The reader is strongly advised to supplement material in this chapter with the Medical Management Of Chemical Casualties Handbook, 3rd ed., 2000, USAMRICD, Aberdeen Proving Ground, MD.
Avoid becoming a casualty.
Protect yourself and instruct your personnel to do the same.
• Prevent further injury of the casualty by instructing him to put on the protective mask and mission-oriented protective posture (MOPP) ensemble, and administer self-aid. If contaminated, tell the individual to remove clothing and decontaminate potentially exposed body surfaces.
• Provide buddy aid by masking the individual, administering antidotes, and spot decontaminating exposed body areas.
• Ensure completeness of decontamination process to the greatest extent possible at the collocated patient decontamination station.
Potential for vapor exposure from an off-gassing residual agent or inadvertent contact with undetected liquid is a hazard for medical personnel.
Avoid contamination of the medical treatment facility (MTF).
Initial Treatment Priorities
• There is no single “best” way to prioritize emergency treatment for chemical or mixed casualties, although respiratory insufficiency and circulatory shock should be treated first. One workable sequence is shown below.
1. Treat respiratory insufficiency (airway management) and control massive hemorrhage.
2. Administer chemical agent antidotes.
3. Decontaminate the face (and protective mask if donned).
4. Remove contaminated clothing and decontaminate potentially contaminated skin.
5. Render emergency care for shock, wounds, and open fractures.
6. Administer supportive medical care as resources permit.
7. Transport the stabilized patient to a contamination-free (ie, clean) area.
Specific Chemical Warfare (CW) Agents and Treatment Considerations
Nerve Agents (GA, GB, GD, GF and VX)
General: Nerve agents are among the most toxic of the known chemical agents. They pose a hazard in both vapor and liquid states, and can cause death in minutes by respiratory obstruction and cardiac failure.
Mechanism of action: Nerve agents are organophosphates that bind with available acetylcholinesterase, permitting a paralyzing accumulation of acetylcholine at the myoneural junction.
Signs/symptoms: Miosis, rhinorrhea, difficulty breathing, loss of consciousness, apnea, seizures, paralysis, and copious secretions.
Treatment: Each deployed US service member has three MARK I kits or Antidote Treatment-Nerve Agent Autoinjectors (ATNAAs) for IM self-injection in a pocket of the protective mask carrier; each kit delivers 2 mg injections of atropine sulfate and 600 mg pralidoxime chloride (2-PAMCl). Each US service member also carries a 10 mg diazepam autoinjector to be administered by a buddy.
Immediate IM or IV injection with
Atropine to block muscarinic cholinergic receptors (may require multiple doses in much greater amounts than recommended by Advanced Cardiac Life Support [ACLS] doses).
2-PAM (if given soon after exposure) to reactivate cholinesterase.
• Pretreatment: Military personnel may have also received pretreatment prior to nerve agent exposure. In the late 1990s, the US military fielded pyridostigmine bromide (PB tablets) as a pretreatment for nerve agent exposure (this reversibly binds to the enzyme acetyl cholinesterase, enhancing the efficacy of atropine against Soman).
Vesicants (HD, H, HN, L, and CX)
• General: The vesicants (blister agents) are cytotoxic alkylating compounds, exemplified by the mixture of compounds collectively known as “mustard.” Sulphur mustard is designated “HD” or “H”; nitrogen mustard is designated as “HN”; Lewisite is designated as “L”; and phosgene oxime is designated as “CX”.
• Mechanism of action: Mustard is an alkylating agent that denatures DNA, producing a radiomimetic effect, produces liquefaction necrosis of the epidermis, severe conjunctivitis, and if inhaled, injures the laryngeal and tracheobronchial mucosa.
• Signs/symptoms: Skin blisters, moderate-to-severe airway injury (presentation can be delayed), conjunctivitis of varying severity that causes the casualty to believe he has been blinded, and mucus membrane burns. No delay with Lewisite: immediate burning of the skin and eyes.
• Treatment: Preventive and supportive. Immediate decontamination of the casualty has top priority. Agent droplets should be removed as expeditiously as possible by blotting with the M-291 kit, or flushing with water or 0.5% hypochlorite. The M-291 kit is extremely effective at inactivating mustard. Most military forces carry a decontamination powder or liquid that should be used immediately to remove the vesicant. Because mustard tends to be an oily solution, water may spread the agent. Dimercaprol is used by some nations in the treatment of Lewisite. Dimercaprol must be used with caution because the drug itself may be toxic.
Lung Damaging (Choking) Agents (Phosgene [CG], Diphosgene [DP], Chloropicrin [PS], and Chlorine)
General: Lung damaging or choking agents produce pronounced irritation of the upper and the lower respiratory tracts. Phosgene smells like freshly mowed hay or grass.
Mechanism of action: Phosgene is absorbed almost exclusively by inhalation. Most of the agent is not systemically distributed but rather is consumed by reactions occurring at the alveolar-capillary membrane.
