Chemical Warfare (cont.)
The 5 nerve agents, tabun (GA), sarin (GB), soman (GD), cyclohexylsarin (GF), and VX, have chemical structures similar to the common organophosphate pesticide Malathion. These agents initially stimulate and then paralyze certain nerve transmissions throughout the body and cause other toxic effects such as seizures.
- Physical properties: Under temperate conditions, all nerve agents are volatile liquids, which means they can evaporate quickly. The most volatile agent, sarin, evaporates at about the same rate as water. The least volatile agent, VX, has the consistency of motor oil, which makes it 100-150 times more toxic than sarin when victims are exposed on their skin. A 10 mg dose applied to the skin may cause death in up to half of unprotected people. All nerve agents rapidly penetrate skin and clothing. Nerve agent vapors are heavier than air and tend to sink into low places (for example, trenches or basements).
- Signs and symptoms: Nerve agents produce various signs and symptoms depending on the agent someone might be exposed to, its concentration, and length of exposure.
- Liquid exposure: Liquid agents easily penetrate skin and clothing. Symptoms may begin anywhere from 30 minutes to 18 hours after skin exposure. A small droplet on the skin, for example, may cause local sweating and muscle twitching, followed by nausea, vomiting, diarrhea, and generalized weakness. Even with decontamination, signs and symptoms may last for hours. In contrast, people with severe liquid exposures may show no symptoms (for 1-30 minutes) but rapidly may suffer abrupt loss of consciousness, convulsions, generalized muscular twitching, paralysis, secretions (from the nose, mouth, lungs), difficulty breathing, and death.
- Vapor exposure: Vapor inhalation produces poisonous symptoms within seconds to several minutes. Effects may be local or throughout the body. Exposure to even a small amount of vapor usually results in at least one of the following categories of symptoms: (1) in the eyes, blurred vision, eye pain, red eyes; (2) runny nose; or (3) difficulty breathing, shortness of breath, excessive productive coughing.
- Respiratory tract: Nerve agents act on the upper respiratory tract to produce runny nose, drooling, and weakness of the tongue and throat muscles. High-pitched, distressed breathing can occur. A great deal of phlegm production and narrowing of the airways can occur. If untreated, the combination of symptoms rapidly progresses to respiratory failure and death.
- Cardiovascular system: Nerve agents also act on the heart and may produce abnormal heartbeats, more likely to be too fast rather than slow.
- Central nervous system: Nerve agents produce a variety of signs and symptoms throughout the central nervous system. People may lose consciousness (sometimes within seconds of exposure) and have seizures. Symptoms such as headache, dizziness, numbness or tingling, anxiety, insomnia, depression, and emotional instability also have been reported.
- Musculoskeletal system: Nerve agents initially stimulate and then paralyze muscles. With minimal exposure, exposed people may complain of vague weakness or difficulty walking.
- Eyes: Nerve agent liquid or vapor readily penetrates the eye tissues and may cause the pupils to contract, blurred and dim vision, headache, redness, tears, pain, nausea, and vomiting. Although contraction of the pupils is the most consistent clinical finding after vapor exposure to nerve agents (this occurred in 99% of people exposed in the Tokyo sarin attack), it may not occur or occur later if the exposure is on the skin. In severe cases, the pupils of the eye may remain narrowed up to 45 days.
- Diagnosis: Routine testing is not reliable in identifying nerve agents in blood or urine. So doctors will make their treatment decisions based on the signs and symptoms a person shows and on information about the type of chemical exposure, if known.
- Treatment: Treatment of victims exposed to nerve gas is similar to the treatment of those poisoned by organophosphate insecticides.
- Atropine sulfate: Victims with symptoms require immediate treatment with atropine. Atropine helps people breathe by drying secretions and opening their airways to allow them to breathe more freely. Atropine also blocks other effects of poisoning, such as nausea, vomiting, abdominal cramping, low heart rate, and sweating. Atropine, however, does not prevent or reverse paralysis. Adults and children will be given appropriate doses of atropine by IV or injection. Another medication, pralidoxime chloride, may also be given. With adequate decontamination and appropriate initial therapy, serious signs and symptoms of nerve agent toxicity rarely last more than a couple of hours.
- Mark I kit: The Mark I kit was designed for military self-administration in the field. It consists of 2 spring-loaded devices to inject yourself, containing atropine and pralidoxime, respectively. These antidote kits are not yet available for civilian use.
- Prognosis: Peak toxic effects occur within minutes to hours and go away within 1 day. People who were exposed but show no symptoms are usually observed for at least 18 hours because some signs and symptoms can show up later.
Jeffrey L Arnold, MD, FACEP
Francisco Talavera, PharmD, PhD
Raymond J Roberge, MD, MPH, FAAEM, FACMT
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