Toxic Gases, Chemicals, and Toxic Alcohols Practice Questions

25 multiple-choice questions on Toxic gases, chemicals, and toxic alcohols for paramedic and EMT students, from Chapter 28 (Toxicology). Read each question, pick your answer, then tap Show answer to check it and read the explanation.

25 practice questions

1. Carbon monoxide causes tissue hypoxia mainly because it:

   1. A. Binds hemoglobin ~200 times more tightly than oxygen
   2. B. Blocks the enzyme cytochrome oxidase in all body cells
   3. C. Destroys red blood cells in the circulation
   4. D. Causes severe bronchospasm and airway swelling
   Show answer

   Answer: A. Binds hemoglobin ~200 times more tightly than oxygen

   CO occupies hemoglobin binding sites and shifts the oxygen curve to the left, so less oxygen is delivered. Cytochrome oxidase blockade is the main mechanism of cyanide.

2. A man treated with oxygen for carbon monoxide poisoning now feels normal and wants to refuse transport. A reason to encourage evaluation is that:

   1. A. CO levels rise again after oxygen
   2. B. Delayed brain effects can develop
   3. C. Symptoms will return within minutes
   4. D. Oxygen can cause a late lung injury
   Show answer

   Answer: B. Delayed brain effects can develop

   Delayed neurologic sequelae, such as memory loss, personality change, and movement problems, can appear days to weeks after significant CO poisoning even when the patient feels well; hyperbaric oxygen may lower that risk for selected patients. Carboxyhemoglobin does not rebound once he leaves the source. Brief high-flow oxygen does not cause a late lung injury.

3. A pack-a-day smoker with no symptoms is checked with a CO-oximeter after a call in a smoky bar. His SpCO is 7%. The best interpretation is:

   1. A. Within the range seen in smokers
   2. B. Severe CO poisoning needing hyperbaric care
   3. C. A false reading caused by nail polish
   4. D. Proof of cyanide poisoning as well
   Show answer

   Answer: A. Within the range seen in smokers

   Nonsmokers usually have carboxyhemoglobin under 3%, but smokers commonly run up to about 10%, so 7% without symptoms is consistent with smoking. The reading must be judged with symptoms and exposure, and noninvasive CO-oximetry has a margin of error. Hyperbaric oxygen is considered for much higher levels or serious findings. Cyanide cannot be measured by CO-oximetry.

4. Breathing 100% oxygen reduces the half-life of carboxyhemoglobin from about 4 to 5 hours to about:

   1. A. About 5 to 10 minutes
   2. B. 60 to 90 minutes
   3. C. 12 to 18 hours
   4. D. 2 to 3 days
   Show answer

   Answer: B. 60 to 90 minutes

   High-flow oxygen speeds CO elimination several-fold, and hyperbaric oxygen shortens it further to about 20 to 30 minutes.

5. Hyperbaric oxygen therapy for carbon monoxide poisoning is most often considered when the patient:

   1. A. Has a mild headache that resolved with oxygen
   2. B. Has a carboxyhemoglobin level under 5 percent
   3. C. Is pregnant, passed out, or has neuro deficits
   4. D. Is a smoker with chronic low-level CO exposure
   Show answer

   Answer: C. Is pregnant, passed out, or has neuro deficits

   Severe or high-risk exposures may benefit from hyperbaric oxygen to reduce delayed neurologic injury. Fetal hemoglobin binds CO tightly, so pregnancy lowers the threshold.

6. A woman has been eating ground apricot kernels as a 'natural cancer cure.' She collapses with seizures and severe metabolic acidosis. You should suspect:

   1. A. Organophosphate toxicity
   2. B. Botulinum toxin
   3. C. Aflatoxin liver injury
   4. D. Cyanide poisoning
   Show answer

   Answer: D. Cyanide poisoning

   Apricot, peach, and bitter almond kernels contain amygdalin, which the gut breaks down to cyanide; products sold as 'laetrile' or vitamin B17 have caused cyanide poisoning with collapse, seizures, and lactic acidosis. Organophosphates cause heavy secretions and small pupils. Botulism causes descending paralysis with a clear mind. Aflatoxin causes slow liver injury, not sudden collapse.

7. A firefighter pulled from a burning apartment is unconscious, hypotensive, and acidotic despite oxygen. In addition to CO, you should suspect:

   1. A. Cyanide from burning plastics
   2. B. Hydrogen sulfide from the sewer lines
   3. C. Organophosphates from stored pesticides
   4. D. Methanol from cleaning products
   Show answer

   Answer: A. Cyanide from burning plastics

   Smoke from plastics, foam, and fabrics contains hydrogen cyanide. Unexplained shock and coma in a smoke victim warrant hydroxocobalamin.

