Prehospital Academy Lesson 27.1
Toxicology: An Overview
This lesson provides a comprehensive overview of toxicology for EMTs, aligning with national EMS education standards. It emphasizes the critical thinking required to identify substances, determine differential diagnoses, and formulate treatment plans based on the anticipated clinical course. Understanding the principles of toxicology is crucial for managing patients exposed to poisonous or toxic substances, from common household items to industrial chemicals and illicit drugs.
Introduction to Toxicology
Toxicology is the study of poisons or toxic substances, their effects on the body, and the methods for their detection and treatment. Toxicologic emergencies represent a significant portion of EMS calls and can range from accidental ingestions in children to intentional overdoses in adults, or occupational exposures.
Key Competencies for EMS Providers:
Apply fundamental knowledge of epidemiology, pathophysiology, and assessment findings.
Formulate a field impression and implement a comprehensive treatment plan.
Recognize and manage specific poisonings (e.g., nerve agents, carbon monoxide).
Understand when and how to contact poison control centers.
Manage inhaled, ingested, injected, and absorbed poisons.
Recognize and manage alcohol intoxication/withdrawal and opiate toxidromes.
Routes of Exposure
Toxic substances can enter the body through several routes, influencing the onset, severity, and management of poisoning.
Ingestion: Through the mouth and digestive tract (e.g., medications, household cleaners, contaminated food). This is the most common route for accidental poisonings.
Inhalation: Breathing in toxic gases, fumes, or aerosols (e.g., carbon monoxide, smoke, industrial chemicals).
Injection: Directly into the bloodstream via needles (e.g., illicit drugs) or animal/insect bites/stings.
Absorption: Through intact skin or mucous membranes (e.g., pesticides, certain chemicals).
Toxidromes: Recognizing Patterns of Poisoning
A toxidrome is a constellation of signs and symptoms that consistently result from a specific toxic exposure. Recognizing toxidromes allows EMS providers to rapidly identify the class of poison and anticipate necessary interventions, even if the specific substance is unknown.
Cholinergic Toxidrome: Caused by agents that stimulate acetylcholine receptors (e.g., organophosphates, nerve agents).
Symptoms: SLUDGEM (Salivation, Lacrimation, Urination, Defecation, Gastrointestinal upset, Emesis, Miosis), bradycardia, bronchospasm, muscle fasciculations.
Anticholinergic Toxidrome: Caused by agents that block acetylcholine receptors (e.g., atropine, antihistamines, tricyclic antidepressants).
Symptoms: "Hot as a hare, blind as a bat, dry as a bone, red as a beet, mad as a hatter" (hyperthermia, mydriasis, dry skin/mucous membranes, flushed skin, altered mental status), tachycardia.
Sympathomimetic Toxidrome: Caused by agents that stimulate the sympathetic nervous system (e.g., cocaine, amphetamines, methamphetamine).
Symptoms: Tachycardia, hypertension, hyperthermia, dilated pupils (mydriasis), agitation, paranoia, diaphoresis.
Opioid Toxidrome: Caused by opioid medications (e.g., heroin, morphine, fentanyl).
Symptoms: Respiratory depression, pinpoint pupils (miosis), altered mental status (sedation, coma).
Sedative-Hypnotic Toxidrome: Caused by benzodiazepines, barbiturates, or alcohol.
Symptoms: Central nervous system depression (sedation, ataxia, slurred speech), respiratory depression (less severe than opioids), normal pupils.
General Prehospital Management Principles
Scene Safety: Always ensure the scene is safe for providers. Hazardous materials may require specialized teams.
ABCs: Secure airway, ensure adequate breathing (administer oxygen, assist ventilations if needed), and support circulation.
Decontamination: If the substance was absorbed or in contact with skin/clothing, initiate decontamination (e.g., remove contaminated clothing, brush off powders, irrigate skin/eyes).
History: Obtain as much information as possible about the substance, route, time of exposure, and quantity. Look for pill bottles, chemical containers, or clues on scene.
Poison Control: Contact poison control centers early for expert guidance (e.g., 1-800-222-1222 in the US).
Transport: Rapid transport to an appropriate medical facility capable of advanced toxicologic management.
Supportive Care: Treat symptoms as they arise (e.g., maintain body temperature, monitor cardiac rhythm).
Critical Thinking Questions
You are called to a patient with pinpoint pupils, slow shallow breathing, and is difficult to arouse. What toxidrome do you suspect, and what is your immediate priority intervention?
A patient has spilled an unknown chemical on their skin and is complaining of burning. What are your immediate actions regarding scene safety and patient management?
Why is it crucial for EMS providers to contact poison control centers early in a toxicologic emergency, even if the substance is identified?
Differentiate between the expected presentation of a cholinergic toxidrome and an anticholinergic toxidrome. What signs would help you distinguish between the two?
A patient is suspected of carbon monoxide poisoning. What is the primary mechanism of toxicity for carbon monoxide, and what is the definitive prehospital treatment?