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, hemolysis, coagulopathy, neuromuscular dysfunction
  • Up to 25% of bites are dry bites

Common Crotaline 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:
    • local tissue damage
    • Coagulapathies (pro and anti effects)
    • Platelet dysfunction
    • Neurotoxic effects

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

Differential Diagnosis

Envenomations, bites and stings

Diagnosis

Work-Up

  • CBC
  • Coags
  • Fibrinogen
  • FDP
  • Chemistry

Evaluation

  • 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

Treatment

Local Care

  • Do:
    • 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.

Crotalidae Polyvalent Immune Fab (FabAV) Antivenin (Crofab)

Indications

  • Progression of swelling
  • Abnormal results on lab tests (plt < 100,000 or fibrinogen < 100)
  • Systemic manifestations (unstable vitals or AMS)

Initial 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:the perform serial exams and consider maintenance therapy
    • If no: repeat infusion of 4-6 vials and then re-evaluate for control

Maintenance therapy

  • Maintance therapy may be indicated after initial dosing based on local protocols even if control is achieved.[1]
    • Infuse 2-vial doses at 6, 12, and 18hr after initial control achieved

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)

Antivenom 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 and is likely a result of isolated renal clearance of FabAV and persistent presence of actual venom in serum.[2]
    • Only described in patients with history of thrombocytopenia during hospital course
    • Warrants close monitoring of platelets by primary physician 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

Watch for 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

References

  1. Crofab treatment agorithmn http://www.crofab.com/documents/CroFab-Treatment_Algorithm.pdf
  2. Ruha AM et al. Late hematologic toxicity following treatment of rattlesnake envenomation with crotalidae polyvalent immune Fab antivenom. Toxicon. 2011;57:53–59.