Learning Objectives
Classify chemical agents into four major categories
Recognize the SLUDGEM mnemonic for nerve agent toxidrome
Administer appropriate antidotes for each agent category
Explain the "aging" phenomenon of nerve agent-enzyme binding
Differentiate between delayed (mustard) and immediate (lewisite) vesicants
Implement chemical decontamination protocols and PPE requirements
Chemical Agent Classification
| Category | Examples | Primary Target | Onset | Antidote Available? |
|---|---|---|---|---|
| Nerve Agents | Sarin (GB), VX, Tabun, Soman | Nervous system | Seconds-minutes | YES |
| Blister (Vesicants) | Sulfur Mustard (HD), Lewisite (L) | Skin, eyes, airways | Hours (delayed) | BAL for Lewisite only |
| Blood Agents | Hydrogen Cyanide (AC), Cyanogen Chloride | Cellular respiration | Seconds-minutes | YES |
| Pulmonary Agents | Phosgene, Chlorine, Ammonia | Lungs/airways | Hours (delayed edema) | NO - supportive only |
Nerve Agents
Mechanism of Action
Nerve agents inhibit acetylcholinesterase, causing accumulation of acetylcholine at nerve synapses. This leads to continuous nerve stimulation - a cholinergic crisis.
Sarin (GB)
- • Volatile - primarily inhalation hazard
- • Rapid onset (seconds to minutes)
- • Non-persistent (evaporates quickly)
- • Heavier than air - settles low
VX
- • Oily liquid - skin absorption
- • Slower onset (minutes to hours)
- • Persistent (remains on surfaces)
- • Most toxic nerve agent
SLUDGEM Mnemonic - Cholinergic Toxidrome
Salivation
Lacrimation
Urination
Defecation
GI Distress
Emesis
Miosis
Pinpoint Pupils = #1 Early Sign
Additional Signs: Muscle fasciculations, bronchospasm, bronchorrhea (copious secretions), bradycardia, seizures, respiratory arrest
Nerve Agent Antidote Triad
ATROPINE
Blocks muscarinic receptors - dries secretions, opens airways
Endpoint: Dry secretions (NOT pupil size)
Note: May need massive doses (100+ mg)
PRALIDOXIME (2-PAM)
Reactivates acetylcholinesterase if given BEFORE "aging"
Timing: Must give EARLY
Note: Ineffective after aging occurs
DIAZEPAM (Valium)
Controls seizures, prevents brain damage
Indication: Seizures or severe exposure
Note: Part of NAAK kit
Critical Concept: "Aging"
The nerve agent-enzyme bond undergoes a chemical change called "aging" that makes it irreversible. Once aging occurs, pralidoxime (2-PAM) is USELESS.
| Agent | Aging Time |
|---|---|
| Soman (GD) | 2-6 minutes (fastest!) |
| Sarin (GB) | 3-5 hours |
| VX | 24-48 hours |
| Tabun (GA) | ~14 hours |
Blister Agents (Vesicants)
Overview
Vesicants cause severe chemical burns and blistering of skin, eyes, and airways. They are alkylating agents that damage rapidly dividing cells. Effects are often DELAYED.
Sulfur Mustard (HD)
"Mustard gas" - actually an oily liquid with garlic/mustard odor
Symptoms appear 2-24 hours after exposure - patients feel fine initially!
- • Eyes: Conjunctivitis, corneal damage, temporary blindness
- • Skin: Erythema → blisters → deep burns
- • Respiratory: Airway necrosis, pseudomembrane formation
- • Bone marrow: Suppression (like radiation)
NO ANTIDOTE. Supportive care: copious irrigation, wound care, pain management, monitor for bone marrow suppression.
Lewisite (L)
Arsenical vesicant - contains arsenic; geranium-like odor
Unlike mustard, causes immediate burning pain on contact!
- • Immediate eye and skin pain
- • Gray discoloration of skin
- • Rapid blistering
- • Systemic arsenic toxicity: "Lewisite shock"
Dimercaprol - chelates arsenic. Give within minutes of exposure for best effect. Dose: 3-5 mg/kg IM every 4-6 hours.
Clinical Pearl: Mustard vs Lewisite
| Feature | Sulfur Mustard | Lewisite |
|---|---|---|
| Pain on contact | NO (delayed) | YES (immediate) |
| Symptom onset | 2-24 hours | Immediate |
| Odor | Garlic/mustard | Geranium |
| Antidote | NONE | BAL (dimercaprol) |
Blood Agents (Cyanides)
Mechanism of Action
Cyanide inhibits cytochrome oxidase in mitochondria, blocking cellular respiration. Cells cannot use oxygen even though blood oxygen levels are normal. This causes cellular hypoxia (histotoxic hypoxia).
