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Difficulty: HardOccupational and Environmental Exposures

A 62-year-old male is brought to the emergency department by his coworkers after collapsing in an unventilated greenhouse where he was applying agricultural chemicals. He has a past medical history of chronic obstructive pulmonary disease (COPD) and heart failure with preserved ejection fraction. Upon arrival, the patient is lethargic and in severe respiratory distress. Vital signs are temperature 37.1°C (98.8°F), blood pressure 95/60 mm Hg, heart rate 48/min, and respiratory rate 28/min. Physical examination reveals profuse diaphoresis and bilateral miosis with pupils measuring 1 mm. Auscultation of the chest demonstrates diffuse expiratory wheezing and coarse crackles bilaterally, accompanied by copious, frothy oropharyngeal secretions. Intermittent twitching of the calf and thigh muscles is observed. An electrocardiogram shows sinus bradycardia without ischemic changes. Which of the following is the most appropriate initial pharmacological intervention for this patient's current condition?

  1. Intravenous atropineAnswer
  2. B
    Intravenous furosemide
  3. C
    Inhaled albuterol and intravenous methylprednisolone
  4. D
    Intravenous pralidoxime
  5. E
    Intravenous naloxone

Answer

The most appropriate initial pharmacological intervention is intravenous atropine.
The correct intervention is intravenous atropine. This patient's presentation of pinpoint pupils, severe bradycardia, profuse diaphoresis, diffuse wheezing, copious frothy secretions, and muscle fasciculations occurring after agricultural chemical exposure is the hallmark presentation of a severe cholinergic crisis due to organophosphate poisoning. Organophosphates inhibit acetylcholinesterase, leading to a massive accumulation of acetylcholine at both muscarinic and nicotinic receptors. The most immediate threats to life are the muscarinic effects on the pulmonary system: severe bronchoconstriction and bronchorrhea (the 'killer B's'). Atropine is a competitive muscarinic receptor antagonist that rapidly reverses these pulmonary effects and stabilizes the heart rate. It should be administered immediately and titrated until airway secretions clear. Only after initial stabilization with atropine should pralidoxime (which regenerates the acetylcholinesterase enzyme but works slowly and primarily at nicotinic sites) be administered.

Step-by-Step Solution

1
Identify the primary toxidrome from the physical exam findings.
The patient exhibits miosis, bradycardia, diaphoresis, copious oropharyngeal secretions, wheezing, and muscle fasciculations.
These findings represent a combination of muscarinic (DUMBELS) and nicotinic (fasciculations) overstimulation, classic for cholinergic toxicity.
2
Synthesize the clinical presentation with the environmental exposure history.
The acute onset of a severe cholinergic crisis after collapsing in a greenhouse where agricultural chemicals were being applied points definitively to organophosphate poisoning.
Organophosphates are commonly used as agricultural pesticides and cause irreversible inhibition of acetylcholinesterase.
3
Differentiate the acute presentation from the patient's underlying chronic conditions.
The respiratory distress is driven by bronchorrhea and bronchospasm from toxic exposure, not an exacerbation of his underlying COPD or heart failure with preserved ejection fraction.
Anchoring on the past medical history would fail to explain the pupillary, cardiac, and neuromuscular findings.
4
Determine the correct initial sequence of antidotal therapy for organophosphate poisoning.
Intravenous atropine must be administered immediately.
Atropine is a muscarinic antagonist that crosses the blood-brain barrier and quickly dries airway secretions and reverses bronchospasm, which are the most immediate life-threatening complications. Pralidoxime is given subsequently to regenerate the enzyme.

Key Concept

Organophosphate pesticide exposure causes irreversible acetylcholinesterase inhibition, leading to a cholinergic crisis that must be initially managed with intravenous atropine to reverse life-threatening muscarinic effects, prior to administering pralidoxime.
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Topics

Occupational and Environmental Exposures

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