Crotaline (Pit Vipers)

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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, coagulopathy,and thrombocytopenia
  • 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
  • Nausea/vomiting, oral numbness/tingling, dizziness, muscle fasciculations
  • Ecchymoses may appear within minutes to hours

Differential Diagnosis

Evaluation

Work-Up

  • CBC
  • Coags
  • Fibrinogen
  • Chemistry

Evaluation

    • Local injury (Pain, Progressive Swelling, 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)
    • Systemic effects (hypotension resulting from third spacing)

Management

Local Care

  • Do:
    • Immobilize limb in a neutral position
    • Remove all jewelry
  • Do not:
    • Attempt to suck out the venom
    • Place the affected part in cold water
    • Use a tourniquet or wrap

Crofab administration

  • See below

Supportive care

  • IVF and pressors if needed for hypotension
  • Blood components 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)

Dosing and Administration

  • Administer antivenom as soon as possible if the indications are met and antivenom is available.[1]
  • Administration should slow swelling and decrease pain

Initial Administration

CroFab is reconstituted in normal saline and typically diluted into 250 cc or 1 L of normal saline and infused over an hour.

  • The dosing of CroFab is the same for adults and children (may have to adjust the dilution of CroFab for small children so that they are not volume overloaded)
  • 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: then 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 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.[3]
    • 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. Dart RC et al. Efficacy of post envenomation administration of antivenin. Toxicon. 1988;26:1218–1221.
  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.