8. Several people drank homemade liquor that turned out to contain methanol. They felt only mildly drunk at first, then 18 hours later developed vomiting, rapid breathing, and blurred vision. The delay occurs because:

   1. A. The gut absorbs methanol very slowly
   2. B. Toxic metabolites take time to form
   3. C. An allergy to methanol develops later
   4. D. The eye takes hours to absorb the toxin
   Show answer

   Answer: B. Toxic metabolites take time to form

   Methanol itself is only mildly intoxicating; the liver slowly converts it to formic acid, which causes the acidosis and optic nerve injury, so symptoms often start 12 to 24 hours later, and even later if ethanol was drunk too. Methanol is absorbed quickly, not slowly. The delay is not an allergy, and the eye injury comes from the circulating metabolite.

9. A worker collapsed in a sewer, and a coworker who went in to help also collapsed. Rescuers noted a rotten egg smell that quickly disappeared. The likely gas is:

   1. A. Carbon monoxide
   2. B. Chlorine gas
   3. C. Hydrogen sulfide
   4. D. Anhydrous ammonia
   Show answer

   Answer: C. Hydrogen sulfide

   H2S smells like rotten eggs at low levels but paralyzes the sense of smell at high levels, so the odor fading is a danger sign. CO has no odor at all.

10. The key to rescuing patients from a confined space with a toxic gas is:

    1. A. Rapid entry by the first EMS crew to arrive
    2. B. Holding your breath while dragging the patient
    3. C. Wearing a surgical mask while you enter
    4. D. Entry only by trained rescuers with SCBA
    Show answer

    Answer: D. Entry only by trained rescuers with SCBA

    Many confined-space deaths are would-be rescuers. Only properly equipped teams with self-contained breathing apparatus should enter.

11. A 2-year-old may have swallowed drain cleaner but has no mouth burns and is not drooling. Regarding esophageal injury, you should explain that:

    1. A. It is ruled out by the absence of burns
    2. B. It is only possible if he vomits blood
    3. C. No mouth burns does not rule it out
    4. D. It can be excluded by giving a drink
    Show answer

    Answer: C. No mouth burns does not rule it out

    Caustic ingestions can injure the esophagus and stomach even when the lips and mouth look normal, so every suspected ingestion needs evaluation (often endoscopy). Drooling, refusal to swallow, vomiting, and stridor raise concern, but their absence does not exclude injury. Giving a drink to test swallowing is not a safe or reliable test.

12. For a patient who swallowed a caustic substance, you should NOT:

    1. A. Induce vomiting or try to neutralize it
    2. B. Assess the airway for swelling and stridor
    3. C. Bring the container to the hospital
    4. D. Transport promptly to the emergency department
    Show answer

    Answer: A. Induce vomiting or try to neutralize it

    Vomiting re-exposes the esophagus, and neutralization produces heat that worsens burns. Drooling, stridor, or voice change signal airway injury.

13. A 3-year-old drank lamp oil and is now coughing and grunting with SpO2 91%. The major risk from hydrocarbon ingestion is:

    1. A. Acute liver failure
    2. B. Aspiration pneumonitis
    3. C. Calcium oxalate kidney stones
    4. D. Severe hypoglycemia
    Show answer

    Answer: B. Aspiration pneumonitis

    Low-viscosity hydrocarbons are easily aspirated and spread across the lungs, causing chemical pneumonitis. Coughing after ingestion suggests aspiration has occurred.

14. Regarding activated charcoal for hydrocarbon ingestion, you should:

    1. A. Give it at once to prevent systemic absorption
    2. B. Give it along with ipecac to empty the stomach
    3. C. Give it only if the hydrocarbon was gasoline
    4. D. Withhold it; it binds poorly and causes vomiting
    Show answer

    Answer: D. Withhold it; it binds poorly and causes vomiting

    Charcoal binds hydrocarbons poorly, and vomiting increases the risk of aspiration. Supportive care with oxygen is the mainstay.

15. A man who drank windshield washer fluid is now complaining of blurred vision, describing it as 'like being in a snowstorm,' and is breathing fast. The toxin is most likely:

    1. A. Ethylene glycol
    2. B. Isopropyl alcohol
    3. C. Ethanol
    4. D. Methanol
    Show answer

    Answer: D. Methanol

    Methanol is metabolized to formic acid, which damages the optic nerve and causes severe acidosis. Ethylene glycol mainly injures the kidneys.

16. A patient who drank antifreeze is at greatest risk of:

    1. A. Blindness from optic nerve damage in hours
    2. B. Kidney failure from oxalate crystals
    3. C. Hemorrhagic stroke from hypertension
    4. D. Liver failure within the first hour
    Show answer

    Answer: B. Kidney failure from oxalate crystals

    Ethylene glycol is metabolized to oxalic acid, which forms crystals in the kidneys and binds calcium, causing hypocalcemia. Blindness is the signature of methanol.

17. Isopropyl alcohol ingestion differs from methanol and ethylene glycol because it causes:

    1. A. Ketosis without severe acidosis
    2. B. Blindness with severe metabolic acidosis
    3. C. Kidney stones with low calcium levels
    4. D. Seizures from rapidly dropping glucose
    Show answer

    Answer: A. Ketosis without severe acidosis

    Isopropyl alcohol is metabolized to acetone, which causes a fruity breath odor and CNS depression but not a large anion gap acidosis. Fomepizole is not needed.

