American Pit Viper Snake Bites

Pit Vipers (sub-family Crotalinae) = rattlesnakes, cottonmouths (aka water moccasins), and copperheads

• See Pit Vipers of North Carolina for information on snake identification

Presentation :

• Classically presents w/ two puncture wounds, though a singular puncture wound does not exclude snake bite
• Some are "dry bites" (~25% of bites) with no venom injected and thus minimal symptoms
  
• Local toxicity: erythema, swelling, ecchymoses, pain (typically within 1h, up to 8+h). Tissue necrosis may develop.
  • Bites to the fingers or toes may result in autoamputation
  • Rattlesnake bites (particularly to upper extremities) can cause hemorrhagic bullae (40% of pts)
    
• Hematologic Toxicity: Prolonged PT/Inc INR, thrombocytopenia, and hypofibrinogenemia (akin to DIC). Nonetheless, frank bleeding/life-threatening bleeding is rare.
• Neurotoxicity: Uncommon; perioral/extremity paresthesias, bulbar abnormalities (eg, dysarthria, dysphagia), and myokymia (fasciculations of the face and proximal extremity muscles)
• Systemic:
  • Severe Envenomation: Nausea, vomiting, diarrhea, tachycardia, paresthesias, hypotension, and dizziness
  • Life-threatening Envenomation: Bleeding, hypotension, myokymia, weakness, and altered mental status

Pathophysiology :

• Venom contains a complex mixture of toxins, including phospholipase A2 (destroys membrane phospholipids), serine proteases (cleaves proteins), metalloproteinases (destroys extracellular matrix), thrombin-like enzymes (precipitating a DIC-like syndrome), etc

Diagnostic Testing:

• Signs/Symptoms may not develop immediately, monitor for 8-12h minimum up to 24h for high risk groups
• Draw a mark around the wound to monitor expansion, trend q15-30min
• CBC, PT/INR, fibrinogen to assess for hematologic toxicity; trend q6-8h
• BMP, CXR, EKG for systmic toxicity
• CK for compartment syndrome + neurotoxicity
• All patients who receive antivenom require follow-up monitoring (protocol based on product used) as late hemotoxicity may occur up to 14d later
• Monitor swollen extremities for compartment syndrome

Treatment :

• Consult with local poison control center
• First Aid:
  • Remove any rings, watches, or constrictive clothing from the affected extremity.
  • DO NOT apply pressure immobilization, tourniquets, or constrictive dressings as they worsen local tissue injury and there are no studies showing benefit in reducing systemic toxicity
  • Oral suction of venom IS NOT recommended as it does not remove significant venom but increases risk of infection w/ oral flora
• First manage ABCs.
  • Bites to face/neck are particularly high risk for progressing to airway obstruction and may merit intubation
  • Myokymia that is extensive, or involves the muscles of respiration, is associated with respiratory failure
  • Shock may develop requiring circulatory support
• Administer tetanus vaccine PRN
• Wound care: cleanse bite site with antiseptic (iodine or CHG), remove visible foreign bodies, elevate extremities to promote drainage of edema
• Prophylactic antibiotics for SSTI are not typically necessary, infection is rare unless wound is heavily contaminated
• Antivenom: should be given in consultation with poison control
  • Typically indicated for:
    • Bites to face/neck w/ swelling
    • Significant local swelling w/ progression
    • Hemotoxicity (elevated PT/INR, thrombocytopenia, hypofibrinogenemia)
      • Does not improve with coagulation factor replacement
    • Neurotoxicity
    • Systemic toxicity: hypotension, bleeding distant from site of bite, refractory vomiting/diarrhea
  • Administer in monitored setting (ER/ICU) to monitor for allergic reaction. Treat allergic rxn/Anaphylaxis as per usual
  • Two approved antivenom products in US:
    • CroFab: Ovine Crotalidae Polyvalent-immune Fab (FabAV)
      • Contraindications: allergy to papain, papaya, or FabAV
      • Requires maintenance doses to prevent recurrent toxicity (every 6 hours x3)
    • Anavip: Equine Crotalidae Immune F(ab')2 (Fab2AV)
      • Contraindications: allergy to horse protein, or FabAV
  • Redosing may be required if toxicity remains uncontrolled; may also be needed in cases of late hemotoxicity

Prognosis:

References:

• UpToDate