Emergency Preparedness 15:
Acute Radiation Syndrome Portal
The effect of radioactive materials on a person is dependent on the amount of radiation absorbed by the body (dose), amount of the body exposed, route of exposure, length of time of exposure, and type of radiation.1 The exposure can be either external (ie, radiation from outside the body from a blast or fallout) or internal (ie, radiation from food, water, or air taken into the body that is contaminated with radioactive fallout). In the case of nuclear explosions, death or injury may occur from the blast itself, from being hit by debris energized from the blast, or from the radiation generated by the blast. Initially, skin burns and eye injuries may be apparent, but numerous other radiation-caused sickness or sequelae may develop from minutes to days later.
Symptoms of radiation sickness—often referred to as Acute Radiation Syndrome or Sickness (ARS)—can be manifested in many organ systems. ARS is a potentially serious illness that occurs when most or all of the body receives a high dose of radiation over a short period of time, usually within minutes or even less. Patients who receive fractionated doses of therapeutic radiation are less likely to manifest significant symptoms of ARS. ARS may develop from accidental exposure (examples include Goiania, Brazil in 1987 and Chernobyl, USSR in 1986) or intentional exposure via terrorist attacks using nuclear materials or devices. The quicker symptoms appear, the worse the prognosis for patients of ARS. In addition to the illness and death that may occur (from days to months following exposure), late complications of high-dose radiation exposures may occur years later, increasing the victim’s risk of cancer or other health effects.1
Basic
Information about Radiation
To
understand a discussion about radiation illnesses, a basic
understanding of the units of radiation dosages and biological damage
is necessary.
Units of Radiation—Terminology
|
The basic unit used to describe radiation dosage is the RAD (Radiation Absorbed Dose). One RAD (or rad) is equivalent to 0.01 joules of energy per kilogram (0.01 J/kg). One hundred rads of radiation is called a Gray (Gy) and equals 1.0 J/kg of energy. The biological damage caused by radiation is termed REM or Radiation Equivalent Man. One RAD of radiation causes one REM of damage, or put another way, 0.01 J/kg of radiation causes one REM of damage. One hundred REM is called one Sievert (Sv), or put another way, 100 rads or one Gy of radiation causes one Sievert of biological damage.
For radiation exposure to be destructive, it must be penetrating (ie, able to reach internal organs) as occurs with high-energy x-ray, gamma rays, and neutrons. There is no known truly safe dose or threshold of radiation exposure. There is also a background amount of radiation that we are exposed to, at least to some degree. Examples of background radiation include:
Chest x-ray with a dose effect of 0.01 REM.
Barium enema with a dose effect of 0.8 REM.
Cardiac catheterization with a dose effect of 4.5 REM.
Smoking 1.5 ppd with a dose effect of 16.0 REM/year.
Average US natural background radiation is 0.36 REM/year.
Acute Radiation Syndrome
To
develop ARS, a person needs to receive a large dose of penetrating
irradiation to the entire body (or most of the body) over a very short
period of time (usually a matter of minutes).2 The tissues most
susceptible to radiation damage are rapidly dividing cells such as in
the bone marrow, gastrointestinal (GI) tract, and skin. The dose of
radiation necessary to develop ARS varies from person to person, but
the exposure usually must exceed 50 to 70 rads (0.7 Gy) to produce
observable, mild symptoms.2 The lethal dose of ionizing radiation that
kills 50% of humans within 60 days of exposure (if the patient receives
no medical care) is 2.5 to 5.0 Gy (250 to 500 rads).2 Doses of
radiation in excess of 10 Gy (>1000 rads) are universally fatal,
even with optimal medical care.2
ARS is frequently divided into four stages2:
Prodromal stage (stage of nausea, vomiting, and diarrhea): Classic symptoms of this early stage are nausea, vomiting, and varying degrees of diarrhea (depending on dose of radiation) that occur from minutes to days after radiation exposure.
Latent stage: During this stage, if the dose of radiation is not too great, the patient looks and feels healthy. While the patient may not be feeling ill, critical changes may be occurring in the bone marrow with the decline of some of the cell populations, especially the lymphocyte and the platelet precursors.3 Latent stage may last from a few hours to many days.
Manifest illness stage: During this stage, the patient’s symptoms will depend on the amount of radiation exposure he or she has received and which specific syndromes the patient manifests. (See Classic Acute Radiation Syndromes below.) These symptoms may last for many months.
Recover or death: Patients with a high level of radiation exposure may require many months or years to recover or may not survive, even with the best medical care.