18. A farmworker with organophosphate poisoning needs intubation. The team avoids succinylcholine mainly because in this patient it can:

    1. A. Fail to cause any paralysis
    2. B. Reverse the atropine's effect
    3. C. Cause prolonged paralysis
    4. D. Trigger severe hypoglycemia
    Show answer

    Answer: C. Cause prolonged paralysis

    Succinylcholine is broken down by plasma cholinesterase, which organophosphates inhibit, so its paralysis can last far longer than expected; a nondepolarizing agent such as rocuronium is preferred. Succinylcholine still causes paralysis, does not reverse atropine, and does not cause hypoglycemia.

19. A child broke a mercury thermometer, and a parent cleaned up the beads with a household vacuum. The main danger to the family is:

    1. A. Swallowing glass shards
    2. B. Inhaling mercury vapor
    3. C. Skin burns from the beads
    4. D. Mercury absorbed by the gut
    Show answer

    Answer: B. Inhaling mercury vapor

    Elemental mercury is poorly absorbed from the gut and skin, but it vaporizes, and vacuuming spreads and heats it, raising the vapor in the air; inhaled vapor is well absorbed and can injure the lungs and nervous system. Swallowed beads usually pass without harm, the beads do not burn the skin, and glass is a minor issue. The room should be ventilated and the spill handled by trained cleanup.

20. A man carrying several blocks of dry ice home in a closed car becomes dizzy, short of breath, and confused. The most likely cause is:

    1. A. Carbon dioxide displacing oxygen
    2. B. Carbon monoxide given off by the ice
    3. C. Chlorine gas released by the ice
    4. D. Frostbite of the upper airway
    Show answer

    Answer: A. Carbon dioxide displacing oxygen

    Dry ice is solid carbon dioxide; as it turns to gas in a closed space it displaces oxygen and raises CO2, causing headache, dizziness, dyspnea, and confusion. Move him to fresh air and give oxygen. Dry ice does not produce carbon monoxide or chlorine, and breathing the cold gas does not freeze the airway.

21. Before treating a patient covered in a liquid organophosphate pesticide, you must first:

    1. A. Start an IV line and give atropine at once
    2. B. Place him in your ambulance to warm him
    3. C. Intubate him to secure the airway early
    4. D. Don PPE and decontaminate the patient
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    Answer: D. Don PPE and decontaminate the patient

    Organophosphates are absorbed through skin, and contaminated clothing can poison the crew. Decontamination and PPE come before patient contact.

22. A 6-week-old fed formula mixed with water from a private rural well is cyanotic despite oxygen, and a blood sample looks chocolate-brown. The likely cause is:

    1. A. Lead in the old water pipes
    2. B. Bacteria in the formula
    3. C. Nitrates in the well water
    4. D. Fluoride in the water
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    Answer: C. Nitrates in the well water

    Wells near farm fields can have high nitrate levels; in young infants nitrates are converted to nitrites, which turn hemoglobin into methemoglobin and cause cyanosis that does not improve with oxygen ('blue baby syndrome'). Lead causes anemia and developmental harm, not acute cyanosis. Bacterial contamination causes infection. Fluoride does not cause methemoglobinemia.

23. A worker splashed with hydrofluoric acid has severe pain out of proportion to a minor-looking burn on his hand. After irrigation, the specific treatment is:

    1. A. Sodium bicarbonate cream
    2. B. Silver sulfadiazine cream
    3. C. Hydrocortisone ointment
    4. D. Calcium gluconate gel
    Show answer

    Answer: D. Calcium gluconate gel

    Fluoride binds calcium and magnesium, causing deep tissue damage and possibly fatal hypocalcemia. Calcium gluconate binds the fluoride; bicarbonate does not.

24. A patient exposed to chlorine gas in a pool equipment room is coughing with burning eyes and wheezing. Chlorine injures the airway by:

    1. A. Binding hemoglobin in place of oxygen
    2. B. Forming acids when it contacts moist tissue
    3. C. Blocking cellular use of oxygen
    4. D. Inhibiting acetylcholinesterase in synapses
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    Answer: B. Forming acids when it contacts moist tissue

    Water-soluble gases such as chlorine and ammonia form acids or bases on moist membranes, irritating the upper airway. Treat with oxygen, bronchodilators, and removal from exposure.

25. Exposure to a poorly water-soluble gas such as phosgene is dangerous because:

    1. A. Pulmonary edema may be delayed for hours
    2. B. It causes immediate severe upper airway burns
    3. C. It is easily smelled and quickly avoided
    4. D. Symptoms resolve completely once in fresh air
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    Answer: A. Pulmonary edema may be delayed for hours

    Poorly water-soluble gases such as phosgene reach the alveoli and cause delayed noncardiogenic pulmonary edema. Exposed patients need observation even when they look well.