Why does routine pulse oximetry fail to detect CO poisoning, and what test is required?
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Answer
COHb has absorption similar to oxyhemoglobin at the wavelengths the pulse-ox uses → falsely normal SpO₂. CO binds Hb with 200–250× affinity of O₂. Diagnosis requires co-oximetry. Treat with 100% O₂; HBO for severe/pregnant/neuro findings.
LO 2 · Lead Poisoning
Which two heme-synthesis enzymes does lead inhibit, and what classic peripheral-smear finding results?
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Answer
Lead inhibits δ-ALA dehydratase and ferrochelatase → microcytic sideroblastic anemia with basophilic stippling on smear. Chelate with succimer (oral, mild-mod) or EDTA + BAL (severe/encephalopathy). Also: burton's lines, wrist/foot drop, abdominal colic.
LO 3 · WARS History
What four history categories must be collected on EVERY poisoning patient?
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Answer
WARS:What (agent + ALL co-ingestants) · Amount + route · Route/Reason (accidental vs intentional vs recreational) · Since when (time of ingestion → drives decontamination window + APAP level timing).
LO 4 · Red-Flag Presentations
Name four vital-sign or exam findings that should immediately raise suspicion for occult poisoning.
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Answer
(1) Unexplained AMS / coma; (2) Seizure (especially first-ever, refractory, or in young adult); (3) Unexplained acidosis with ↑ anion gap; (4) Marked HR/BP abnormalities without cause. Also: pediatric arrhythmia, wide QRS, severe hypoglycemia, unique breath odor.
LO 5 · Labs
What is the universal "tox-screen quartet" ordered on every undifferentiated poisoning?
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Answer
APAP level, salicylate level, ECG, bedside glucose. Add: BMP (anion gap, osmolar gap), lactate, VBG, β-hCG in reproductive-age women. Urine drug screen is low-yield (misses synthetics, long windows) — do NOT let it replace clinical toxidrome assessment.
LO 6 · Charcoal
What is the dose of single-dose activated charcoal, and which five substance classes does it not bind?
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Answer
Dose: 1 g/kg PO (max ~50–100 g) within ~1 h of ingestion in an awake, airway-protected patient. LAME Ca exceptions (not adsorbed): Lithium · Alcohols · Metals (iron, lead) · Electrolytes · Caustics. Also poor: hydrocarbons, cyanide.
LO 6 · Decontamination
When is gastric lavage indicated, and when is it absolutely contraindicated?
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Answer
Consider only for life-threatening ingestion within 1 h when charcoal is ineffective (e.g., metals). Contraindicated: caustics (re-expose esophagus), hydrocarbons (aspiration pneumonitis), unprotected airway. Ipecac/lavage are no longer routine.
LO 7 · SLIME Mnemonic
Which five toxins are classically dialyzable, and why does digoxin escape the list?
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Answer
SLIME — Salicylates · Lithium · Isopropanol (and toxic alcohols: methanol, EG) · Metformin · Ethylene glycol. Digoxin has a huge Vd (~7 L/kg) and tissue distribution → not dialyzable; treat with digoxin-specific Fab.
LO 7 · MDAC
Which four agents benefit from multi-dose activated charcoal via enterohepatic / entero-enteric interruption?
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Answer
CPSA:Carbamazepine · Phenobarbital · Salicylates · Antidepressants (TCAs — controversial; dapsone, theophylline, quinine also classic). MDAC = 0.5 g/kg every 4–6 h. Requires intact bowel + airway.
LO 8 · Anticholinergic Toxidrome
Give the five-part mnemonic for anticholinergic toxidrome.
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Answer
"Hot as a hare, Dry as a bone, Red as a beet, Blind as a bat, Mad as a hatter." → hyperthermia, dry skin/mucosa, flushing, mydriasis, delirium. Plus: urinary retention, ↓ bowel sounds, tachycardia. Diphenhydramine, TCAs, atropine, Jimson weed.
LO 8 · Cholinergic Toxidrome
What are the muscarinic and nicotinic features of organophosphate poisoning?
What is the antidote for methanol/ethylene glycol poisoning, and what is its mechanism?
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Answer
Fomepizole (preferred) or ethanol — both competitively inhibit alcohol dehydrogenase preventing formation of the toxic metabolites (formic acid → retinal; oxalic acid → renal). Add HD, folate (methanol), thiamine + pyridoxine (EG).
LO 10 · INH
An overdose of isoniazid produces refractory seizures. What is the antidote and how is it dosed?
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Answer
Pyridoxine (vitamin B6) dosed gram-for-gram of INH ingested (or 5 g empiric). INH depletes pyridoxine → ↓ GABA synthesis → seizures refractory to benzos alone. Also corrects the lactic acidosis.
LO 10 · OP & 2-PAM
Why is pralidoxime (2-PAM) time-sensitive in organophosphate poisoning?
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Answer
OPs phosphorylate acetylcholinesterase. Over hours the bond "ages" to an irreversible state. 2-PAM reactivates AChE before aging. Give ASAP with atropine. Atropine treats muscarinic; 2-PAM treats nicotinic (muscle weakness, respiratory failure).
LO 11 · Supportive Care
Name the three pillars of supportive care that save more poisoning patients than any antidote.
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Answer
(1) Airway / ventilation (intubate for AMS, seizures, respiratory depression); (2) Hemodynamics — IVF → pressors (norepinephrine first-line for most); (3) Seizure & temp control — benzos first-line for tox seizures; aggressive cooling for sympathomimetic/anticholinergic hyperthermia.
LO 12 · Toxidrome Pearls
How do you differentiate anticholinergic from sympathomimetic toxidrome at the bedside?
