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Nerve Agents - Prehospital Management

Acute Management Overview

Agent Identification

Nerve agents (NAs) are the most toxic of the known chemical warfare agents. They are chemically similar to organophosphate pesticides (OPs) and exert their biological effects by inhibiting acetylcholinesterase enzymes.

  • Nerve agents can cause loss of consciousness and convulsions within seconds and death from respiratory failure within minutes of exposure.

Volatile Nerve Agents (vapor)

  • Nerve agent vapor is readily absorbed by inhalation and ocular contact and produces rapid local and systemic effects.
  • G-type agents are clear, colorless and tasteless liquids that are soluble in water and most organic solvents.
  • GB is odorless and is the most volatile nerve agent; however, it evaporates at about the same rate as water. GA has a slightly fruity odor and GD has a slight camphor-like odor (not reliable signs).

Low Volatility Nerve Agents (liquid)

  • Liquid nerve agent is readily absorbed through the skin; however, effects may be delayed for several minutes to up to 18 hours.
  • VX is a clear, amber-colored, odorless, oily liquid. It is soluble in water as well as in all other solvents. It is the least volatile nerve agent.
  • Responders should obtain assistance in identifying the chemical(s) from container shapes, placards, labels, shipping papers, and analytical tests. General information on these identification techniques is located in Emergency Response Guidebook.
  • Identification Tools - CHEMM-IST, WISER, Nerve Agents Chemical Properties
  • Devices - M8, M9 chemical agent detector paper (liquid agents), M18A3 chemical agent detectors (vapor), M256A1 chemical agent detector kit (liquid and vapor), Draeger CDS Kit (vapor and aerosol), Hazmat Smart Strips (qualitative), Chemical Agent Detector C2 Kit (liquid and vapor), Chemical Agent Monitor (CAM) (vapor)
  • A comprehensive source for the selection of chemical identification equipment is the Guide for the Selection of Chemical Detection Equipment for Emergency First Responders, Guide 100-06, January 2007, 3rd Edition published by the Department of Homeland Security to assist with this process.

Rescuer Protection

Nerve Agent Specific Triage

Triage for Nerve Agent Casualties
Immediate (1) Effects - Unconscious, talking but not walking, moderate to severe effects in two or systems more systems (e.g., respiratory, GI, cardiac arrest. muscular, CNS)
Clinical Signs - seizing or postictal, severe respiratory distress, recent cardiac arrest
Delayed (2) Effects - recovering from agent exposure or antidote
Clinical Signs - diminished secretions, improving respiration.
Minimal (3) Effects - walking and talking
Clinical Signs - pinpoint pupils, runny nose, and mild to moderate difficulty breathing.
Expectant (4)
(limited resources)
Effects - Unconscious
Clinical Signs - Cardiac/respiratory arrest of long duration.


  • Victims whose skin or clothing is contaminated with liquid nerve agent can contaminate rescuers by direct contact or through off-gassing vapor.
  • Persons whose skin is exposed only to nerve agent vapor pose no risk of secondary contamination; however, clothing and hair can trap vapor.
  • Link to prehospital management section

Route of Exposure

  • Inhalation - nerve agents are readily absorbed from the respiratory tract. Runny nose and tightness in the throat or chest begin within seconds to minutes after exposure. Nerve agent vapors are heavier than air. Odor does not provide adequate warning of detection.
  • Skin/Eye Contact - nerve agent liquids are readily absorbed from the skin and eyes. Vapors are not absorbed through the skin except at very high concentrations. Ocular effects may result from both direct contact and systemic absorption. The nature and timing of symptoms following dermal contact with liquid nerve agents depend on exposure dose; effects may be delayed for several hours.
  • Ingestion - ingestion of nerve agents is expected to be relatively rare compared to inhalation exposure or skin contact; however, they are readily absorbed from the GI tract and are highly toxic.

Clinical Signs and Symptoms

Nerve agents are potent acetylcholinesterase inhibitors causing the same signs and symptoms regardless of the exposure route. However, the initial effects depend on the dose and route of exposure.

  • Children are much more vulnerable than adults to nerve agent toxicity.
  • Manifestations of nerve agent exposure include:
    • Neuromuscular - pinpoint pupils (highly indicative of nerve agent exposure in a mass casualty situation), muscle twitching, confusion, seizures, flaccid paralysis, and coma.
    • In many instances children present with only neurological signs and symptoms.
    • Pulmonary - chest tightness, wheezing, shortness of breath, respiratory failure.
    • Gastrointestinal - nausea, vomiting, abdominal cramps, involuntary defecation.
    • Other - runny nose, excessive salivation and sweating, and urination.
  • Link to Toxic Syndromes
  • Link to Primary and Secondary Survey

Differential Diagnosis

  • The diagnosis in a severely intoxicated individual is straightforward. The combination of miosis, copious secretions, bronchospasm, generalized muscle fasciculations, and seizures is characteristic.
  • Look carefully for miosis (if present will be helpful). Miosis may not be present initially following a low volatility nerve agent exposure.
  • A mild vapor exposure may mimic a child having allergic rhinitis/conjunctivitis.
  • A mild vapor exposure may present with only visual complaints such as narrowing of the visual field or a sense that everything is going dark.
  • GI symptoms by themselves could be confusing and they could be the only presenting signs.
  • Opioid abuse can include miosis, apnea, seizures, etc.
  • Link to Chemical Hazards Emergency Medical Management Intelligent Syndromes Tool (CHEMM-IST)


Acute Patient Care Guidelines References