Rosen & Barkin's 5-Minute Emergency Medicine Consult (493 page)

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Visual Loss

The author gratefully acknowledges Vinh D. Ngo’s contribution for the previous edition of this chapter
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CODES

• 377.30 Optic neuritis, unspecified
  
• 377.31 Optic papillitis
  
• 377.32 Retrobulbar neuritis (acute)
  

BASICS

• Organophosphates (pesticides and nerve agents) irreversibly bind and deactivate cholinesterases, including acetylcholinesterase
  
• Acetylcholine accumulates at neural synapses, causing central and peripheral cholinergic overdrive
  
• Predominant effects (muscarinic, nicotinic, CNS) may vary and can overlap.
  
• Mortality is secondary to respiratory failure:
  
  • Weakness of respiratory muscles
    
  • Bronchorrhea and bronchoconstriction
    
  • Central depression of respiratory drive
    

• Symptoms are difficult to differentiate in toddlers
  
• Common symptoms: Miosis, salivation, and muscle weakness
  
• Seizure activity in 25% of pediatric cases:
  
  • Only 3% in adults
    

• Exposure to insecticides (organophosphorus compounds)
  
• Exposure to chemical nerve agents (sarin, soman, tabun, VX)
  
• Extremely well absorbed from lung, GI tract, skin, mucosa, eyes
  

DIAGNOSIS

• Classic presentation: Cholinergic toxidrome:
  
  • DUMBELS:
    
    • D
      iarrhea/diaphoresis
      
    • U
      rination
      
    • M
      iosis/muscle fasciculations
      
    • B
      radycardia, bronchorrhea, bronchospasm
      
    • E
      mesis
      
    • L
      acrimation
      
    • S
      alivation
      
  • May have garlic odor
    
• Chronic intermittent exposure, nonspecific symptoms:
  
  • Weakness
    
  • Fatigue
    
  • Malaise
    
  • Anorexia
    
• Mild exposure:
  
  • CNS:
    
    • Headache
      
    • Dizziness
      
    • Tremors of tongue and eyelids
      
    • Weakness
      
  • GI:
    
    • Anorexia
      
• Moderate exposure:
  
  • CNS:
    
    • Muscle fasciculation then flaccid paralysis
      
    • Respiratory muscle weakness
      
    • Incoordination and ataxia
      
    • Agitation
      
    • Tremors
      
    • Confusion
      
  • Visual:
    
    • Pinpoint nonreactive pupils
      
  • Respiratory:
    
    • Respiratory muscle weakness
      
    • Bronchorrhea
      
  • Cardiovascular:
    
    • Bradycardia
      
  • GI:
    
    • Nausea/vomiting
      
    • Abdominal cramps
      
  • Exocrine glands:
    
    • Salivation
      
    • Lacrimation
      
• Severe exposure:
  
  • CNS:
    
    • Convulsions
      
    • Coma
      
    • Centrally mediated respiratory depression
      
  • Respiratory:
    
    • Bronchoconstriction
      
    • Wheezing
      
    • Dyspnea
      
    • Increased bronchial secretions
      
  • Cardiovascular:
    
    • Bradycardia (tachycardia may follow pulmonary edema and hypoxia)
      
    • Heart block
      
    • Cyanosis
      
  • GI:
    
    • Nausea, vomiting
      
    • Abdominal pain
      
    • Diarrhea, fecal incontinence
      
  • Exocrine glands:
    
    • Diaphoresis
      
    • Salivation
      
    • Lacrimation
      
  • Bladder:
    
    • Frequency
      
    • Urinary incontinence
      
    • Nicotinic manifestations
      

Inquire about possible exposure, occupation, recent insecticide at home, mislabeled, or poorly stored insecticides:

• Obtain original container if suicide attempt.
  
• Look for parasympathetic and CNS signs with muscle weakness or paralysis.
  

• RBC and plasma cholinesterase levels to confirm diagnosis:
  
  • RBC (true) cholinesterase level is best for synaptic inhibition (a send-out lab).
    
  • Plasma (pseudo)cholinesterase level not as reliable but more timely:
    
    • These are markers for poisoning
      
    • Depending on the agent and the patient, these levels may vary
      
  • Cholinesterase levels:
    
    • Latent exposure: >50% of normal value
      
    • Mild exposure: 20–50% of normal value
      
    • Moderate exposure: 10–20% of normal value
      
    • Severe exposure: <10% of normal value
      
  • Do not wait for cholinesterase results before administering treatment.
    
