L 27 Toxidromes, Bites, Burns, and Anaphylaxis

Review Questions and Clinical Cases (Questions & Discussion)

Case 1: Acetaminophen Ingestion * Question: A $22$ -year-old presents $8$ hours after ingesting acetaminophen. She is asymptomatic. What is the next best step? * Answer: Measure the APAP level and use the nomogram (Rumack-Matthew). * Rationale: Early-phase acetaminophen toxicity is often asymptomatic. The Rumack-Matthew nomogram guides the need for N-acetylcysteine (NAC). Naloxone is an opioid antidote, dialysis is not first-line, and charcoal is only effective within <1 hour of ingestion.
Case 2: Acetaminophen Mechanism * Question: What causes liver injury in acetaminophen overdose? * Answer: $NAPQI$ accumulation. * Rationale: Acetaminophen is broken down into nontoxic metabolites. When the system is overwhelmed, it is metabolized into $NAPQI$ (toxic). $NAPQI$ is normally neutralized by glutathione; once glutathione is depleted, liver injury occurs. Treatment involves NAC to replenish glutathione.
Case 3: Tinnitus and Hyperventilation * Question: A patient presents with tinnitus and hyperventilation. What is the treatment? * Answer: Sodium bicarbonate infusion. * Rationale: These symptoms indicate Salicylate Toxicity. Sodium bicarbonate alkalinizes the serum and urine. Intubation should be avoided because it can lead to a loss of respiratory compensation.
Case 4: Severe Salicylate Toxicity * Question: A patient has a salicylate level >100\,mg/dL with altered mental status (AMS). Next step? * Answer: Dialysis. * Rationale: A level >100\,mg/dL is a specific indication for hemodialysis.
Case 5: Anticholinergic Symptoms * Question: Patient with dry skin, dilated pupils, and confusion. Treatment? * Answer: Physostigmine (selected cases). * Rationale: Symptoms describe Anticholinergic Toxicity. Supportive care and benzodiazepines are standard, but Physostigmine reverses central effects in severe delirium.
Case 6: Opioid Overdose * Question: Unresponsive patient with pinpoint pupils and a respiratory rate ( $RR$ ) of $6$ . Best treatment? * Answer: Naloxone. * Rationale: Naloxone reverses respiratory depression caused by opioids.
Case 7: Methanol Poisoning * Question: Patient with vision loss and Anion Gap ( $AG$ ) acidosis. Treatment? * Answer: Fomepizole. * Rationale: Methanol poisoning is blocked by fomepizole, which inhibits alcohol dehydrogenase. Ethanol is an older alternative. Dialysis may be used as an adjunct.
Case 8: Ethylene Glycol Toxicity * Question: Patient with renal failure and hypocalcemia. Treatment? * Answer: Fomepizole. * Rationale: Ethylene Glycol is metabolized into toxic products causing kidney failure. Fomepizole prevents this metabolism.
Case 9: Alcohol Withdrawal * Question: $48$ hours after the last drink, a patient presents with agitation, tachycardia, and fever. Treatment? * Answer: Benzodiazepines. * Rationale: Benzodiazepines (Diazepam or Lorazepam) are first-line for alcohol withdrawal and Delirium Tremens ( $DTs$ ). Thiamine (the "banana bag") should also be given.
Case 10: Serotonin Syndrome * Question: Patient with hyperreflexia, clonus, and fever. Treatment? * Answer: Stop the offending drug and provide benzodiazepines.
Case 11: Cat Bites * Question: Most appropriate treatment for a cat bite? * Answer: Amoxicillin-clavulanate. * Rationale: Cat bites are deep punctures often infected by Pasteurella multocida. Amoxicillin-clavulanate is the preferred prophylactic antibiotic.
Case 12: Human Bites * Question: Best management for a human bite? * Answer: Surgical washout ( $OR$ washout) and antibiotics.
Case 13: Burn Fluid Resuscitation * Question: A $70\,kg$ patient with $30\%$ Body Surface Area ( $BSA$ ) burn. Treatment? * Answer: $8400\,mL$ of Lactated Ringer's ( $LR$ ). * Rationale: Calculated using the Parkland formula: $4\,mL \times 70\,kg \times 30\% = 8400\,mL$ . Half is given in the first $8$ hours.
Case 14: Minor Burn Care * Question: What is appropriate for minor burns? * Answer: Cooling, cleaning, and covering (the "4 C's").
Case 15: Anaphylaxis Management * Question: Patient with hypotension and wheezing after food exposure. Treatment? * Answer: Epinephrine $IM$ . * Rationale: Epinephrine is the first-line life-saving treatment ( $0.3-0.5\,mg$ in the thigh).

