Chemical weapons

Background

• Can be released via unintended means such as a spill from a damaged railroad tank car or industrial explosion as well as by intentional means as chemical weapons.

Pediatric considerations

• Higher metabolic rate and faster basal respiratory rate, causing more rapid and larger exposures
• Skin is thinner and more permeable
• Agents heavier than air have increased concentrations closer to the ground exposing children > adults

Types

Chemical weapons

• Blister chemical agents (Vesicants)
  • Lewisite (L)
  • Sulfur mustard (H)
  • Phosgene oxime (CX)
• Pulmonary chemical agents
  • Ammonia
  • Methyl isocyanate
  • Methyl bromide
  • Hydrochloric acid
  • Chlorine gas
  • Phosgene
  • Pepper spray
• Incendiary agents
  • Agent orange
  • White phosphorus
• Cyanide chemical weapon agents
  • Hydrocyanic acid
  • Formonitrile
  • Prussic acid
• Nerve Agents
  • Acetylcholinesterase inhibitors
  • Includes household and commercial pesticides (diazinon and parathion)
  • G-series (sarin, tabun, soman) and V-series (VX)
  • V-series high viscosity with oily consistency

Cyanide Agents (CN)

• AKA Hydrocyanic acid, Formonitrile, Prussic acid
• Mimics carbon monoxide poisoning
• Smell of bitter almonds but not all people can smell cyanide
• Absorbed through skin, inhaled or ingested
• Can affect individuals near fire with synthetic materials or plastics
• Can penetrate rubber and barrier fabrics

Pathophysiology

• Cyanide inhibits cytochrome oxidase on mitochondria
• Cells unable to use oxygen in bloodstream
• Cellular asphyxiation

Symptoms

• Symptoms can be delayed up to 60 minutes
• Symptoms dependent on concentration, form of cyanide, and route of exposure
• CNS and cardiovascular system most susceptible
• Initially hypertension and tachycardia progressing to bradycardia, hypotension, and arrhythmias late
• Anxiety, dizziness, headache, apnea, seizures, and coma

Management

• 100% oxygen and antidote therapy
• Sodium nitrite (IV) or amyl nitrite (inhaled) to displace cyanide from cytochrome oxidase
• Sodium thiosulfate: For conversion of cyanide to excretable thiosulfate
• Repeat sodium nitrite and sodium thiosulfate in 30min at half initial dose if needed
• Hydroxocobalamin (Vit B12a): makes CN water soluble and non-toxic
• Cyanide Antidote Kit: Amyl nitrite pearls, sodium nitrite (IV), sodium thiosulfate (IV)
• Cyanokit: Less toxic than cyanide antidote kit and shown effective in cardiac arrest

Nerve Agents

• Acetylcholinesterase inhibitors
• Includes household and commercial pesticides (diazinon and parathion)
• G-series (sarin, tabun, soman) and V-series (VX)
  • G-series are volatile non-persistent agents that evaporate quickly
  • V-series high viscosity with oily consistency
• Rapidly absorbed through skin, symptoms generally develop within 1 hour
• Vapors are heavier than air and tend to sink into low places
• Sarin used in Tokyo subway attack in 1995; 5,000 sought medical attention with 12 deaths.

Pathophysiology

• Inhibits acetylcholinesterase → excess acetylcholine at both nicotinic and muscarinic receptors

Symptoms

• DUMBELLS
  • D-Diarrhea, U-Urination, M-Miosis, B-Bronchorrhea/Bradycardia, E-Emesis, L-Lacrimation, S-Salivation/Seizures
• Cholinergic toxidrome Toxidromes

Management

• Nerve agents prolong succinylcholine's paralytic effect
• Atropine for bronchorrhea and bronchoconstriction
  • Start at 2-6mg, double the dose q5-30min until control of secretions (no max dose)
• Pralidoxime to restore function of acetylcholinesterase (given over approximately 30 minutes; rapid infusion can cause hypertension)
  • Give as soon as possible - must be given before "aging" occurs to be effective
• Benzodiazepines for seizures (standard AEDs may be ineffective)
• Mark 1 Nerve Agent antidote Kit (NAAK): 2 autoinjectors:
  • 2mg atropine
  • 600mg pralidoxime
• DuoDote Autoinjector: 2.1mg atropine, 600mg pralidoxime in one autoinjector

Differential Diagnosis

Mass casualty incident

• Radiation exposure (disaster)
• Dirty bomb
• Bioterrorism
• Chemical weapons
• Natural Disaster (e.g. Hurricane, Earthquake, Tornado, Tsunami, etc)
• Unintentional large-scale incident (e.g. building collapse, train derailment, etc)
• Major pandemic
• Explosions

Management

• Depends on specific agent used
• Regardless of agent, Decontamination and ABCs are of primary importance
  • Use appropriate personal protective equipment (PPE)
  • Decontamination (should take place pre-hospital or otherwise prior to entering the ED)
    • Remove all patient clothing
    • Brush off dry agent (e.g. powders), copiously irrigate skin of any liquid contaminant

See Also

• Toxicology (Main)
• Weapon of mass destruction
• Hazmat exposure

References

Authors

Alec Weir, Ross Donaldson, Michael Holtz, Daniel Ostermayer, Neil Young, Jonathan Warren