Emergency Preparedness 17:
Chemical Agents Portal
Chemical detection can be problematic.1 Urban, pre-hospital response now includes Metropolitan Medical Strike Response System (MMRS) teams that may detect a chemical threat prior to victim arrival. Rural centers won’t have this luxury but can learn what to adapt to their circumstances by monitoring emerging literature from this source. Recognition of a large-scale chemical attack is generally straightforward once multiple victims present with rapidly developing, similar symptoms. A huge challenge for civilian health care facilities is the ability to handle the direct presentation of large numbers of contaminated patients with the unique risk of secondary contamination. The rural facility needs to proactively address needs such as:
Community-based planning;
Integrated incident management systems;
Personnel training for undifferentiated chemical attacks;
Decontamination facilities and protocols;
Protective equipment and stocks of necessary medicines; and
Access to experts.
Current chemical agents of concern primarily attack nerves, skin, lungs, or blood. The nerve and skin agents are more likely to be used. Categories include:
Nervous system—peripheral and central effects. Examples are sarin (German agent B or GB) and VX (a V agent).
Skin—blistering (vesicant) effects. An example is mustard.
Lungs—inflammatory effects. Examples are phosgene and chlorine.
Blood—oxygen-blocking effects. An example is cyanide.
Nerve agents
Sarin
and VX are organophosphates. Very small doses may be lethal. Sarin is a
liquid but primarily poses a vapor threat due to its high volatility,
with inhalation being the main mode of exposure. VX is a liquid threat
with skin exposure being the main concern. Exposure causes
acetylcholinesterase, which degrades acetylcholine, to be inhibited,
allowing acetylcholine (the body’s main neurotransmitter) to over
accumulate at the neuronal synapses. This excess acetylcholine proceeds
to overstimulate muscarinic and nicotinic receptors, which causes the
following effects:
Central effects: seizures, coma, apnea
Peripheral muscarinic effects: bronchorrhea, bronchoconstriction, vomiting, defecation, salivation, lacrimation, rhinorrhea, and miosis. The major threat is from pulmonary compromise.
Peripheral nicotinic effects: muscle fasciculations, flaccid paralysis, hypertension, tachycardia
Diagnosis, decontamination, and treatment are based on history and clinical findings. RBC cholinesterase levels can confirm the diagnosis after the fact. Symptoms can range from mild to severe. Symptoms from vapor exposure appear rapidly, and there are no delayed effects; so patients who are asymptomatic after an hour or so have not been exposed to vapors. On the other hand, although liquid exposure can cause death rapidly, there can be delayed effects and these potential victims need observation for 18 hours or so after precautionary decontamination.
Treatment
and decontamination may need to occur simultaneously. Prevention of
health care worker exposure during care delivery is of utmost
importance and involves protective suits.2 Decontamination for sarin
vapor exposure is a matter of removing the exposed clothes. Liquid
exposure decontamination consists of clothing removal and showering.
Three drugs (given IM or IV) are used to combat organophosphate effects:
Atropine for the muscarinic effects: 2 to 6 mg IV depending on severity, with 2 mg repeated every 5 to 10 min as needed until secretions are dry. Give atropine before needed intubation if possible. PEDS: 0.02 mg/kg IV (minimal dose 0.1 mg) with repeated doses every 5 to 10 min as needed until secretions are dry.
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Pralidoxime chloride (2-PAM) for nicotinic effects: 1 g IV over 30 min; may repeat every hour as needed. PEDS: 15 mg/kg IV over 30 min. 2-PAM may cause hypertension that requires management with intravenous anti-hypertensives such as phentolamine. This requires close monitoring. See Vol II—Circ Skills 1 Arterial and Venous Catheter Insertion.
Benzodiazepams for seizure prevention and treatment: diazepam 5 to 10 mg IV with additional (usually smaller) amounts given as necessary; watch for respiratory depression. PEDS: 0.2 to 0.3 mg/kg IV; additional amounts prn.
See Vol III—TOX18 Organophosphates Toxicity.
Skin agents
Mustard
is a chemical that has both liquid and vapor activity and both local
(skin, eyes, and lungs) and systemic (bone marrow) toxicity. Vapor
exposure causes second-degree type burns; liquid may cause full
thickness burns. Mustard injures shortly after contact, there is no
antidote, and treatment consists of decontamination and supportive care
(such as airway maintenance).
Decontamination should be done as soon as possible; remove clothes and
wash/shower.
Standard burn wound management applies with the exception of fluid parameters. There is much less fluid loss. Avoid overhydration. See Vol III—ENV3 Burns Management.
Airway injury is dose dependent; match airway management to the degree of injury. See Vol I—PATHWAY 6 Adult Respiratory, PATHWAY 7 Pediatric Respiratory; Vol III—AIR1 Rapid Sequence Intubation.
Eyes need immediate irrigation with follow-up mydriatics, antibiotics, topical steroids, petroleum jelly (to prevent adhesions), and analgesia. Patients need to be monitored for bone marrow suppression (watch for falling WBC counts); death often occurs from secondary opportunistic infection(s).
Pulmonary agents
Chlorine
and phosgene are examples of gases that cause inflammatory reactions
upon exposure to eyes, upper airways, and lower airways. Bronchospasm
may result. Noncardiogenic pulmonary edema can occur in a delayed
fashion (4 to 6 hours or more). Treatment consists of decontamination
(mainly removal of clothes, eye irrigation prn, shower prn), assessment
of the extent of injury, supportive care of the eyes and airways, and
observation. No antidote exists. Steroids may or may not help.
See Vol I— PATHWAY 6 Adult Respiratory,
PATHWAY 7 Pediatric Respiratory;
Vol III—AIR1 Rapid Sequence Intubation.
In a mass casualty incident, limited resources such as ventilators,
could become critical barriers to adequate care delivery.
Blood agents
Cyanide
is an example of an agent that inhibits oxygen use at the cellular
level. Low-level exposure may produce non-specific symptoms such as
anxiety, headache, and dizziness. Tachypnea and/or vomiting may be
present. High-dose exposure can be quickly fatal, with patients
presenting with seizures, coma, shock, or in cardiac/respiratory
arrest. Mouth-to-mouth resuscitation should be avoided. Discard
clothing, give oxygen, and prepare to use cyanide antidote kit. See Vol
I—PATHWAY 1 Altered Level of Consciousness; Vol III—TRAU CARE 1 Shock,
TOX1 Systematic Approach, TOX16 Hyperbaric Oxygen and Normobaric Oxygen.
References
- Fatah AA et al. Guide for the selection of chemical agent and toxic industrial material detection equipment for emergency first responders. National Institute of Justice Guide. 2000.
- Arnold J, Lavonas E. CBRNE - Personal Protective Equipment. emedicine. Oct 16, 2001.