Envenomation

Michael Daw

General Principles

  • Survey for severe systemic reactions (e.g. anaphylaxis) 
  • Perform routine wound care (soap/water), elevation, manage acute pain 
  • Administer antivenom if indicated and monitor for adverse reactions (e.g. anaphylaxis, serum sickness) 
  • Administer tetanus prophylaxis as indicated 
  • Antibiotics if signs of concurrent cellulitis 
  • At VUMC, consult toxicology 
  • Consider calling the Poison Control center 1-800-222-1222

Snake Bites

  • In North America, envenomation is usually caused by Crotalids (e.g. pit vipers, rattlesnakes, water moccasins, copperheads), less commonly by Elapids (coral snakes) 
  • 25% of venomous snakebites are dry and no venom is released 
  • Clinical features: 
    • Localized pain, edema, bruising and blister formation (6-36 hours) and later necrosis 
    • Coagulopathy (DIC), neurotoxicity (muscle weakness, CN palsy, dysphagia, paresthesia, respiratory compromise), distributive shock - more common from Elapids (up to 12 hours after bite) 
  • Evaluation: CBC, CMP, Coags, fibrinogen, CK, UA 
  • Management: 
    • Asymptomatic or mild symptoms can be monitored without antivenom and serial labs for 6-12 hours 
    • Moderate to severe reactions (widely distributed reaction, systemic signs, or hemodynamic compromise) should receive antivenom and be admitted for at least 24 hours observation

Spider Bites

  • Brown recluse (Loxoscelism): 
    • Often found in homes (attics, basements, cupboards) and outdoors, numbers increase with human population size (synanthropic) 
    • Local signs: painless bite, painful blister within hours (red plaque/papule with central pallor, sometimes with vesiculation), 10-20% progress to eschar/necrosis that will ulcerate and heal over weeks to months 
    • Systemic signs (no correlation with bite appearance): nausea/vomiting, fever, malaise, rhabdomyolysis, acute hemolytic anemia, DIC and renal failure. Myocarditis (rare) 
    • Evaluation: 
      • Local symptoms only: no further workup 
      • Systemic: CBC, CMP, Coag studies, CK, UA, hemolysis labs if anemic (smear, retic count, HFP, LDH, haptoglobin) 
    • Management: 
      • Admit if expanding wounds/systemic symptoms + consult toxicology! 
      • Skin necrosis: symptomatic/supportive care. Surgical intervention can worsen cosmetic outcomes and is rarely indicated. 
      • Hemolytic anemia: generally, transfuse for Hgb > 9-10. Rapidity of hemolysis is more important than the absolute Hgb. 
      • Rhabdomyolysis: LR for UOP >200-300cc/hr 
      • If patient develops chest pain: EKG/troponin; if either is abnormal obtain echo and call Toxicology given concern for myocarditis. 
      • DIC: supportive care. 
  • Black Widow (Latrodectism): 
    • Local signs: painful bite, circular red macule that progresses to target-like lesion 
    • Systemic signs: muscle pain and rigidity that starts at the bite site, autonomic neurologic symptoms (tachycardia, nausea, diaphoresis) 
    • Evaluation: 
      • Local symptoms only: no further workup 
      • Cardiac: EKG, troponins 
    • Management: 
      • Admit if moderate to severe symptoms 
      • Benzodiazepines +/ opiates are effective for muscle pain and spasms 
      • Considerr antivenom if severe symptoms, young children, older adults, or pregnant individuals

Hymenoptera Stings

  • Bees, wasps, hornets, fire ants account for 10% of all anaphylaxis in the US. Treat anaphylaxis promptly with epinephrine. 
  • Local reactions: remove retained stingers, apply cold compress, oral antihistamines, NSAIDs, topical corticosteroids. 
  • Consider steroid taper for large local reactions. 
  • Swarm attacks can lead to severe systemic reactions with end organ damage, including rhabdomyolysis and AKI (typically >50 stings), rarely myocardial infarction.
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