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The doses of radiation which will result in the gastrointestinal syndrome are higher than those causing the hematopoietic syndrome. An acute dose which will cause this syndrome would be at least 800 cGy. Regardless of the dose involved, the gastrointestinal syndrome has a very serious prognosis because it is almost always accompanied by non recoverable bone-marrow.
The onset of the gastrointestinal syndrome occurs earlier than that of the hematopoietic syndrome. After a latent period of a few days to a week, the characteristic severe fluid losses, hemorrhage and diarrhea begin.. There is no specific clinical sign of radiation-caused gastrointestinal damage. However, a peripheral blood count done on these patients may show severe pancytopenia because of bone-marrow depression.
A problem in diagnosis will arise in patients with sub lethal hematopoietic depression due to radiation and diarrhea due to some other cause such as infection. It would be difficult to differentiate patients with lethal radiation sickness from those with potentially nonlethal radiation sickness complicated by dysentery. Microscopic examination of the diarrhea may reveal inflammatory cells which is suggestive of dysentery.
This syndrome is associated only with very high acute doses of radiation. The lower limit is probably 2000 to 3000 cGy, The latent period is very short varying from several hours to 1 to 3 days. The subsequent clinical picture is basically that of a steadily deteriorating state of consciousness with eventual coma and death. Convulsions may or may not occur. There may be little or no indication of increased intracranial pressure. Because of the very high doses of radiation required to cause this syndrome, personnel close enough to a nuclear explosion to receive such high doses would generally be well within the range of 100% lethality due to blast and thermal effects .
The diagnosis of radiation sickness is based primarily upon the clinical picture presented by the patient. A precise history of exposure may be very difficult to obtain, since many individuals may not know that they actually have been exposed to radiation, particularly if the exposure is due to fallout. The physical findings and characteristics of the various forms of radiation sickness are described below, along with such laboratory findings as may occur. Dosimetry, at the present time, will not give adequate information to determine either the extent of radiation injury or the prognosis. Dosimeters cannot tell whether a radiation exposure is whole body or partial body. They do not tell what the dose rate of the exposure was. Consequently, the following guidelines would apply to medical personnel operating in austere field conditions. Lymphocyte levels may be used as a biologic dosimeter to confirm the presence of pure radiation injury but not in combined injuries.
(a) Lymphocyte levels in excess of 1500/mm3 (cubic millimeters) : The patient most likely has not received a significant dose that would require treatment.
(b) Lymphocyte levels between 1000 and 1500/mm3 : The patient may require treatment for moderate depression in granulocytes and platelets within 3 weeks post exposure.
(c) Lymphocyte levels between 500 and 1000/mm3 : The patient will require treatment for severe radiation injury. The patient should be hospitalized to minimize the complications from hemorrhage and infection that will arise within 2-3 weeks post exposure.
(d) Lymphocyte levels of less than 500/mm3 : The patient has received a radiation dose that may prove fatal. The patient needs to be hospitalized for the inevitable pancytopenic complications.
(e) Lymphocytes not detectable : The patient has received a super lethal radiation dose, and survival is very unlikely. Most of these patients have received severe injuries to their gastrointestinal and cardiovascular systems and will not survive for more than 2 weeks.
(f) Other Guidelines. A useful rule of thumb is, if lymphocytes have decreased by 50% and are less than 1000/mm3, then the patient has received a significant radiation exposure. In the event of combined injuries, the use of lymphocytes may be unreliable.
It is difficult to establish an early definitive diagnosis. Therefore, it is best to function within a simplified, tentative classification system based on the three possible categories of patients discussed below:-
(a) Radiation Injury Unlikely
If there are no symptoms associated with radiation injury, patients are judged to be at minimal risk for radiation complications. These patients should be triaged according to the severity of the conventional injuries. If the patients are free of conventional injuries or disease states that require treatment, they should be released and returned to duty.
(b) Radiation Injury Probable
Anorexia, nausea, and vomiting are the primary prodromal symptoms associated with radiation injury. Priority for further evaluation will be assigned after all life-threatening injuries have been stabilized. Casualties in this category will not require any medical treatment within the first few days for their radiation injuries. Evidence to support the diagnosis of significant radiation injury in the absence of burns and trauma may be obtained from lymphocyte assays taken over the next 2 days. If the evidence indicates that a significant radiation injury was received, these casualties need to be monitored for pancytopenic complications.
(c) Radiation Injury Severe
These casualties are judged to have received a radiation dose that is potentially fatal. Nausea and vomiting will be almost universal for persons in this group. The prodromal phase may also include prompt explosive bloody diarrhea, significant hypotension, and signs of necrologic injury. These patients should be sorted according to the availability of resources. Patients should receive symptomatic care. Lymphocyte analysis is necessary to support this classification .
Summary of Acute Whole Body Exposure Effects
Below 100 REMS
In this dose range no obvious sickness occurs. Detectable changes in blood cells begin to occur at 25 rems, but occur consistently only above 50 rems. These changes set in over a period of days and may require months to disappear. Depression of sperm production becomes noticeable at 20 rems, an exposure of 80 rems has a 50% chance of causing temporary sterility in males.
Mild acute symptoms occur in this range. Tissues primarily affected are the hematopoietic (blood forming) tissues, sperm forming tissues are also vulnerable. Symptoms begin to appear at 100 rems, and become common at 200 rems. Typical effects are mild to moderate nausea (50% probability at 200 rems), with occasional vomiting, setting in within 3-6 hours after exposure, and lasting several hours to a day. This is followed by a latent period during which symptoms disappear.. Mild clinical symptoms return in 10-14 days. These symptoms include loss of appetite (50% probability at 150 rems), malaise, and fatigue (50% probability at 200 rems), and last up to 4 weeks. Recovery from other injuries is impaired and there is enhanced risk of infection. Temporary male sterility is universal.
