Chemical Terrorism

By James A. Geiling, MD, FCCP

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Nerve Agents

Clinical Effects

Nerve agents possess chemical similarities and properties to organophosphate insecticide poisons, and hence have a similar clinical presentation. The symptom complex can be summarized by the "SLUDGE" toxidrome: increased salivation, lacrimation, urination, diarrhea, gastric distress, and emesis.¹²

The principal effect on the eyes is miosis as a consequence of direct contact with vapor. This rarely occurs with skin contact alone unless the exposure level is high. Symptoms begin within seconds to minutes and can be associated with sharp or dull pain (which may induce nausea or vomiting), dim and blurred vision, and conjunctival injection. Significant lacrimation also typically occurs.

Rhinorrhea may be the first respiratory sign and symptom, the significance being dose dependent. Also depending upon the dose and duration of exposure, bronchorrhea and bronchoconstriction develop. Skeletal muscle weakness further impairs breathing. CNS-mediated apnea may also occur.

Vagal input may decrease heart rate, although normally patients are tachycardic from a fight-or-flight mechanism or hypoxia. Blood pressure remains near normal until a terminal decline.

Increased salivary gland secretion and other evidence of GI glandular hypersecretion occur with exposure. Consequently, victims often experience nausea, vomiting, and diarrhea.

Localized sweating can occur at the site of exposure, but generalized sweating only presents with a large vapor or skin exposure. Skeletal muscles develop fasciculations and twitching initially, but later become weak and eventually flaccid.

Effects on the CNS vary with exposure. Small doses result in variable and nonspecific findings, such as an inability to concentrate, insomnia, bad dreams, irritability, impaired judgment, and depression. Large exposure may lead to a loss of consciousness, seizure activity, and apnea. Psychological and behavioral changes include anxiety, tenseness, fatigue, forgetfulness, irritability, and mild confusion. Complete disorientation and hallucinations do not occur.

Initial effects can be seen within seconds to minutes, and the rapidity and severity are dependent upon the dose. High-dose vapor exposure can lead to loss of consciousness and seizures within 1 min, whereas low-dose skin contact can present with GI complaints as long as 18 h after exposure. Very few other illnesses mimic nerve agent exposure, although low-dose sporadic cases may be initially be diagnosed as an upper respiratory illness, allergic syndrome, or gastroenteritis.

Laboratory findings include inhibition of red cell AChE activity, which may assist in establishing the diagnosis of early or confusing cases. Red cell AChE activity is more sensitive than plasma AChE activity in the presence of a nerve agent. Although helpful in establishing or confirming the diagnosis, inhibition of enzyme activity does not correlate with symptom severity. Other common laboratory abnormalities include hypoxia and respiratory acidosis as a consequence of the respiratory signs described above.

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