Chemical weapons

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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

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
  • Prophylaxis in the military, high risk setting with pyridostigmine
    • Reversibly bind acetylcholinesterase before exposure to nerve agents
    • Pyridostigmine 30 mg PO q8[1]

Differential Diagnosis

Mass casualty incident

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

References

  1. Dunn MA, Sidell FR. Progress in medical defense against nerve agents. JAMA. 1989;262:649–652.