Crotaline envenomation

Background

Rattlesnake

• 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

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

Differential Diagnosis

Necrotizing fasciitisCellulitisAllergic Reaction

Diagnosis

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:
  • 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 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]

Dosing and Administration

Initial Administration

• Initial dose: 6 vials
• 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
  • Maintance therapy may be indicated after initial dosing based on local protocols even if control is achieved.

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.
  • 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

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

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

• Snake bites
• Envenomation
• Crofab