Crotaline envenomation

Background
  • The Crotalinae subfamily of Viperidae classifies the new world vipers, or pit vipers. The snakes have a pitlike depression behind the nostril that contains a heat-sensing organ used to find prey.
  • Includes rattlesnakes and copperheads
  • Venom causes local tissue injury, coagulopathy,and thrombocytopenia
  • Up to 25% of bites are dry bites

Common Crotaline (Pit Viper) snake names
  • Rattlesnake
  • Cottonmouth
  • Copperhead
  • Sidewinder
  • Water moccasin
  • Massasauga

Venom
  • Venom form a Crotaline mainly damages local tissue via metalloproteinases and hyaluronidase which cause swelling edema and damage to capillaries.
  • Clinical effects consist of:
Rattlesnake

Clinical Features
  • Fang marks, localized pain, progressive edema extending from bite site
  • Nausea/vomiting
  • Oral numbness/tingling
  • Dizziness
  • Muscle fasciculations
  • Ecchymoses may appear within minutes to hours

Differential Diagnosis

Envenomations, bites and stings

Evaluation

Work-Up
  • CBC
  • Coags
  • Fibrinogen
  • Chemistry

Evaluation
  • Local injury (pain, progressive swelling, compartment syndrome, lymphangitic spread with pain in the axillae for upper extremity bites or pain in the inguinal region for lower extremity)
  • Hematologic abnormality (thrombocytopenia, prolonged PT, hypofibrinogenemia) - DIC-like syndrome
  • Systemic effects (hypotension resulting from third spacing)

Management

Local Care
  • Do:
    • Immobilize limb in a neutral position
    • Remove all jewelry
    • Mark the leading edge of erythema/edema
  • Do not:
    • Attempt to suck out the venom
    • Place the affected part in cold water
    • Use a tourniquet or wrap
    • Antivenom is first line treatment for compartment syndrome; fasciotomy is last resort if elevated pressures persist.

Crofab administration
  • See below

Supportive care
  • IVF and vasopressors if needed for hypotension
  • Blood products rarely needed

Crotalidae Polyvalent Immune Fab (FabAV) Antivenin (Crofab)

Indications

The following are criteria for administration after Crotalidae bite [3]

  • Progression of swelling
  • Abnormal results on lab tests (platelet < 100,000 or fibrinogen < 100)
  • Systemic manifestations (unstable vitals or altered mental status)

Initial Administration
  • Initial dose: 6 vials[1]
  • Typically diluted into 250 cc or 1 L of normal saline and infused over an hour
  • Same dose for both adults and pediatrics (may have to adjust the dilution of CroFab for small children so that they are not volume overloaded)

Maintenance therapy
  • May repeat dose (2 vials) at 6, 12, and 18 hours later if symptoms not controlled[2]
    • Maintance therapy may be indicated after initial dosing based on local protocols even if control is achieved.[3]

Envenomation control measurement
  • Observe for progression of envenomation during and after antivenom infusion
  • Measure limb circumference at several sites 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 allergic reactions occur in <10% pts
    • If occurs stop infusion and give epinephrine/antihistamines if needed
  • Recurrent thrombocytopenia has been described up to 2 weeks after transfusion with FabAV and is likely a result of isolated renal clearance of FabAV and persistent presence of actual venom in serum.[4]
    • Warrants close monitoring of platelets by primary physician or return visit after discharge
  • Serum sickness is unlikely but precautions should be given to patents upon discharge

Disposition
  • Observe all snakebite patients for at least 6hr before determining patient disposition
    • Bites that initially appear innocuous and labs normal at presentation can be deceptive
  • Discharge if symptom-free after 6hr
  • Admit all patients receiving antivenom to the ICU

See Also

References
  1. Gerardo CJ. The efficacy of crotalidea polyvalent immune fab (ovine) antivenom versus placebo plus optional rescue therapy on recovery from copperhead snake envenomation: A randomized, double-blind, placebo-controlled, clinical trial. Annals of EM. August 2017. 70(2):233-244.
  2. Gerardo CJ. The efficacy of crotalidea polyvalent immune fab (ovine) antivenom versus placebo plus optional rescue therapy on recovery from copperhead snake envenomation: A randomized, double-blind, placebo-controlled, clinical trial. Annals of EM. August 2017. 70(2):233-244.
  3. Crofab treatment agorithmn http://www.crofab.com/documents/CroFab-Treatment_Algorithm.pdf
  4. Ruha AM et al. Late hematologic toxicity following treatment of rattlesnake envenomation with crotalidae polyvalent immune Fab antivenom. Toxicon. 2011;57:53–59.
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