General Approach to Suspected Poisoning

Initial Assessment: Determine if the patient is stable or unstable. Assess for Altered Mental Status ( $AMS$ ), drowsiness, or vomiting.
History Acquisition: * Identify the Substance: Name, strength, and formula (e.g., Extended Release/ $ER$ or Enteric coated). * Timing: When was the substance ingested? * Quantity: How much was taken? * Resources: Use Poison Control, Pill Identifiers, or specific apps. * Context: Assess for illicit drug use, chemical exposure, comorbidities (which affect absorption), and intentionality (self-harm risk).
Unstable Patients: * Secure the airway. Be aware of increased secretions (anticholinergics) or foreign bodies (pills) obstructing the airway. * Resuscitate: Address low Blood Pressure ( $BP$ ), tachycardia, and arrhythmias. Provide Cardiovascular support with ionotropes if needed. * Order Labs: Metabolic panels, acid-base status, and kidney/liver function tests.

Methods of Decontamination

Hemodialysis: Removes substances that are water-soluble, low molecular weight, and not protein-bound. * Targets: Ethylene glycol, salicylates, lithium, ethanol, isopropanol, and valproic acid.
Activated Charcoal: * Timing: Generally used within <1 hour of ingestion. * Mechanism: Binds toxins still in the stomach (e.g., Phenobarbital, Carbamazepine). * Caution: Airway must be intact; avoid if the patient is obtunded to prevent aspiration pneumonitis.
Whole Bowel Irrigation: * Agent: Polyethylene glycol administered via Nasogastric ( $NG$ ) tube. * Indications: Calcium Channel Blockers ( $CCB$ ), enteric-coated medications, or Iron ( $Fe+$ ). * Effect: A laxative effect that pushes substances through the system.
Gastric Lavage: Only used in life-threatening circumstances.
Ipecac: No longer recommended for inducing vomiting.
Physical Decontamination: "The solution to pollution is dilution." Use water for external chemical exposures, wounds, and skin cleaning.

Diagnostics and Physical Examination

Vital Signs: Monitor for fever (salicylates) and tachycardia (salicylates, anticholinergics, sympathomimetics).
HEENT: * Odor: Check for ethanol or menthol scents. * Pupils: Look for Mydriasis (dilation) or Miosis (constriction).
Neurological: Monitor for tremors or seizures.
Universal Testing Battery: * Glucose (finger stick). * $EKG$ . * $BMP$ + $LFT$ ( $CMP$ ). * Anion Gap and Osmolar Gap calculation. * Electrolytes ( $Mg$ , $Ca+$ ). * Alcohol level and $HcG$ (pregnancy test). * Acetaminophen ( $APAP$ ) and Salicylate levels. * Urine Toxicology screen.

Toxidrome Master Comparison

Feature	Opioid	Cholinergic	Anticholinergic	Sympathomimetic	Sedative (Benzo)
HR/BP	$\downarrow$	$\downarrow HR$	$\uparrow HR/BP$	$\uparrow HR/BP$	Normal
Pupils	Miosis (Pinpoint)	Miosis	Mydriasis (Dilated)	Mydriasis	Normal
Skin	Normal	Diaphoretic (Sweaty)	Dry	Diaphoretic	Normal
Mental Status	Depressed	Confused	Delirium ("Mad")	Agitated	Depressed
Key Clue	$\downarrow RR$	$SLUDGE$	Dry + Hot	Sweaty + Crazy	Normal vitals
Treatment	Naloxone	Atropine	Physostigmine	Benzos	Supportive

Mnemonic Anchors: * Opioids: "Low everything." * Anticholinergics: "Dry as a bone, hot as a hare, blind as a bat, mad as a hatter." * Cholinergics: " $SLUDGE$ / $DUMBBELLS$ ." * Sympathomimetics: "Cocaine = sweaty + crazy."

Specific Toxins: Acetaminophen (APAP)

Significance: Second most common cause of liver transplant.
Mechanism: Overwhelmed glutathione leads to $NAPQI$ accumulation and hepatotoxicity.
Dosing Limits: * Max Adult Dose: $4\,g/day$ ( $3000-3500\,mg$ ). * Max Child Dose: $15\,mg/kg$ every $6$ hours (Max $60\,mg/kg/day$ ). * Toxicity Threshold: Develops at $7.5-10\,g/day$ or $140\,mg/kg$ .
Progression: * Day 1: Often asymptomatic; possible nausea/vomiting. * Day 2: Right Upper Quadrant ( $RUQ$ ) pain, elevated transaminases, hypotension. * Day 3-4: Liver/renal failure, encephalopathy, $DIC$ , lactic acidosis, death. * Day 4 - 3 Weeks: Recovery possible if the liver settles.
Management: * Rumack-Matthew Nomogram: Used for acute, one-time ingestions. Level of $150\,μg/mL$ at hour $4$ indicates toxicity. Reliable between $4-18$ hours post-ingestion. * N-Acetylcysteine ( $NAC$ ): Prevents $NAPQI$ binding to the liver. Best if given <8 hours; reduces damage up to $24$ hours.

