04/24/2011 11:49:00 AM EST
The Last Samurai - Fukushima Daiichi Nuclear Plant Workers Sacrifice Their Lives: An Occupational Medicine Overview of Radiation Exposure and Acute Radiation Syndrome
Robin E. Kobayashi
Physicist Michio Kaku has been outspoken about the Fukushima Daiichi Nuclear Plant disaster. Recently on Real Time with Bill Maher, he said “If we keep on releasing radiation into the atmosphere, I say, call out the military and just bury the sucker”, entombing it in tons of cement. Kaku compared the Japanese workers at the Fukushima plant to samurai in that they have accepted this suicide mission to sacrifice their lives for their country. Some of the workers say they expect to die within weeks or months. What exactly will these workers experience in terms of radiation exposure? The following medical information was excerpted from Occupational Injuries and Illnesses (LexisNexis).
Radiation Sickness: An Overview of Acute Radiation Syndrome
Most deaths following radiation exposure are due to the radiation-induced illness known as acute radiation syndrome (ARS). ARS usually occurs following external whole-body irradiation. The course of ARS is affected adversely by age, impaired health and nutritional status, concomitant illness or injury, especially infection, and other factors. ARS is not a single syndrome but composed of three or four sequential subsyndromes, dominated by hematologic, gastrointestinal or cardiovascular and central nervous system symptoms, with one subsyndrome blending into another as cell death and tissue depletion are expressed.
Measurement of Dose and Exposure
A variety of instruments can detect and measure radiation reliably and accurately. Radiation detection instruments measure the number of ion pairs that are formed as radiation is absorbed by air or solid matter. The traditional terms rad (radiation absorbed dose) and rem (roentgen equivalent man), used to measure and express the dose of radiation received by body tissue, have been largely replaced in the scientific literature by the terms gray (Gy) and sievert (Sv). The units used to express doses of ionizing radiation are complicated, because the two systems are currently being used interchangeably. The so-called “special units” (rad, rem) are still used in the United States, but the SI (Systeme International) system using gray and sievert is preferred internationally.
Clinical Effects of External Radiation
External exposure from radiation sources located outside the body may also involve contamination of the skin with radioactive material and internal deposition of radionuclides. Mixed exposures can occur when the integrity of a sealed radioactive source or equipment containing radioactive materials is broken. The radiation doses from the two types of exposure are additive. The onset of symptoms usually begins with a prodromal (symptoms indicating onset of disease) phase of nausea and vomiting, which can begin within minutes to hours of exposure. It subsides over a few hours.
The median lethal dose for humans is estimated to be about 4.5 Gy if victims are hospitalized and receive supportive care. Doses in excess of 20 Gy produce central nervous system (CNS) symptoms that occur immediately after exposure and include headache, mental status aberration, prostration, vertigo, tinnitus (ringing in the ears), and sensory and motor changes. If the individual has been exposed to a nonuniform dose and the gastrointestinal and hematopoietic systems have been spared, there is a chance for recovery after resolution of the CNS symptoms. However, if more than 20 Gy of whole-body exposure occurs, fulminating gastrointestinal and CNS symptoms will ensue, and in all instances, the outcome is fatal. With whole-body exposure of more than 10 Gy, fatality is still nearly 100 percent unless bone marrow transplantation is performed. Death comes from hematopoietic system complications if the patient survives CNS and gastrointestinal system involvement.
Hematopoietic Syndrome
In doses from 1 to 5 Gy, the hematopoietic syndrome occurs as all blood stem cells—particularly lymphocyte and granulocyte precursors as well as thrombocyte and red blood cell precursors—are depleted owing to radiation-induced cell death. The main effect is pancytopenia (simultaneous decrease in the number of red cells, white cells and platelets) leading to death from sepsis aggravated by hemorrhage. Because of the white blood cell depletion, there is immune system dysfunction and decreased ability to fight infection. Recovery may take months or years, but generally, with modern treatment methods, most persons in this dose range survive, barring other complicating factors.
The absolute lymphocyte count 48 hours after exposure is a good predictor of hematopoietic involvement. If the absolute lymphocyte count is greater than 1,200, it is unlikely that the patient has received a fatal dose of radiation. If the absolute lymphocyte count falls to between 300 and 1,200 at 48 hours, the possibility of exposure to a lethal dose of radiation should be suspected.
Gastrointestinal Syndrome
The gastrointestinal syndrome is considered to occur at exposures between 6 and 30 Gy. Although the gastrointestinal stem cells are targeted for radiation, the lymphocytes are also affected. As the crypt cells are destroyed, the mucosal lining of the intestinal microvilli, which is normally shed every three to five days, is sloughed. Microvilli shorten, mucosal integrity is compromised, pooling of the microvasculature into cisternae occurs, and severe mucosal hemorrhage, exudation and ulceration result. In addition, hypersecretion of cellular fluids into the lumen occurs, which can result in fluid and electrolyte imbalances. Paralytic ileus occurs. Absorption of nutrients is impaired. With the disruption of the mucosal barriers, bacterial translocation of pathogenic aerobes and anaerobes increases; colonization of the liver occurs, and the risk of sepsis is greatly enhanced.
Absorbed radiation doses between 6 and 20 Gy are fatal even if gastrointestinal lesions heal, because bone marrow exposure is lethal. Death usually occurs from 3 to 21 days following exposure.
