though this also has occurred with long term exposure. The clinical name for radiation sickness is acute radiation syndrome (ARS) as described by the CDC. A chronic radiation syndrome does exist but is very uncommon; this has been observed among workers in early radium source production sites and in the early days of the Soviet nuclear program. A short exposure can result in acute radiation syndrome; chronic radiation syndrome requires a prolonged high level of exposure.
Radiation exposure can also increase the probability of developing some other diseases, mainlycancer, tumours, and genetic damage. These are referred to as the stochastic effects of radiation, and are not included in the term radiation sickness.
The use of radionuclides in science and industry is strictly regulated in most countries. In the event of an accidental or deliberate release of radioactive material, either evacuation or sheltering in place are the recommended measures. For information on the effects of lower doses of radiation, see the article on radiation orders of magnitude.
A gray (Gy) is a unit of radiation dose absorbed by matter. To gauge biological effects the dose is multiplied by a ‘quality factor’ which is dependent on the type of ionising radiation. Such measurement of biological effect is called “dose equivalent” and is measured in sievert (Sv). For electron and photon radiation (e.g. gamma), 1 Gy = 1 Sv.
The corresponding non-SI units are the rad (radiation absorbed dose; 1 rad = 0.01 Gy), and rem (roentgen equivalent mammal/man;1 rem=0.01 Sv).
Annual limit on intake (ALI) is the derived limit for the amount of radioactive material taken into the body of an adult worker by inhalation or ingestion in a year. ALI is the intake of a given radionuclide in a year that would result in:
- a committed effective dose equivalent of 0.05 Sv (5 rems) for a “reference human body”, or
- a committed dose equivalent of 0.5 Sv (50 rems) to any individual organ or tissue,
whatever dose is the smaller.[9
Signs and symptoms
Radiation sickness is generally associated with acute (a single large) exposure. Nausea and vomiting are usually the main symptoms.The amount of time between exposure to radiation and the onset of the initial symptoms may be an indicator of how much radiation was absorbed, as symptoms appear sooner with higher doses of exposure. The symptoms of radiation sickness become more serious (and the chance of survival decreases) as the dosage of radiation increases. A few symptom-free days may pass between the appearance of the initial symptoms and the onset of symptoms of more severe illness associated with higher doses of radiation. Nausea and vomiting generally occur within 24–48 hours after exposure to mild (1–2 Sv) doses of radiation. Radiation damage to the intestinal tract lining will cause nausea, bloody vomiting and diarrhea. This occurs when the victim’s exposure is 200 rems (1 Sv = 100 rems) or more. The radiation will begin to destroy the cells in the body that divide rapidly, including blood, GI tract, reproductive and hair cells, and harm the DNA and RNA of surviving cells. A direct quantitative relationship exists between the degree of the neutropenia that develops after exposure to radiation and the increased risk of developing systemic infection (sepsis). Headache, fatigue, and weakness are also seen with mild exposure. Moderate (2–3.5 Sv of radiation) exposure is associated with nausea and vomiting beginning within 12–24 hours after exposure. In addition to the symptoms of mild exposure, fever, hair loss, infections, bloody vomit and stools, and poor wound healing are seen with moderate exposure. Nausea and vomiting occur in less than 1 hour after exposure to severe (3.5–5.5 Sv) doses of radiation, followed by diarrhea and high fever in addition to the symptoms of lower levels of exposure. Very severe (5.5–8 Sv of radiation) exposure is followed by the onset of nausea and vomiting in less than 30 minutes followed by the appearance of dizziness, disorientation, and low blood pressure in addition to the symptoms of lower levels of exposure. Severe exposure is fatal about 50% of the time. Severe sepsis is the cause of death in most cases. See criticality accident for a number of incidents in which humans have been accidentally exposed to such levels of radiation.
Longer term exposure to radiation, at doses less than that which produces serious radiation sickness, can induce cancer as cell-cycle genes are mutated. The probability cancer will develop is a function of radiation dose. In radiation-induced cancer the disease, the speed at which the condition advances, the prognosis, the degree of pain, and every other feature of the disease are not functions of the radiation dose to which the person is exposed.
Since tumors grow by abnormally rapid cell division, the ability of radiation to disturb cell division is also used to treat cancer (seeradiotherapy), and low levels of ionizing radiation have been claimed to lower one’s risk of cancer (see hormesis).
Organisms causing sepsis
The systemic infections can be endogenous originating from the oral and gastrointestinal bacterial flora, and exogenous originating from a breached skin and environment following trauma.
The organisms causing endogenous infections are generally Gram negative bacilli such as Enterobacteriacae (i.e. Escherichia coli, Klebsiella pneumoniae, Proteus spp.), Pseudomonas aeruginosa, and Enterococcus spp. (of gastrointestinal origin) and Streptococcus spp. (of oral cavity source).
Exposure to higher doses of radiation is often associated with anaerobic infections due to Gram negative bacilli and gram positive cocci. Fungal infections can also emerge in those who fail antimicrobials and are still febrile for over 7-10 days.
Exogenous infections can be caused by organisms that colonize the skin such as Staphylococcus aureus or Streptococcus spp. and organisms that are acquired from the environment such as Pseudomonas spp.