Hydrogen Cyanide (AC)
Colorless gas with "bitter almond" odor (not everyone can smell it). Extremely rapid action - death in minutes with high exposure.
Cyanogen Chloride (CK)
Also causes pulmonary irritation. Combines cyanide toxicity with lung damage.
Clinical Signs
- •Rapid onset: Headache, confusion, seizures
- •Cherry-red skin (classic but unreliable)
- •Bitter almond odor on breath (40% can't detect)
- •Hyperpnea → respiratory failure
- •Seizures, coma, death
Venous blood appears bright red (arterialized) because cells cannot extract oxygen
Cyanide Antidotes
Preferred agent. Vitamin B12 precursor that binds cyanide. Dose: 5g IV over 15 min. Safe in smoke inhalation.
- • Amyl nitrite pearls (inhaled)
- • Sodium nitrite IV
- • Sodium thiosulfate IV
Caution: Nitrites cause methemoglobinemia
Pulmonary Agents (Choking Agents)
Mechanism of Action
Pulmonary agents cause damage to the respiratory tract, leading to pulmonary edema and respiratory failure. The damage may be DELAYED - patients may feel fine for hours before deteriorating.
Phosgene (CG)
Smells like "freshly mown hay"
- • Delayed pulmonary edema (2-24 hrs)
- • Minimal initial symptoms
- • "Feels fine, then dies"
- • WWI most common CW agent
Chlorine (Cl)
Pungent, irritating odor
- • Immediate irritation
- • Coughing, choking
- • Eye and throat burning
- • Industrial chemical - easy to obtain
Ammonia (NH3)
Sharp, pungent odor
- • Causes alkali burns
- • Upper airway damage
- • Pulmonary edema possible
- • Industrial chemical
CRITICAL: Phosgene "Time Bomb"
Patients exposed to phosgene may have minimal initial symptoms and appear well. Pulmonary edema develops 2-24 hours later. These patients need:
- • Observation for at least 24 hours
- • Serial chest X-rays
- • Activity restriction (exertion worsens outcome)
- • Supplemental oxygen PRN
Treatment: Supportive Care Only
There is NO ANTIDOTE for pulmonary agents. Management is entirely supportive:
- • Remove from exposure
- • Supplemental oxygen
- • Bronchodilators for bronchospasm
- • Positive pressure ventilation if needed
- • AVOID fluid overload
- • Steroids (controversial)
- • Eye irrigation for chlorine
- • Monitor for 24+ hours
Chemical Decontamination
Decontamination is LIFE-SAVING for chemical agents
Unlike biological agents (delayed presentation), chemical agents require IMMEDIATE decontamination. Failure to decontaminate can result in death.
Decontamination Priorities
Cut off, don't pull over head. Bag separately. This removes 80-90% of contamination.
Before adding water - some agents react with water
Large volumes of water. Soap and water wash. Eyes: minimum 15 minutes irrigation.
Timing is Critical
- • Nerve agents: Decontaminate within MINUTES
- • Blister agents: Decontaminate within 1-2 minutes for best outcome
- • For mustard, even delayed decontamination (4-6 hours) may reduce toxicity
PPE Requirements
WARNING: Standard Hospital PPE is INSUFFICIENT
A contaminated patient can off-gas chemical agent vapor, poisoning unprotected healthcare workers. Decontamination MUST occur BEFORE the patient enters the ED.
| PPE Level | Protection | When to Use |
|---|---|---|
| Level A | Fully encapsulated suit, SCBA | Hot zone entry, unknown agents, vapor hazard |
| Level B | Chemical-resistant suit, SCBA | Known agent, splash hazard, decontamination team |
| Level C | Chemical-resistant suit, APR | Known agent, air-purifying respirator adequate |
| Level D | Standard work uniform | AFTER decontamination only, no vapor hazard |
After Proper Decontamination
Once a patient has been properly decontaminated, standard hospital PPE (gown, gloves, surgical mask) is adequate. The patient no longer poses a vapor hazard to staff.
Key Takeaways
Nerve agents: SLUDGEM toxidrome, treat with Atropine + 2-PAM + Diazepam
Miosis (pinpoint pupils) is the most reliable early sign of nerve agent exposure
2-PAM must be given BEFORE "aging" occurs - timing is critical
Mustard: DELAYED symptoms (hours); Lewisite: IMMEDIATE pain + BAL antidote
Cyanide: Hydroxocobalamin (Cyanokit) is preferred antidote
Phosgene: Patient may appear fine, then develop fatal pulmonary edema hours later
Decontamination is LIFE-SAVING - must occur BEFORE patient enters ED
Standard hospital PPE is INSUFFICIENT for contaminated patients