Cardiovascular /Central Nervous System (CNS) Syndrome
Cardiovascular/CNS syndrome is characterized by deteriorating consciousness, respiratory depression and increased vascular permeability. The prodromal symptoms are followed by ataxia (inability to coordinate voluntary muscles), prostration, sweating and shock. Extremely large doses of radiation result in rapid death due to general cardiovascular and neurologic dysfunction. Absorbed radiation doses of more than 2 Gy are rapidly and inevitably fatal within 24 to 48 hours.
Skin Burns
Radiation skin burns may occur from direct contact with a high-level radioactive source or exposure to an intense field or beam of x-rays, gamma rays, neutrons or electrons. Exposure to such high sources is not always immediately recognized; suspicion of radiation must be high if burn like pain or a skin burn is present without a known accident or event.
Development of radiation burns can occur at a much slower rate (days) than thermal burns. Clinical signs of acute radiation burn are erythema (first-degree), transepidermal injury (second-degree) and full-thickness burns (third-degree). Erythema, which is often difficult to identify in the first week, becomes more prominent in the second week. Skin response to irradiation varies according to the type and energy of the radiation as well as to amount of surface area irradiated.
Diagnosis
The person who is accidentally and highly exposed to ionizing radiation is often aware—or suspects—that the exposure has occurred and seeks medical attention for this reason. The presenting symptoms may be diverse, making diagnosis more difficult when there is no history or suspicion of radiation exposure,. Different radiation accident cases have been initially diagnosed as flu (nausea, vomiting), gastroenteritis, mumps, skin ulceration, burns and bone-marrow depression.
In many instances, the radiation dose must be measured from its biologic effects, because at the time of exposure, the person was not wearing a monitoring device that could measure radiation. The earliest indicator is the absolute lymphocyte count, which is a relatively accurate estimator for doses up to 3 Gy. With exposures greater than 3 Gy, peripheral granulocyte analysis is a more accurate estimator.
Treatment
Treatment of radiation injuries varies according to whether there has been whole-body or partial exposure, internal or external exposure, or a combination of both; the type of radiation; and the duration of exposure. Hemorrhage, shock, damage to the airway and other life-threatening injuries should be managed at the scene in the usual fashion.
Infection Control
Most patients who die from radiation injury, except those involved in high-dose nuclear criticality accidents, die of sepsis (systemic infection). Eliminating or reducing all possible sources of infection, either environmental or from the patient, is imperative.
Since the immune system is depressed due to the effects of exposure, there are greater risks for colonization of the respiratory tree. Wound contamination, including colonization of eschar (the crust that forms over a thermal burn wound) and nondebrided necrotic tissue, and intestinal colonization become even greater risks in the irradiated patient. Invasive monitoring and therapeutic devices, particularly if they are in-dwelling, also pose greater risks.
Control of bacterial translocation from an irradiated gastrointestinal tract into the systemic circulation, with subsequent sepsis, presents a unique set of problems. Clean drinking water is mandatory. Paralytic ileus (obstruction of the bowel from paralysis of the bowel wall) and decreased absorption of nutrients may prompt consideration of total parenteral nutrition, although this increases the risk of infection from the catheter.
Maintenance of normal gastrointestinal flora and selective decontamination of enteral pathogens is desirable.Anovel (in the United States) method of gastrointestinal pathogen suppression is the deliberate installation of nonpathogenic bacteria (probiotics) into the gut. Selected strains of Lactobacillus and Bifidobacteria have been shown to increase survival rates and prolong survival in animal studies.
Whole-body radiation and localized abdominal radiation are known to alter the intestinal ecology, decreasing the numbers of anaerobes and increasing the number of aerobic and facultative organisms. Administration of these probiotics normalizes the intestinal flora (Reeves, 1999). Immediately upon detection of fever in an irradiated neutropenic patient, cultures of body fluids, skin lesions and orifices as appropriate should be done; a review of the local hospital patterns of nosocomial (infection originating in a hospital) infections is in order. Broad-spectrum antibiotic coverage should begin promptly.
Prognosis
For low-dose levels of radiation exposure, the biologic effects are so small that they cannot be measured accurately. Higher accumulated doses of radiation, though they are not immediately fatal, may result in carcinogenesis, cataracts, genetic mutations and other effects that may not be apparent for many years following exposure. The table below summarizes the effects of various doses on an individual due to radiation accidents or nuclear war:
Effects of Radiation Doses
< 50 rads (< 0.5 Gy) Generally no clinical effect; subject asymptomatic.
50-100 rads (0.5-1.0 Gy) Mild nausea; white blood cell count (WBC) increases, then decreases.
100-200 rads (1-2 Gy) Nausea and vomiting; fatigue; WBC increases, then decreases.
200-400 rads (2-4 Gy) 2 to 3 days of nausea and vomiting, fatigue, WBC and platelets decreased; epilation, diarrhea, bleeding; recovery period 1-3 weeks.
300-500 rads (3-5 Gy) Lethal dose to 50 percent of the people exposed.
400-600 rads (4-6 Gy) Severe nausea, vomiting and diarrhea, sore throat, WBC and platelets decreased, symptoms recur, hemorrhages; recovery period brief or absent. Death to most in < 30 days.
600-1,000 rads (6-10 Gy) Severe and continuing nausea, vomiting and diarrhea; death to most in 1 to 10 days.
> 1,000 rads (> 10 Gy) Severe illness, disorientation, ataxia, burning sensation, shock; all die, most in 10 to 36 hours.
Source: Fowler, J.: Biological Effects of Radiation. In: Wilson, M. (Ed.): Textbook of Nuclear Medicine. Philadelphia: Lippincott-Raven, 1998)
© Copyright 2011 LexisNexis. All rights reserved. Parts of this article were excerpted from Occupational Injuries and Illnesses (LexisNexis).
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