Crotaline envenomation

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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.

Crofab administration

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


Crotalidae Polyvalent Immune Fab (FabAV) Antivenin (Crofab)

Indications

The following criteria for administration after Crotalidae bite allows for clinician judgment and shared decision making with the patient due to the extreme cost of Crofab[1]

  1. Progression of swelling
  2. Abnormal results on lab tests (plt < 100,000 or fibrinogen < 100)
  3. Systemic manifestations (unstable vitals or AMS)
  4. Neuromuscular toxicity

No studies show reduction in mortality from antivenom administration.

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.[2]
    • 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.[3]
    • Only described in patients with history of thrombocytopenia during hospital course
    • Warrants close monitoring of platelets by primary physician or return visit after discharge

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. Lavonas EJ et al: Unified treatment algorithm for the management of crotaline snakebite in the United States: results of an evidence-informed consensus workshop. BMC Emerg Med. 2011; 11.
  2. Crofab treatment agorithmn http://www.crofab.com/documents/CroFab-Treatment_Algorithm.pdf
  3. Ruha AM et al. Late hematologic toxicity following treatment of rattlesnake envenomation with crotalidae polyvalent immune Fab antivenom. Toxicon. 2011;57:53–59.