Chemical and Biological Agents, Toxic Terrorism, and Hazardous Materials
Chemical agents
Nerve agents (sarin, soman, VX) are organophosphates: cholinergic crisis with miosis, secretions, sweating, fasciculations, and seizures. Treat with atropine titrated to secretions, an oxime, and benzodiazepines for seizures; protect rescuers with Level A or B PPE and SCBA. Mustard agents cause delayed blistering, ocular injury, and airway burns with no antidote - supportive care and decontamination. Lewisite can be treated with dimercaprol. Blood agents include cyanide (hydroxocobalamin) and arsine (hemolysis). Choking agents such as chlorine and phosgene cause pulmonary edema after a latent period. Incapacitating agents (aerosolized fentanyl, BZ) are managed supportively.
Biological agents
Anthrax: gram-positive rods, spores, mediastinal widening; treat with ciprofloxacin or doxycycline plus antitoxin for systemic disease, and provide postexposure prophylaxis with antibiotics and vaccine. Plague, tularemia, brucellosis, Q fever, smallpox, botulism (descending paralysis, antitoxin), ricin, and viral hemorrhagic fevers are Category A/B concerns. Recognize epidemiologic clues: unusual organism, unusual resistance, unusual location, and a point-source epidemic curve.
Hazmat operations
Respect hot, warm, and cold zones. Level A is fully encapsulating with SCBA; Level D is street clothing. Decontaminate before transport to prevent secondary contamination, and establish incident command early.
Radiation
ALARA - time, distance, shielding. Potassium iodide blocks thyroid uptake of radioiodine only; Prussian blue is used for cesium and DTPA for actinides.
Traps
Do not enter the hot zone to rescue; rescuer safety precedes patient care. Vapor-induced miosis alone does not require atropine if systemic secretions are absent.
Worked example
Multiple patients with pinpoint pupils, secretions, and seizures after a subway release: atropine, oxime, benzodiazepines, and full decontamination before transport.
Analytical Toxicology, Antidotes, and Forensic Toxicology
Bedside and laboratory analysis
Calculate the anion gap (Na − [Cl + HCO3]) and the osmolar gap (measured − calculated osmolality, where calculated = 2Na + glucose/18 + BUN/2.8). An elevated osmolar gap suggests unmeasured osmoles early (methanol, ethylene glycol, isopropanol, mannitol), but it normalizes as metabolism proceeds, so a normal value never excludes toxic alcohol ingestion. Urine pH and ion trapping guide alkalinization. Co-oximetry distinguishes carboxyhemoglobin and methemoglobin, which standard pulse oximetry misses. Cholinesterase activity supports organophosphate diagnosis, but treatment is clinical.
Screening tests
Immunoassay urine drug screens are qualitative and prone to false positives (amphetamines with pseudoephedrine, bupropion, or ranitidine; opioids with poppy seeds; PCP with ketamine or dextromethorphan) and false negatives (fentanyl, synthetic cannabinoids). Confirmatory GC-MS or LC-MS is required for legal or forensic purposes. Never withhold treatment because of a screen result.
Antidote principles
Match antidote to mechanism and severity; supportive care remains the mainstay. Core pairs include naloxone, flumazenil (risky), glucagon, calcium, sodium bicarbonate, N-acetylcysteine, fomepizole, hydroxocobalamin, methylene blue, deferoxamine, pralidoxime, atropine, physostigmine, digoxin Fab, lipid emulsion, octreotide, pyridoxine, and Prussian blue.
Forensic toxicology
Maintain chain of custody from collection through reporting. Understand postmortem redistribution, site-dependent blood concentrations (femoral preferred), vitreous and hair testing, ethanol back-extrapolation (Widmark principle, ~15–20 mg/dL/hour), and the difference between therapeutic, toxic, and fatal concentrations.
Traps
A negative screen or a therapeutic level does not exclude poisoning; timing, chronicity, and tolerance determine effect.
Worked example
An unconscious patient with an undetectable urine screen after suspected fentanyl exposure: treat clinically with naloxone and observation, not according to the screening result.