Classic Acute Radiation Syndromes
Bone marrow syndrome (hematopoietic syndrome): Bone marrow is highly sensitive to the effects of radiation and the earliest quantitative indicator for the degree of severity of ARS.3 The syndrome usually becomes apparent as the dose of radiation is increased above 0.7 Gy (70 rads), but mild effects may occur with exposures as low as 0.3 Gy (30 rads).2 Patient survival decreases with increasing dosages of radiation. The primary cause of death from ARS is due to the destruction of the bone marrow, resulting in infection and hemorrhage.2 The degree and rate of decline of the lymphocyte count is the most sensitive quantitative indicator of the degree of ARS and the risk of death. The absolute lymphocyte count vs. time during the first 48 hours post exposure is a very sensitive index to use to estimate the prognosis post exposure.2,3 The absolute lymphocyte count at 8 to 12 hours post-incident is especially helpful in estimating the patient’s total radiation exposure. Lymphocyte counts at 8 to 12 hours post-exposure suggest the following radiation exposure4:
Normal (≥ 2500) lymphocytes/mm3 = <1.0 Gy of exposure.
1700 to 2500 lymphocytes/mm3 = 1 to 5 Gy of exposure.
1200 to 1700 lymphocytes/mm3 = 5 to 9 Gy of exposure.
<1000 lymphocytes/mm3 = ≥ 10 Gy of exposure.
The development of a lymphocyte count of < 1000/mm3 at any time within the first 48 hours post-exposure is highly suggestive of an exposure of >2.0 Gy.4
The other very susceptible component of the bone marrow to radiation exposure is the platelets. Thrombocytopenia and the resulting hemorrhage can be a serious sequelae of radiation exposure.
Gastrointestinal syndrome: The symptoms resulting from the effects of radiation on the GI tract are due to the destruction of the lining cells with the potential of irreparable bowel chances. The GI symptoms associated with ARS are initially manifested as anorexia, nausea, vomiting, and diarrhea. Vomiting and diarrhea may result in severe dehydration, electrolyte imbalance, and increased susceptibility to infection.2 Timing of the onset of symptoms post radiation exposure is useful in estimating the dose of radiation the patient has received and (to some extent) the patient’s prognosis and chances for survival. Nausea and vomiting is usually the first symptom to appear. Patients who report vomiting within 4 hours or less of radiation exposure are at risk of serious GI ARS and need careful evaluation, monitoring, and treatment. Those who do not vomit until after the first 4 hours post exposure are, at worst, likely to have only a mild ARS, so therapy may be delayed if need be.3
Estimation of radiation dose based on the timing of the onset of vomiting and diarrhea3
Patients who have onset of vomiting > 2 hours after exposure usually have had no more than 2 Gy of radiation.
Patients who have onset of vomiting within 1 to 2 hours after exposure have likely had a 2 to 4 Gy dose of radiation.
Patients who have onset of vomiting < 1 hour after exposure have likely had a 4 to 6 Gy dose of radiation.
Patients who have onset of vomiting < 10 minutes after exposure have usually had > 8 Gy dose of radiation and have a poor prognosis for survival.
Patients who have onset of mild diarrhea 3 to 8 hours post exposure have likely had 4 to 6 Gy of radiation.
Patients who have onset of severe diarrhea < 1 hour post exposure have likely had > 8 Gy of radiation and have a poor prognosis.
Central nervous system/cardiovascular syndrome: The development of central nervous system (CNS) symptoms post radiation exposure is a poor prognostic sign, since the symptoms rarely develop without a large dose (probably lethal) of radiation. In its mildest form, CNS manifestations of ARS include headache and nervousness and usually suggest that the patient has experienced at least 4 to 6 Gy of radiation exposure.3 More severe CNS symptoms—including confusion, altered level of consciousness, seizures, and coma—are usually indicative of > 50 Gy of radiation exposure. These symptoms are due to increased intracranial pressure (ICP) secondary to the radiation-induced edema, vasculitis, and meningitis resulting in brain herniation.2 The onset of the CNS symptoms is usually within 5 to 6 hours after exposure, with death, due to circulatory collapse, occurring within 3 days. The chance for long-term survival in these cases is virtually zero.2
Cutaneous radiation syndrome2: Some skin damage is common with ARS. It is possible to have skin damage without developing signs or symptoms in the bone marrow or GI tract, especially if the acute exposure has been to beta radiation or x-rays. The initial skin manifestation of radiation is erythema, often associated with itching. This may progress to intense redness, blistering, and ulceration. Large cutaneous doses of radiation can cause hair loss, skin pigmentation changes, skin fibrosis, atrophy, ulceration, necrosis, and permanent damage to sweat and sebaceous glands.