Signs/symptoms: Phosgene exposure results in pulmonary edema following a clinically latent period that varies, depending on the intensity of exposure. Immediate eye, nose, and throat irritations may be the first symptoms evident after exposure (choking, coughing, tightness in the chest, and lacrimation). Over the next 2–24 hours the patient may develop noncardiogenic fatal pulmonary edema.
Terminate exposure, force rest, manage airway secretions, O2, consider steroids.
Triage considerations for patients seen within 12 hours after exposure.
Immediate care in ICU if available for patients in pulmonary edema.
Delayed: dyspnea without objective signs of pulmonary edema, reassess hourly.
Minimal: asymptomatic patient with known exposure.
Expectant: patient presents with cyanosis, pulmonary edema, and hypotension. Patients presenting with these symptoms within 6 hours of exposure will not likely survive.
The Cyanogens (Blood Agents AC and CK)
General: Hydrogen cyanide (AC) and cyanogen chloride (CK) form highly stable complexes with metalloporphyrins such as cytochrome oxidase. The term “blood agent” is an antiquated term used at a time when it was not understood that the effect occurs mostly outside the bloodstream.
Mechanism of action: Cyanide acts by combining with cytochrome oxidase, blocking the electron transport system. As a result, aerobic cellular metabolism comes to a halt.
• Signs/symptoms: Seizures, cardiac arrest, and respiratory arrest.
Immediate removal of casualties from contaminated atmosphere prevents further inhalation.
If cyanide was ingested, perform GI lavage and administer activated charcoal. Administer sodium nitrite (10 mL of 3% solution IV) over a period of 3 minutes, followed by sodium thiosulfate (50 mL of 25% solution IV) over a 10-minute period. The sodium nitrite produces methemoglobin that attracts the cyanide; the sodium thiosulfate solution combines with the cyanide to form thiocyanate, which is excreted.
Incapacitation Agents (BZ and Indoles)
• General: Heterogeneous group of chemical agents related to atropine, scopolamine, and hyoscyamine that produces temporary disabling conditions with potent CNS effects that seriously impair normal function, but do not endanger life or cause permanent tissue damage.
• Signs/symptoms: Mydriasis, dry mouth, dry skin, increased reflexes, hallucinations, and impaired memory.
Immediate removal of firearms and other weapons to ensure safety.
Physostigmine, 2–3 mg IM every 15 minutes to 1 hour until desired level is attained; maintain with 2–4 mg IV every 1–2 hours for severe cases.
• Thickened agents are chemical agents that have been mixed with another substance to increase their persistency (persistent agents may remain in the environment over 24 h).
• Casualties with thickened nerve agents in wounds are unlikely to survive to reach surgery.
• Thickened mustard has delayed systemic toxicity and can persist in wounds, even when large fragments of cloth have been removed.
Surgical Treatment of Chemical Casualties
The initial management of a casualty contaminated by chemical agents will require removal of MOPP gear as well as initial skin and wound decontamination with 0.5% hypochlorite before treatment.
Bandages are removed, wounds are flushed, and bandages replaced.
Tourniquets are replaced with clean tourniquets after decontamination.
Splints are thoroughly decontaminated.
Only the vesicants and nerve agents present a hazard from wound contamination. Cyanogens are so volatile that it is extremely unlikely they would remain in a wound.
The risk of vapor off-gassing from chemically contaminated fragments and cloth in wounds is very low and insignificant.
Off-gassing from a wound during surgical exploration will be negligible or zero.
Use of Hypochlorite Solution
Household bleach is 5% sodium hypochlorite, hence, mix 1 part bleach with 9 parts water to create ~ 0.5% solution.
Dilute hypochlorite (0.5%) is an effective skin decontaminant, but the solution is contraindicated for use in or on a number of anatomical areas:
Eye: may cause corneal injuries.
Brain and spinal cord injuries.
Peritoneal cavity: may lead to adhesions.
Thoracic cavity: hazard is still unknown although it may be less of a problem.
Full strength 5% hypochlorite is used to decontaminate instruments, clothing, sheets, and other inanimate objects.
Wound Exploration and Debridement
Surgeons and assistants should wear well-fitting, thin, butyl rubber gloves or double latex surgical gloves. Gloves should be changed often while ascertaining that there are no foreign bodies or thickened agents remaining in the wound.
Wound excision and debridement should be conducted using a no-touch technique. Removed fragments of tissue should be dumped into a container of 5% hypochlorite solution. Superficial wounds should be wiped thoroughly with a 0.5% hypochlorite and then irrigated with copious amounts of normal saline.
Following the Surgical Procedure
• Surgical and other instruments that come into contact with possible contamination should be placed in 5% hypochlorite for 10 minutes prior to normal cleansing and sterilization.
• Reusable linen should be checked with the chemical agent monitor (CAM), M8 paper, or M9 tape for contamination. Soak contaminated linen in 5% hypochlorite.