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| Emergency Medical Services and Trauma ● Health Alert Network ● Health Hotline ● Emergency Preparedness & Response |
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Behavior of Nerve Agents in the Body Mechanism of Action A characteristic of nerve agents is that they are extremely toxic and that they have very rapid effect. The nerve agent, either as a gas, aerosol or liquid, enters the body through inhalation or through the skin. Poisoning may also occur through consumption of liquids or foods contaminated with nerve agents. The route for entering the body is of importance for the period required for the nerve agent to start having effect. It also influences the symptoms developed and, to some extent, the sequence of the different symptoms. Generally, the poisoning works faster when the agent is absorbed through the respiratory system than via other routes. This is because the lungs contain numerous blood vessels and the inhaled nerve agent can therefore rapidly diffuse into the blood circulation and thus reach the target organs. Among these organs, the respiratory system is one of the most important. If a person is exposed to a high concentration of nerve agent, e.g., 200 mg sarin/m3 (see table) death may occur within a couple of minutes. Poisoning takes longer when the nerve agent enters the body through the skin. Nerve agents are more or less fat-soluble and can penetrate the outer layers of the skin. However, it takes some time before the poison reaches the deeper blood vessels. Consequently, the first symptoms do not occur until 20-30 minutes after the initial exposure but subsequently the poisoning process may be rapid if the total dose of nerve agent is high. The toxic effect of nerve agents depends on them becoming bound to an enzyme, acetylcholinesterase, and thereby inhibit this vital enzyme's normal biological activity in the cholinergic nervous system. Symptoms When exposed to a low dose of nerve agent, causing minor poisoning, characteristic symptoms are increased production of saliva, a running nose and a feeling of pressure on the chest. The pupil of the eye becomes contracted (miosis) which impairs night-vision. The accommodation capacity of the eye is also reduced so that short-range vision deteriorates and the victim feels pain when he tries to focus on an object nearby. This is accompanied by headache. More unspecific symptoms are tiredness, slurred speech, hallucinations and nausea. Exposure to a higher dose leads to a more dramatic development and symptoms are more pronounced. Bronchoconstriction and secretion of mucous in the respiratory system leads to difficulty in breathing and to coughing. Discomfort in the gastrointestinal tract may develop into cramp and vomiting. Involuntary discharge of urine and defecation may also form part of the picture. The discharge of saliva is powerful and the victim may experience running eyes and sweating. Symptoms from the skeletal muscles are very typical. If the poisoning is moderate, this may express itself as muscular weakness, local tremors or convulsions. When exposed to a high dose of nerve agent, the muscular symptoms are more pronounced. The victim may suffer convulsions and lose consciousness. To some extent, the poisoning process may be so rapid that earlier mentioned symptoms may never have time to develop. Muscular paralysis caused by nerve agents also affects the respiratory muscles. Nerve agents also affect the respiratory center of the central nervous system. The combination of these two effects is the direct cause of death. Consequently, death caused by nerve agents is a kind of death by suffocation. The figure shows examples of poisoning results caused by different doses of sarin vapor. In similarity to other poisons, different individuals are more or less sensitive to nerve agents. The figure shows that the lethal dose for the most sensitive individuals is about 70 mg.min/m3 and about twice this level for more resistant people. The toxic effect depends on both the concentration of nerve agent in the air inhaled (C) and the time of exposure (t). In extremely high concentrations there is a simple relationship, C t, which gives a certain toxic effect. Inhalation of sarin vapor with a concentration of 100 mg/m3 for one minute gives the same result as inhalation of 50 mg/m3 for two minutes. However, at low concentrations this relationship does not apply since the human body is capable of some degree of detoxification. In order to obtain a corresponding effect, it is then necessary to have relatively longer periods of exposure. The values given in the table for toxicity of nerve agents apply to high concentrations.
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Emergency Preparedness & Response Section |
Copyright � 2005 North Dakota Department of Health |