Specific Toxins: Salicylates (Aspirin)

Mechanism: Stimulates the cerebral medulla causing hyperventilation and respiratory alkalosis.
Symptoms: * Early ( $3-8$ hrs): Tinnitus, vertigo, nausea/vomiting, abdominal pain. * Late ( $6-18$ hrs): Fever, diaphoresis, $AMS$ , metabolic acidosis, increased lactate. * Severe ( $12-24$ hrs): Seizures, arrhythmias, coma.
Toxicity Levels: * Mild: $40-80\,mg/dL$ . * Moderate: $80-100\,mg/dL$ . * Severe: >100\,mg/dL (Direct indication for hemodialysis).
Management: * $D5$ + Sodium Bicarbonate ( $Na+$ bicarb) to alkalinize urine (target urine pH > 7.5). * Caution: DO NOT intubate unless airway failure is certain; losing compensatory hyperventilation causes rapid clinical decline.

Alcohols and Alcohol Withdrawal

Ethanol Levels and Symptoms: * $0-0.05\%$ : Relaxed, decreased motor control. * $0.05-0.1\%$ : Impaired judgment and coordination. * $0.1-0.2\%$ : Gait instability, behavior changes. * $0.2-0.4\%$ : Dysarthria, amnesia, diplopia, nystagmus. * >0.4\%: Respiratory depression, coma, death.
Withdrawal Timeline: * $6-36$ hrs: Minor symptoms (tremors, anxiety, tachycardia). * $6-48$ hrs: Seizures. * $12-48$ hrs: Hallucinations (visual, auditory, tactile) with normal vitals. * $48-96$ hrs: Delirium Tremens ( $DTs$ ) - characterized by fever, agitation, and unstable vitals.
Withdrawal Treatment: Benzodiazepines (Diazepam/Lorazepam) + Thiamine ( $100\,mg\,IV$ ) + Folate (the "Banana Bag").
Toxic Alcohols: * Methanol: Windshield fluid; metabolized to formic acid. Causes blindness ("Me see nothing") and $AG$ acidosis. Treated with Fomepizole. * Ethylene Glycol: Antifreeze; metabolized to oxalic acid. Causes kidney failure ("Engine failure"), hypocalcemia, and Calcium Oxalate crystals. Treated with Fomepizole.

Bites and Envenomation

General Care: Update Tetanus, copious irrigation (no $H_2O_2$ or alcohol), and loose suturing. Update Tetanus if >10 years (clean) or >5 years (contaminated).
Cat Bites: $80\%$ infection rate due to deep puncture. Pathogen: Pasteurella multocida. Treat with Amoxicillin-Clavulanate.
Dog Bites: Most common ( $60-90\%$ ). Polymicrobial. Treat with Amoxicillin-Clavulanate.
Human Bites: Often on hands ("fight bite"). Requires surgical ( $OR$ ) washout and antibiotics.
Spiders: * Brown Recluse: Violin pattern. Painless bite initially $rightarrow$ hemorrhagic blister $rightarrow$ necrosis. Supportive care. * Black Widow: Red hourglass. Painful bite $rightarrow$ muscle spasms and abdominal pain. Antivenom for severe cases.

Burn Management

Classification: * $1^{st}$ Degree: Epidermis, red, painful (sunburn). * $2^{nd}$ Degree: Dermis, blisters, very painful. * $3^{rd}$ Degree: Full thickness, white/black, painless at center (nerves killed).
Rule of 9s (Adult): * Head/Neck: $9\%$ . * Arms: $9\%$ each. * Legs: $18\%$ each. * Torso: $18\%$ front, $18\%$ back. * Perineum: $1\%$ .
Parkland Formula: $4\,mL \times kg \times \%BSA$ . * First half given over $8$ hours, second half over next $16$ hours.
The 4 C’s: Cooling (water/saline), Cleaning (mild soap), Covering (topical ointment, non-adherent dressing), Comfort (pain control).
Note: Systemic prophylactic antibiotics are NOT indicated for any burn.

Allergic Reactions, Anaphylaxis, and Angioedema

Anaphylaxis Criteria: involvement of $\ge 2$ body systems or hypotension after exposure.
Treatment: Epinephrine $IM$ ( $0.3-0.5\,mg$ ) is first-line. Adjuncts include antihistamines ( $H1$ and $H2$ blockers) and steroids.
Angioedema Types: * Histamine-mediated: Rapid onset, hives/itching present. Responds to Epinephrine and antihistamines. * Bradykinin-mediated: Delayed onset, associated with $ACE$ inhibitors or $C1$ inhibitor deficiency. No hives. Does NOT respond to antihistamines. Treat by removing cause or giving $C1$ inhibitor replacement.