CBRN preparedness — decontamination, agent recognition, specific antidotes

Definition / Overview

CBRN incidents involve deliberate or accidental release of chemical, biological, radiological, or nuclear agents capable of causing mass casualties. The ED must be prepared to receive, identify, decontaminate, and treat affected patients while protecting staff and the broader hospital environment. In Australia and New Zealand, CBRN preparedness sits within the broader Emergency Operations Plan (EOP) framework mandated at jurisdictional level, with coordination between pre-hospital services, HAZMAT teams, state health departments, and the receiving hospital.

Key principles:

• Decontamination before entry into the clinical care area is non-negotiable for chemically or radiologically contaminated patients
• Early agent recognition drives antidote selection and isolation precautions
• Personal protective equipment (PPE) hierarchy protects staff without compromising care
• Mass casualty triage (START/SALT) runs concurrently with decontamination
• Australian Poisons Information Centre (13 11 26) provides 24-hour toxicological advice for chemical exposures; state radiation protection authorities provide radiological guidance

Pre-Hospital Decontamination Zones

Zone Structure

Three concentric zones are established at scene by fire service / HAZMAT, with overall scene command held by fire service in the acute phase:

• All patients exit the hot zone via a single patient transfer point
• Entry and exit control prevents spread of contamination between zones
• Non-ambulatory patients (litter casualties) are decontaminated within the warm zone before transfer to the cold zone treatment area
• Vehicles used in the hot zone are considered contaminated and removed from service until decontaminated
• Leather items (shoes, belts, holsters) used by first responders cannot be adequately decontaminated and must be discarded; organophosphates in particular adsorb to leather and can cause secondary exposure

Field Decontamination Principles

• Remove all clothing: eliminates up to 80% of surface contamination rapidly
• Irrigate skin and hair with large volumes of soap and water in the warm zone
• Decontamination is most effective within the first minute of exposure but is rarely achievable in that window; it remains beneficial when performed as soon as feasible
• Ambulatory patients self-decontaminate under supervision; non-ambulatory patients require assisted decontamination
• Hypochlorite (0.5% solution, i.e. 1:10 dilution of household bleach) is an alternative skin decontaminant for chemical agents, particularly organophosphates and mustard; it is avoided for biological agent decontamination due to harm potential
• Runoff water must be contained to prevent environmental contamination

Internal Hospital Decontamination

ED Decontamination Area

• Located externally to the clinical care area, usually at the ED ambulance entry or a designated external bay
• Ambulatory patients and lower-acuity stretcher patients are decontaminated outside the ED
• Decontamination area requires: waterproof flooring with contained drainage, privacy screens, climate protection for patients, appropriate lighting, and a PPE donning/doffing station adjacent
• Only one patient entry point into the ED after decontamination is verified

Hospital Decontamination Protocol

1. Patient arrives: security restricts all other ED entry points; only the decontamination area entry is active
2. Triage nurse (in Level C PPE minimum) performs rapid primary assessment at the entry point
3. Clothing and belongings are removed, double-bagged, and labelled; items are retained for forensic / public health investigation
4. Patients shower with soap and warm water; assisted if unable to self-decontaminate
5. Eyes irrigated with normal saline 0.9% after whole-body wash if ocular exposure suspected
6. Radiation survey meter (Geiger-Müller counter) used before and after decontamination for radiological incidents; repeat decontamination until levels return to background
7. Patients issued hospital gown and moved to triage area
8. Critical medical devices (infusion pumps, hearing aids, ostomy equipment) remain with the patient unless a high-risk chemical is confirmed; walkers and canes are cleaned with soap and water or dilute bleach and returned
9. Runoff water collected and assessed before discharge to drain; small volumes in clinical settings generally remain below legal discharge limits

Staff PPE Levels

• ED decontamination staff routinely operate in Level C as minimum
• PPE donning and doffing protocols must be rehearsed annually; the doffing sequence is the highest risk period for self-contamination

Agent Recognition

Nerve Agents (Organophosphates: Sarin, VX, Tabun, Soman)

Mechanism: Irreversible inhibition of acetylcholinesterase causing accumulation of acetylcholine at muscarinic and nicotinic receptors.