• CBC, electrolytes, glucose, BUN, creatinine
  
• ABG when respiratory symptoms are present
  

• CXR if respiratory difficulty is present or suspect pulmonary edema:
  
  • Pneumonitis from hydrocarbon aspiration
    
• ECG:
  
  • Dysrhythmias (atrial fibrillation, ventricular tachycardia, torsades de pointes, QT prolongation)
    
  • Bradycardia
    
  • Heart block
    
  • ST–T-wave abnormalities
    
• CT scan of head for altered mental status when diagnosis is uncertain
  

• Mild to moderate exposure:
  
  • Gastroenteritis
    
  • Asthma
    
  • Venomous arthropod bite (black widow, scorpion)
    
  • Progressive peripheral neuropathy (Guillain–Barré syndrome)
    
  • Carbon monoxide
    
• Severe exposure:
  
  • Narcotic overdose
    
  • Coma and miosis:
    
    • PCP, meprobamate, phenothiazine, clonidine
      
    • Muscarinic-containing mushrooms—cholinergic crisis without nicotinic symptoms
      
    • Nicotine poisoning
      
  • Metabolic and infectious:
    
    • Ketoacidosis, sepsis, meningitis, encephalitis
      
    • Hypoglycemia
      
    • Reye syndrome
      
  • Neurologic:
    
    • Cerebrovascular accident
      
    • Subdural or epidural hematoma
      
    • Postictal state
      

TREATMENT

• Decontamination is initial priority:
  
  • Decontaminate, airway, breathing, circulation (DABC)
    
  • Remove all clothes and store as toxic waste (double bagged)
    
• Protection of health care workers of utmost importance:
  
  • Impenetrable gloves (neoprene, nitrile), gowns, eye protection
    
• Decontaminate skin with soap and water:
  
  • Shower or gentle scrubbing ideal if done before entrance into the ED
    
• Maintain airway and oxygenate.
  
• IV access and place on cardiac monitor
  

• Decontaminate ABCs:
  
  • Decontamination and protection of staff
    
  • Maintain airway and oxygenate.
    
  • For unstable airway, intubate, and ventilate.
    
  • IV access with D
    ₅
    W 0.9% NS
    
• Altered mental status: Administer thiamine, glucose, and naloxone (Narcan)
  

• Atropine:
  
  • Blocks acetylcholine at muscarinic receptor sites.
    
  • No effect on nicotinic receptors
    
  • Onset of action is 1–4 min, peaks at 8 min.
    
  • Goal of therapy/end point:
    
    • Drying secretions of tracheobronchial tree
      
  • Administer test dose 1–2 mg IV/IM:
    
    • No clinical response: Double dose q5min until muscarinic findings subside
      
  • Dose: 1–4 mg IV q5min (peds: 0.05–0.2 mg/kg)
    
  • Common pitfalls in therapy:
    
    • Not giving enough atropine
      
    • Using pupillary findings (mydriasis) as end point of treatment
      
    • Mistaking dilated pupils or tachycardia as contraindications to atropine
      
• Pralidoxime (2-PAM):
  
  • Regenerates cholinesterase by reversing the phosphorylation of the enzyme.
    
  • Synergistic with atropine—muscarinic signs/symptoms will start to resolve in 10–40 min.
    
  • Side effects: Neuromuscular blockade with rapid infusion, respiratory arrest, HTN, nausea/vomiting, dizziness, blurred vision.
    
  • End point is resolution of muscle weakness and fasciculations.
    
  • Effective before enzyme aging occurs (permanent inactivation of cholinesterase)
    
  • Onset of aging varies among products
    
  • No restriction to its use even if 24–48 hr have passed
    
• Supportive care:
  
  • Dermal decontamination: Remove clothes and flush skin with water
    
  • Gastric lavage (early presentation of severe ingestion):
    
    • Gastric emptying with continuous suction via a nasogastric tube.
      
    • Handle contents with care—avoid direct contact to prevent personal exposure.
      
  • Respiratory difficulty:
    
    • Frequent oropharyngeal suction
      
    • Treat bronchospasm with atropine, not bronchodilators.
      
    • Tachycardia may result from hypoxia (pulmonary secretions and bronchospasm).
      
    • Atropine will dry secretions and paradoxically lower the heart rate.
      
    • Intubate and ventilate if necessary.
      
    • Avoid succinylcholine; may have prolonged duration as it is metabolized by cholinesterase.