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Answer
Both have tachycardia, HTN, mydriasis, hyperthermia, agitation. Key discriminators: anticholinergic = DRY skin + absent bowel sounds + urinary retention; sympathomimetic = DIAPHORETIC + hyperactive bowel sounds + normal bladder. Cocaine vs. diphenhydramine — feel the skin and listen.
FIB 1 · LO 2
The top single-substance fatality class on the NPDS is _____, followed by acetaminophen, opioids, and alcohols.
Hint: "S" in the SOAP mnemonic.
FIB 2 · LO 2
Carbon monoxide binds hemoglobin with approximately _____-fold greater affinity than oxygen, and requires a _____ to diagnose.
A range will be accepted; co-oximetry is the gold-standard machine.
FIB 3 · LO 2
Chronic lead exposure inhibits the enzymes _____ and _____ in the heme-synthesis pathway, producing a microcytic anemia with basophilic stippling.
First enzyme is early in the pathway; second is the final step.
FIB 4 · LO 6
Activated charcoal is dosed at _____ g/kg and does not bind the "LAME Ca" substances, which stands for lithium, alcohols, metals, electrolytes, and _____.
FIB 5 · LO 7
The classic dialyzable toxins (SLIME mnemonic) include salicylates, _____, isopropanol/toxic alcohols, metformin, and ethylene glycol.
Second "L" letter — think mood stabilizer.
FIB 6 · LO 9
APAP toxicity Phase _____ (hours 0–24) is characterized by nonspecific nausea and normal LFTs — the deceptive "well-appearing" window. Peak hepatotoxicity occurs in Phase _____.
FIB 7 · LO 10
The antidote for β-blocker overdose is _____, while calcium-channel blocker overdose is managed with calcium, _____-euglycemia therapy, and intravenous lipid emulsion.
β-blocker antidote is a pancreatic hormone. CCB adjunct uses high-dose of a common hormone.
FIB 8 · LO 10
Methanol and ethylene glycol toxicity are treated with _____, which competitively inhibits _____ dehydrogenase and prevents formation of toxic metabolites.
Drag the steps into the correct chronological order, then click "Check Order." Each drill reproduces a classic time-course progression Step 1 loves to test.
Classic poisoning exam traps. Decide True or False — each statement reflects a misconception Step 1 loves to test.
Trap 1 · LO 2
Cherry-red skin is a sensitive clinical sign of carbon-monoxide poisoning and should be used to rule it in at the bedside.
FALSE. Cherry-red skin is a late, insensitive, and usually post-mortem finding. CO poisoning most often presents with nonspecific headache/nausea/AMS — you must order a co-oximetry level. Don't wait for cherry-red; treat with 100% O₂ and HBO when indicated.
Trap 2 · LO 6
Syrup of ipecac is still recommended in the ED for pediatric ingestions within one hour of presentation.
FALSE.Ipecac is no longer recommended in any setting — delays charcoal, induces vomiting that risks aspiration, and is no longer manufactured. The AAP withdrew its endorsement in 2003. Gastric lavage is also no longer routine; activated charcoal is the decontamination of choice.
Trap 3 · LO 6
Activated charcoal is the preferred decontamination for a child who ingested a bottle of ferrous sulfate 30 minutes ago.
FALSE. Iron is one of the "LAME Ca" substances that charcoal does not adsorb (metals). Use whole-bowel irrigation with polyethylene glycol for GI decontamination, follow iron levels, and administer deferoxamine for severe toxicity.
Trap 4 · LO 6
Gastric lavage and activated charcoal are appropriate initial interventions for an intentional hydrocarbon (kerosene) ingestion.
FALSE. Hydrocarbons are high aspiration risk — emesis or lavage provokes chemical pneumonitis. Charcoal does not adsorb them and worsens aspiration risk. Treat with supportive care; intubate for respiratory failure; no routine decontamination.
Trap 5 · LO 10
Flumazenil is the first-line antidote for an unresponsive polysubstance overdose presumed to contain benzodiazepines and a tricyclic antidepressant.
FALSE. Flumazenil can precipitate benzodiazepine withdrawal seizures and, in TCA co-ingestion, unmask lethal TCA seizures by removing the GABAergic brake. Avoid flumazenil in undifferentiated poisonings and chronic benzo users. Supportive care + sodium bicarbonate for TCA QRS widening.
Trap 6 · LO 10
Physostigmine should be given empirically to a tricyclic-overdose patient with tachycardia and delirium because of the anticholinergic features.
FALSE.Physostigmine is contraindicated in TCA overdose — it can precipitate asystole and refractory seizures. Use physostigmine only for pure anticholinergic toxidrome (e.g., Jimson weed) with no QRS widening. TCA cardiotoxicity → IV sodium bicarbonate.
Trap 7 · LO 7
Hemodialysis effectively removes digoxin from an acutely overdosed patient due to the drug's small molecular size.
FALSE. Digoxin has an enormous volume of distribution (Vd ~7 L/kg) — almost entirely tissue-bound. HD cannot access it. Treat with digoxin-specific Fab fragments. Digoxin is NOT in the SLIME mnemonic.
Trap 8 · LO 12
Dilated pupils (mydriasis) make an opioid overdose extremely unlikely and should redirect the differential.
TRUE (mostly). Classic opioid toxidrome = miosis + respiratory depression + ↓ LOC. Mydriasis points away from opioids toward anticholinergic/sympathomimetic. Exceptions: meperidine, propoxyphene, and tramadol can produce normal or dilated pupils; post-anoxic injury from any opioid overdose will also dilate pupils. Still: pinpoint pupils is the classic test.