Clinical features: The toxidrome is cholinergic excess:

• Muscarinic (SLUDGE/DUMBELS): Salivation, lacrimation, urination, defaecation, GI cramping, emesis; bradycardia, bronchospasm, bronchorrhoea, miosis (pinpoint pupils: key sign)
• Nicotinic: Fasciculations, muscle weakness, paralysis, tachycardia (can mask bradycardia)
• CNS: Seizures, coma, respiratory failure

Miosis + bronchospasm + secretions + fasciculations = nerve agent until proven otherwise.

Sulfur Mustard (Vesicant)

Mechanism: Alkylating agent causing DNA crosslinking and inhibition of cellular enzymatic activity, producing delayed ischaemic necrosis.

Clinical features (onset typically 2-24 hours after exposure):

• Skin: erythema progressing to large fluid-filled blisters, ulceration
• Eyes: conjunctivitis, corneal ulceration, blepharospasm
• Airway: mucosal necrosis, haemoptysis, respiratory failure
• Bone marrow suppression with delayed presentation

Key feature: Patients are often asymptomatic immediately after exposure; do not rely on symptom absence to exclude mustard exposure. Decontamination must occur before symptoms manifest.

Anthrax (Bacillus anthracis: Biological)

Three forms:

• Inhalational anthrax is the weaponised concern; mediastinal widening on CXR is the radiological hallmark
• Person-to-person transmission does NOT occur; standard precautions are sufficient
• Spores are not decontaminated by standard methods; HAZMAT decontamination with sporicidal agents required for the environment
• Notification to public health authorities is mandatory and urgent

Radiation (Radiological / Nuclear)

Key distinction:

• Acute Radiation Syndrome (ARS): Dose-dependent syndrome after whole-body exposure: prodrome (nausea, vomiting within hours), latent phase, manifest illness (haematopoietic, GI, cardiovascular/CNS injury at increasing doses), recovery or death
• Prodrome onset time inversely correlates with dose: vomiting within 1 hour = dose likely $\geq 2\,\text{Gy}$, a red flag for severe ARS
• Survivors of radiation accidents rarely pose contamination risk to ED staff if appropriate precautions are used; Chernobyl remains the exception

Specific Antidotes

Nerve Agent Antidotes

Atropine

• Mechanism: Competitive muscarinic antagonist; reverses secretions, bronchospasm, bradycardia; does NOT treat nicotinic effects (weakness, fasciculations)
• Dose: 2-4 mg IV bolus initially; repeat every 5-10 minutes, doubling the dose each time if required; endpoint is drying of secretions (NOT heart rate or pupil size)
• In severe poisoning, doses of 20-100 mg may be required in the first hour
• Auto-injectors (ATNAA in military context): atropine 2 mg + pralidoxime 600 mg per device

Pralidoxime (2-PAM)

• Mechanism: Reactivates acetylcholinesterase by cleaving the organophosphate-enzyme bond before "ageing" occurs (irreversible bond maturation); treats nicotinic effects including paralysis
• Dose: 1-2 g IV over 15-30 minutes, then infusion at 200-500 mg/hr; initiate as early as possible
• Effectiveness diminishes rapidly after ageing: soman ages within minutes, sarin within hours, VX and most pesticides within 24-48 hours
• Pralidoxime must be co-administered with atropine; not used alone

Benzodiazepines

• Indication: Seizures secondary to nerve agent; diazepam 10 mg IV or midazolam 0.15 mg/kg IM/IV
• Phenytoin is not effective for organophosphate-induced seizures

Cyanide Antidote

Hydroxocobalamin

• Indication: Cyanide poisoning (hydrogen cyanide gas in fires, industrial exposure, deliberate release)
• Mechanism: Binds cyanide to form cyanocobalamin (vitamin B12), which is renally excreted
• Dose: 5 g IV (70 mg/kg in children) over 15 minutes; repeat dose of 5 g if inadequate response; maximum 15 g
• Safe in the setting of smoke inhalation co-exposure with carbon monoxide (unlike dicobalt edetate)
• Turns urine and skin red/orange: warn staff this is expected and does not represent haemolysis

Radiological Antidotes / Blocking Agents

Potassium Iodide (KI)

