*A Beginner抯 Guide to Nerve Agents*
25 May 2004
Contrary to what people say, there is no "nerve gas". Chemical weapons known as nerve agents can exist as liquids, sprays, or vapors. Nerve agents are classified in two groups based on the rate at which they evaporate. The "G" agents; GA, GB, and GD, evaporate quickly and are non-persistent chemical weapons developed by the Germans in World War II. VX is an oily or persistent nerve agent developed after the war.
The military can employ a nerve agent through area bombardment with artillery or missiles or direct aerial application by bombing or aerial sprays. Heavy application of the agent is required to achieve a lethal concentration in an open area. When non-persistent "G" agents are deployed in the open, they are quickly degraded by UV light and simply evaporate in a short period of time.
Persistent nerve agent--VX--is a liquid of low volatility that, evaporating slowly, well, persists. The properties of VX are more akin to diesel fuel than a more volatile liquid such as water. VX evaporates very slowly and will contaminate your clothing and skin when you walk through the area where VX has been applied.
Terrorists have employed nerve agents with modest success in the past. Aum Shinrikyo, a Japanese religious sect, deployed Sarin (GB) in an apartment complex in 1994 and in a Tokyo subway in 1995.
In the first attack, 300 persons became ill with 7 fatalities reported. The 1995 subway attack caused 5,000 people to seek medical attention with 12 fatalities. More than 80% of those who sought medical care suffered no effect from the exposure. The Sarin (GB) used in the Tokyo subway was NOT deployed in an effective manner. Rather than dispersing the agent in an aerosol, it was left in jars to spill on the ground and evaporate.
In a terrorist event, for non--persistent agents to be effective, they must be aerosolized in a confined space like a subway or a ventilation system of a building.
Physiologic Effects of Nerve Agent Exposure
All nerve agents have two types of effects on the body; muscarinic and nicotinic. The muscarinic effect is on the "glands" and the nervous system. For nerve transmission to occur, an enzyme, acetylcholine is released by the nerve ending and stimulates the gland or muscle that the nerve controls. The nerve impulse is terminated as acetylcholine is "reactivated" by acetylcholinesterase. Nerve agent prevents the "reactivation " of acetylcholine with a resulting continued stimulation of the glands and nerves.
Nicotinic effects of a nerve agent are those exerted on the striated or skeletal muscle. These effects are twitching and jerking of the muscles, seizures, and paralysis. These effects may initially be local following skin exposure or generalized following inhalation of a nerve agent.
Muscarinic effects of exposure to nerve agent are increased salivation, water eyes, and a runny nose; shortness of breath, coughing, wheezing, and increased mucous production; diarrhea, urination, and chest tightness.
The nemonic "SLUDGE" helps us remember the effects of nerve agents.
S Salivation, sweating
D Defecation, drooling, diarrhea
G Gastric upset and cramps
Nerve agents are very deadly, a single drop of nerve agent on the skin, if not decontaminated and left untreated, you will likely die. The effect of an inhaled nerve agent is much more rapid and occurs in a few seconds following exposure. Simple as that. Fortunately, the treatment for nerve agent exposure is also very simple as you will see shortly.
Atropine injection is the mainstay of treatment for nerve agent injury. Atropine blocks the muscarinic effects of the nerve agent and prevents the "gland" effects of watery eyes, runny nose, diarrhea, and the deadly lung effects of increased mucous secretion and bronchospasm (wheezing). The nervous system effects are also blocked, preventing seizures.
The second therapeutic agent utilized is 2-PAM Chloride (2-pyridine Aldoxime Methyl Chloride). 2-PAM Chloride acts like a crowbar to break the bond between the enzyme acetylcholinesterase and nerve agent that prevents normal nerve functioning.
Atropine and 2-PAM Chloride automatic injectors comprise the Mark-1 nerve agent antidote kit utilized by the military and by first-responders. Atropine for treatment of nerve agent exposure does NOT need to come in a Mark I kit. Any atropine solution for injection is suitable.
Dilution is the Solution to Polution
It goes without saying we don抰 want any of the "awful-bad-stuff" on us when we treat or decontaminate patients, so adequate protective clothing, boots, gloves, and chemical masks are MANDATORY. Decontamination should occur UPWIND of the chemical concentration to avoid exposure of the medical folks and decontaminated patients.
The first and most important step in treatment is decontamination. Simply removing a victim抯 clothing will remove as much as 85% of the chemical agent. A detergent scrub (TIDE or DAWN) and fresh water rinse to remove any residual chemical from the skin allows medical treatment of the casualty to begin. If you want to be "double-sure" of your decontamination, spray the victim with a solution of 10% Clorox bleach in water.
Remember, a patient with vapor exposure only does not require decontamination!
After a patient is decontaminated, there is NO need for rescuers to wear masks, gloves, boots, or TYVEK suits when providing medical care.
Catching the runoff of a decontamination station may be required to avoid an OSHA fine in a HAZMAT event, but in the SHTF situation we are talking about, I would not attempt to contain or isolate runoff with a wading pool or other containment vessel.
Treatment of Nerve Agent Exposure
The treatment of nerve agent exposure is partly dependent on whether the exposure has been simply inhalation of a vapor or exposure to a liquid source of the chemical. If exposed to the vapor only, once exposure stops, the patient should not deteriorate significantly and more importantly after being disrobed, DOES NOT REQUIRE DECONTAMINATION!
--Mild Exposure to Vapor Only
Pinpoint pupils, runny nose, and mild respiratory distress requires only observation or administration of one Mark 1 kit (2 mg Atropine and 600 mg 2-PAM)
--Moderate Exposure to Liquid or Vapor
Shortness of breath, wheezing, diarrhea, and vomiting requires one Mark 1 kit every 5-10 minutes. A maximum dose of 3 injectors (1800 mg) 2-PAM is given. Additional atropine may be given to a total of 20 mg.
--Severe Exposure to Liquid or Vapor
The casualty is flaccid or seizing, not breathing, unconscious. Treatment is ventilation and administration of 3 Mark I kits and 10 mg of Diazepam to prevent seizures. Additional atropine can be given every 5-10 minutes. The patient with severe bronchospasm will benefit from nebulized aerosol treatments of albuterol or another available bronchodilator.
How Much Atropine is "Enough"?
We are not dealing with ACLS-doses of atropine in this case. Atropine should be given until the patient is "dry and breathing easy". That is, until their secretions have dried up; they are not drooling or dripping from the nose and they are no longer experiencing tightness in their chest or wheezing.
Remember, we are NOT treating a target heart rate and cannot gauge our treatment on pupil size! Beachdoc
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