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Nerve Agent Effects
The nerve agent's mechanism of action is to inhibit the enzyme acetyl cholinesterase. Inhibition of this enzyme allows the neurotransmitter acetylcholine, to accumulate at the nerve endings where it causes excessive stimulation of the target organ. The parts of the body that are affected by excessive acetylcholine accumulation are as follows:
Eyes Nose (glands) Mouth (glands) Respiratory tract Gastrointestinal tract Cardiac muscle Sweat glands Skeletal muscle Central nervous system
The primary concern of a first responder when treating the nerve-agent poisoned casualty is to provide correct, timely, and lifesaving care. The fi rst step in providing this care is to understand the effects that a vapor- or liquid-nerve-agent exposure has on the casualty.
Understanding when these effects can most occur is critical in providing emergency care. The length of time a casualty may be in your care is unknown. It is best to understand what may occur and when, because being surprised by and unprepared for the reactions of a nerve agent poisoned casualty decreases chances for survival.
When a lethal or near-lethal exposure occurs, the time to onset of symptoms and maximal severity of symptoms may be extremely brief. If aggressive care is not given to the casualty exposed to a lethal concentration, death can result within five minutes after the appearance of symptoms.
Eyes
The eyes will be affected by direct contact with a nerve agent vapor or aerosol. When the route of entry of the agent is through the skin or by ingestion, the effect on the eyes is delayed or may not occur.
The main effect of the agent is to cause pinpointing of the pupils (miosis). One or both pupils may be pinpointed and unresponsive to light or darkness. Pinpointing causes a complaint of dim vision that is more pronounced in low light conditions.
Frontal headache, mild aching around the eye, or severe pains are common complaints in a casualty exposed to a moderate concentration of agent. Twitching of the eyelids may be observed and the eyes may be reddened.
When a light source is used to test for pupil response, the casualty may complain of an increase in aching behind the eyes due to light sensitivity.
Nose and Mouth
The secretor glands of the nose and mouth are as sensitive as or more sensitive to nerve agent vapor or aerosol than the eyes are. When the casualty is poisoned by nerve agent liquid on the skin or by ingestion, the nose will become affected, but only in response to systemic involvement.
When exposed to a nerve agent vapor or aerosol, the nose will begin to run (rhinnorhea). This effect has been described by casualties recovering from accidental nerve agent vapor exposure as "worse than a cold or hay fever" and "like a leaking faucet." Even after low concentrations of agent have been absorbed, running nose may be severe.
The mouth will secrete excessive amounts of saliva that may be so copious that watery secretions run out the corners of the mouth.
Respiratory Tract
Inhalation of a small amount of nerve agent vapor will cause the casualty to complain of tightness in the chest or shortness of breath. This occurs because the excessive acetylcholine stimulates the muscles in the airways to contract and constrict the airways (bronchoconstriction).
As the concentration increases, breathing diffi culty will become severe. One or two breaths of a high concentration of nerve agent vapor will cause gasping and irregular respirations within seconds to a minute or two.
WARNING! Cessation of breathing can occur within minutes after exposure to a large amount of nerve agent, either by vapor inhalation or skin contact.
Excessive bronchial and upper airway secretions caused by stimulation of the airway glands by the excessive acetylcholine will compound breathing diffi culty. These secretions can obstruct the airway and cause diffi culty in moving air into and out of the lungs, with prolonged expiration a noticeable effect.
Gastrointestinal (GI) Tract
After exposure to a large but non-lethal concentration of vapor, the casualty will complain of nausea and may vomit.
Nausea and vomiting may be the fi rst effects from liquid nerve agent exposure on the skin. The casualty may complain of nausea followed by vomiting, heartburn, and abdominal pain. In addition, the casualty may belch frequently and have diarrhea or involuntary defecation and urination. These effects usually occur within several minutes after vapor exposure. However, after liquid agent exposure on the skin, these effects may not begin for as long as 18 hours after exposure.
Cardiac
The heart rate can either increase or decrease after nerve agent exposure. Generally, blood pressure will increase. The heart rate in nerve agent poisoning will not aid the casualty or first responder/doctor in choosing the care needed.
Sweat Glands
The skin is very permeable to nerve agents. When penetration occurs after exposure to either liquid or vapor, localized sweating occurs and progressively spreads over the surrounding skin area as nerve agent is absorbed.
Skeletal Muscles
After exposure to a moderate or large amount of nerve agent, the casualty will complain of weakness and twitching of muscle groups. The twitching can first be noticed at the site of a liquid droplet on the skin. The muscles may show a rippling effect. As the nerve agent effect progresses, muscles can go into a prolonged contraction. However, instead of a prolonged contraction, the large muscle groups may begin unsynchronized contractions that cause the arms and legs to flail about. The hyperactivity of the muscles in these instances leads to muscle fatigue and flaccid paralysis. Without aggressive medical treatment, the casualty will not survive.
Central Nervous System (CNS)
In the case of a large inhalation or liquid dose, the effects are rapid and usually fatal. The casualty almost immediately loses consciousness, followed seconds later by seizure activity. Several minutes later, respiration ceases.
Without immediate care, the casualty will not survive to reach treatment. When exposed systemically to low amounts of nerve agent, the casualty may complain of generalized weakness.