Management of Acute Radiation Syndrome2
Initial management of patients exposed to radiation consists of implementing the ABCs (securing airway, breathing, and circulation), careful monitoring of vital signs, as well as treatment of respiratory injury, major burns, and other injuries. Special considerations in the management of ARS include:
With any radiation exposure, pay particular attention to decontamination of the patient and protection of the provider team. At a minimum, patients should have their clothes removed and their hair and skin safely decontaminated.
Initial lab work includes a routine trauma battery including a complete blood count (CBC), with close monitoring of the lymphocyte and platelet count. Electrolytes should be carefully monitored. Obtain blood gases as needed. Consider drawing blood for HLA (human leukocyte antigen) testing before any initial transfusion, just in case the patient becomes a candidate for bone marrow transplant at some later time.
Pay special attention to the reported time of the radiation exposure, the time of the onset of ARS symptoms (especially vomiting and diarrhea), and severity of ARS symptoms. This information is helpful in determining future care choices and predicting prognosis.
If you suspect the patient has had a large radiation dose (> 0.3 Gy or 30 rads), draw a CBC every 2 to 3 hours for the first 12 hours and every 4 to 6 hours for the following 48 hours. Closely monitor lymphocyte and platelet counts.
Treat vomiting and diarrhea with fluids and electrolytes as needed.
If possible, consult with radiation, hematology, and radiotherapy experts regarding radiation dose calculations, treatment options, and prognosis.
Call the Radiation Emergency Assistance Center/Training Site (REAC/TS) at (865) 576-3131 (M-F, 8 AM to 4:30 PM EST) or (865) 576-1005 (after hours) to record the incident in the Radiation Accident Registry System.
Consider whether palliative therapy is the most appropriate in select cases. (See below.)
Additional considerations in the treatment after the initial resuscitation of the patient include:
Provide care in a clean environment. A burn unit would be effective if available.
Patients who need emergency surgery should have it within 24 to 48 hours post radiation exposure. If this is not possible, wait for the patient’s bone marrow to recover, which usually takes three months.3
Prevent and treat infections.
Give blood and platelets as needed.
Monitor for skin changes and watch for skin breakdown.
Consider the use of growth factors to stimulate hematopoiesis.
Consider the use of stem cell transfusions.
Provide psychological support.
Consideration of Palliative Care
If the patient’s radiation exposure has been > 8 to 10 Gy (800 to 1000 rads), the probability of survival is extremely poor.2,3 A rough guide to the chances of survival includes3:
With no or only mild signs and symptoms of nausea and vomiting for the first few hours after radiation exposure, patients have probably received < 2 Gy of whole body radiation, and prognosis for survival is good.
With the onset of nausea and vomiting < 2 hours after exposure, and with these symptoms persisting longer than 24 to 48 hours, patients have likely received 2 to 8 Gy of whole body radiation, and survival probability is fair (but possible).
With early, severe, persistent vomiting (especially beginning < 10 minutes post exposure), severe diarrhea, shock, decreased level of consciousness, or coma, patients have most likely received > 8 Gy of whole body radiation, and chances for survival are improbable.
A number of signs and symptoms are associated with almost 100% death rate in patients receiving large doses of radiation (> 8 to 10 Gy). Consider palliative care for patients with the following symptoms, especially if medical resources are limited2,3:
Severe, persistent vomiting with onset < 10 minutes after radiation exposure,
Onset of severe diarrhea < 1 hour post exposure,
Temperature of > 38.5°C with onset < 1 hour post exposure,
Unconscious within minutes post exposure without a definable cause,
Development of severe headache with the onset < 1 hour post exposure,
Development of shock,
Development of coma,
Development of a lymphocyte count of < 1000 in the first 8 to 12 hours post exposure, and
Development of a platelet count < 20 000.
The care of patients with manifestations of ARS frequently requires the use of extensive medical resources. In situations where medical resources are limited, the difficult decision of offering only palliative care to the patients who have experienced the greatest exposure may be necessary in order to provide the needed care to potentially salvageable patients. As soon as time allows, obtain consultation to assist in the decision-making process.
References
- Frequently Asked Questions About a Nuclear Blast. Available at: www.bt.cdc.gov/radiation/nuclearfaq.asp. Accessed on: August 14, 2004.
- Acute Radiation Syndrome: A Fact Sheet for Physicians. Available at: www.bt.cdc.gov/radiation/arsphysicianfactsheet.asp. Accessed on: August 14, 2004.
- Walter FG. Advanced HAZMAT Life Support Provider Manual. Ed 2. 2000.
- Ricks RC, et al. The Medical Basis for Radiation Accident Preparedness: The Clinical Care of Victims. NY: Parthenon Publishing, 2002.