• Indication: Nuclear reactor accident or detonation with radioiodine (iodine-131) release
• Mechanism: Saturates thyroid iodide uptake, preventing incorporation of radioactive iodine-131 and reducing thyroid cancer risk
• Dose (adult): 130 mg orally as a single dose; repeat daily if exposure continues
• Paediatric doses: 65 mg (3-12 years), 32.5 mg (1 month-3 years), 16 mg (neonates)
• Effective only against thyroid uptake of radioiodine; does NOT protect against other radiation types or isotopes
• Must be administered before or within 4 hours of exposure; benefit diminishes significantly after 8 hours
• Contraindications: thyroid disease (relative), iodine allergy (relative; risk-benefit must be weighed in mass-casualty nuclear event)

Prussian Blue (Insoluble)

• Indication: Internal contamination with caesium-137 or thallium
• Mechanism: Ion exchange resin in the GI tract that binds caesium and thallium, reducing enterohepatic recirculation and accelerating faecal elimination
• Dose: 3 g orally three times daily (adult); 1 g three times daily (children 2-12 years)
• Continue until bioassay indicates acceptable internal body burden
• Not useful for other radioisotopes; does not treat external irradiation

DTPA (Diethylenetriamine Pentaacetic Acid)

• Indication: Internal contamination with plutonium, americium, or curium
• Chelates transuranic elements, enhancing urinary excretion; administered IV or by inhalation
• Access via state radiation health authority or emergency stockpile

Complications and Special Considerations

Mass Casualty Triage in CBRN

• START triage (Simple Triage and Rapid Treatment) or SALT (Sort, Assess, Lifesaving Interventions, Treatment/Transport) is applied at the cold zone triage point
• Expectant (black tag): Patients requiring advanced resuscitation (CPR, prolonged airway management) in a resource-limited CBRN mass casualty are generally triaged expectant; CPR is not indicated when resources are overwhelmed
• Immediate (red): Airway compromise, uncontrolled haemorrhage, severe bronchospasm from nerve agents
• Triage category may change after decontamination; retriage all patients after decontamination is complete

Biological Agent Isolation

• Anthrax: Standard precautions only (no person-to-person spread); notify infection control and public health immediately
• Smallpox or viral haemorrhagic fever (VHF): Airborne + contact + eye protection; single-room negative pressure isolation; detailed contact tracing
• Post-exposure prophylaxis for anthrax: Ciprofloxacin 500 mg orally twice daily for 60 days (doxycycline 100 mg twice daily if ciprofloxacin not available); anthrax vaccine if available; coordinate with public health

Psychological and Operational Considerations

• "Worried well" patients will substantially outnumber genuinely contaminated patients; a separate assessment area away from the decontamination zone and treatment areas is required
• Hospital administrator or public information officer controls media access; a single coordinated message prevents conflicting public communications
• Annual decontamination drills are mandatory for ED staff; review of drill findings must be shared across the department
• State retrieval services must be notified early for inter-hospital transfers; retrieval teams require their own PPE and pre-notification of agent type
• Mandatory notification to state health department, police (forensic investigation), and public health unit applies to all deliberate CBRN events

Key Candidate Errors to Avoid

• Allowing a contaminated patient to bypass decontamination and enter the ED: this contaminates the resuscitation area and multiple staff
• Using atropine endpoint of heart rate or pupils rather than secretion drying in nerve agent toxicity
• Delaying pralidoxime: effectiveness is time-critical; do not wait for confirmation of specific agent before initiating treatment in a clear cholinergic toxidrome
• Giving hydroxocobalamin and sodium thiosulfate simultaneously: hydroxocobalamin is preferred; sodium thiosulfate may be used as an adjunct but is not first-line in cyanide poisoning from fire
• Failing to call the Australian Poisons Information Centre (13 11 26) for agent-specific guidance
• Omitting public health notification: mandatory and time-critical for all biological events and deliberate CBRN incidents
• Using Prussian blue for radioiodine (it is ineffective); potassium iodide is the correct agent for thyroid protection from radioiodine

Disposition

Sources

• ACEM policy documents
• ANZCOR / ARC Resuscitation Guidelines