Crotaline envenomation

Background

  • Includes rattlesnakes and copperheads
  • Venom causes local tissue injury, hemolysis, coagulopathy, neuromuscular dysfunction
  • Up to 25% of bites are dry bites
Rattlesnake

Clinical Features

  • Fang marks, localized pain, progressive edema extending from bite site
    • Edema near the airway or in muscle compartment may threaten life or limb
  • Nausea/vomiting, oral numbness/tingling, dizziness, muscle fasciculations
  • Ecchymoses may appear within minutes to hours

Diagnosis

  • Must have a snakebite + evidence of tissue injury:
    • Local injury (swelling, pain, ecchymosis)
    • Hematologic abnormality (thrombocytopenia, elevated INR, hypofibrinogenemia)
    • Systemic effects (oral swelling/paresthesias, metallic taste, hypotension, tachycardia)
  • Absence of all of the above 8-12hr after bite indicates dry bite

Work-Up

  • CBC
  • Coags
  • Fibrinogen
  • FDP
  • Chemistry

Differential Diagnosis

Envenomations, bites and stings

Treatment

  • Local Care
    • Do not:
      • Attempt to suck out the venom
      • Place the affected part in cold water
      • Use a tourniquet or wrap
    • Do:
      • Immobilize limb in a neutral position
  • Antivenom
    • Crotalidae Polyvalent Immune Fab (FabAV)
    • Indications:
      • Progression of swelling
      • Abnormal results on lab tests (plt < 100,000 or fibrinogen < 100)
      • Systemic manifestations (unstable vitals or AMS)
    • Administration
      • The total volume but NOT the number of vials may be reduced in small children
      • Establish initial control of envenomation by giving 4-6 vials
        • Control achieved? (Cessation of progression of all components of envenomation, including labs checked 2 hours after infusion started)
          • If yes infuse 2-vial doses at 6, 12, and 18hr after initial control achieved
          • If no repeat infusion of 4-6 vials and then re-evaluate for control
    • Envenomation control measurement
      • Must observe for progression of envenomation during and after antivenom infusion
        • Measure limb circumference at several site above and below bite
        • Mark advancing border of edema q30min
        • Repeat labs q4hr or after each course of antivenom (whichever is more frequent)
    • Side Effects
      • Acute reactions occur in <10% pts
      • If occurs stop infusion and give antihistamines / epi if needed
    • Recurrent thrombocytopenia has been described up to 2 weeks after transfusion with FabAV
      • Likely result of isolated renal clearance of FabAV and persistent presence of actual venom in serum
      • Only described in patients with history of thrombocytopenia during hospital course
      • warrants close monitoring of platelets by PMD or return visit after discharge
  • Supportive care
    • IVF and pressors if needed for hypotension
    • Blood component replacement indicated if antivenom fails to stop active bleeding
  • Compartment syndrome
    • If signs of compartment syndrome are present and pressure >30:
      • Elevate limb
      • Administer additional FabAV 4-6 vials IV over 60min
      • If elevated compartment pressure persists another 60min consider fasciotomy

Disposition

  • Must observe all snakebite pts for at least 8hr before determining patient disposition
    • Bites that initially appear innocuous and labs normal at presentation can be deceptive
  • Discharge if symptom-free after 8hr
  • Admit all pts receiving antivenom to the ICU
  • Admit pts to the ward if have completed or do not require further antivenom therapy

See Also

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