Illness becomes increasingly severe, and significant mortality sets in. Hematopoietic tissues are still the major affected organ system. Nausea becomes universal (100% at 300 rems), the incidence of vomiting reaches 50% at 280 rems. The onset of initial symptoms occurs within 1-6 hours, and last 1-2 days. After this a 7-14 day latency period sets in. When symptoms recur, the may include epilation (hair loss, 50% probability at 300 rems), malaise, fatigue, diarrhea (50% prob. at 350 rems), and hemorrhage (uncontrolled bleeding) of the mouth, subcutaneous tissue and kidney (50% prob. at 400 rems). Suppression of white blood cells is severe, susceptibility to infection becomes serious. At 300 rems the mortality rate without medical treatment becomes substantial (about 10%). The possibility of permanent sterility in females begins to appear. Recovery takes 1 to several months.
Mortality rises steeply in this dose range, from around 50% at 450 rems to 90% at 600 (unless heroic medical intervention takes place). Hematopoietic tissues remain the major affected organ system. Initial symptoms appear in 0.5-2 hours, and last up to 2 days. The latency period remains 7-14 days. The symptoms listed for 200-400 rems increase in prevalence and severity, reaching 100% occurrence at 600 rems. When death occurs, it is usually 2-12 weeks after exposure and results from infection and hemorrhage. Recovery takes several months to a year, blood cell counts may take even longer to return to normal. Female sterility becomes probable.
Survival depends on stringent medical intervention. Bone marrow is nearly or completely destroyed, requiring marrow transfusions. Gastrointestinal tissues are increasingly affected. Onset of initial symptoms is 15-30 minutes, last a day or two, and are followed by a latency period of 5-10 days. The final phase lasts 1 to 4 weeks, ending in death from infection and internal bleeding. Recovery, if it occurs, takes years and may never be complete.
Above 1000 REMS
Very high exposures can cause sufficient metabolic disruption to cause immediate symptoms. Above 1000 rems rapid cell death in the gastrointestinal system causes severe diarrhea, intestinal bleeding, and loss of fluids, and disturbance of electrolyte balance. These effects can cause death within hours of onset from circulatory collapse. Immediate nausea occurs due to direct activation of the chemoreceptive nausea center in the brain.
In the range 1000-5000 rems the onset time drops from 30 minutes to 5 minutes. Following an initial bout of severe nausea and weakness, a period of apparent well-being lasting a few hours to a few days may follow (called the ââ‚¬Å“walking ghostââ‚¬ phase). This is followed by the terminal phase which lasts 2-10 days. In rapid succession prostration, diarrhea, anorexia, and fever follow. Death is certain, often preceded by delirium and coma. Therapy is only to relieve suffering.
Above 5000 rems metabolic disruption is severe enough to interfere with the nervous system. Immediate disorientation and coma will result, onset is within seconds to minutes. Convulsions occur which may be controlled with sedation. Victim may linger for up to 48 hours before dying .
Initial Treatment for Patients With Whole-Body Radiation Injury
The primary determinants of survival among most patients receiving intermediate (serious but not uniformly fatal if treated) radiation doses is management of microbial infections and stopping any bleeding. If high intermediate doses have been received, fluid and electrolyte loss may cause early deaths. If properly resuscitated, however, these patients may survive until the consequences of hematologic failure become apparent.
For those casualties who have received sub lethal whole-body radiation doses, gastrointestinal distress will predominate in the first 2 days. Antiemetics (metoclopropamide, dazopride) may be effective in reducing the symptoms, but present drugs available have significant side effects. Unless severe radiation injury has occurred, these symptoms will usually subside within the first day. For those patients who continue to experience gastrointestinal distress, parenteral fluids should be considered. If explosive diarrhea occurred within the first hour post exposure, fluids and electrolytes should be administered if available. For triage purposes, the presence of explosive diarrhea (especially bloody) is likely to be related to a fatal radiation dose.
Cardiovascular support for patients with clinically significant hypotension and neurological dysfunction should be undertaken only when resources and staff allow. These patients are not likely to survive injury to the vascular and gastrointestinal systems combined with marrow aplasia [4,5 &6].
Management of Infection
In spite of antibiotics, infections with opportunistic pathogens are still a major problem. The majority of these organisms today are gram-negative. These infections occur as a consequence of both profound immunosuppression and abnormal colonization of body surfaces and invasive medical devices. Susceptible body surfaces include the oropharyngeal-respiratory tree and the intestine. Wound sites and artificial invasive devices such as catheters are also important sources of infection. Wound debridement, dressings, and, when necessary, antibiotics are key elements in infection control. Antibiotics, preferably in appropriate combination in therapy, should be used promptly to treat any new fever. When signs or symptoms of infection do appear in the granulocytopenic patient, treatment should be started without waiting for culture and sensitivity studies. Initial coverage should include gram-negative organisms and Staphylococcus aureus. Prevalent organisms and antimicrobial susceptibility patterns in the particular medical facility should also be considered. It is recommended either that the treatment continue until the granulocytes return to more than 500 or treat for just 2 weeks and stop even if the white cell count is still low, as long as all signs of infection have cleared [5 & 6].