Crotaline envenomation

Background

• Includes rattlesnakes and copperheads
• Venom causes local tissue injury, hemolysis, coagulopathy, neuromuscular dysfunction
• Up to 25% of bites are dry bites

Clinical Features

1. Fang marks, localized pain, progressive edema extending from bite site
   1. Edema near the airway or in muscle compartment may threaten life or limb
2. Nausea/vomiting, oral numbness/tingling, dizziness, muscle fasciculations
3. Ecchymoses may appear within minutes to hours

Diagnosis

1. Must have a snakebite + evidence of tissue injury:
   1. Local injury (swelling, pain, ecchymosis)
   2. Hematologic abnormality (thrombocytopenia, elevated INR, hypofibrinogenemia)
   3. Systemic effects (oral swelling/paresthesias, metallic taste, hypotension, tachycardia)
2. Absence of all of the above 8-12hr after bite indicates dry bite

Work-Up

1. CBC
2. Coags
3. Fibrinogen
4. FDP
5. Chemistry

Treatment

1. Local Care
   1. Do not:
      1. Attempt to suck out the venom
      2. Place the affected part in cold water
      3. Use a tourniquet or wrap
   2. Do:
      1. Immobilize limb in a neutral position
2. Antivenom
   1. Crotalidae Polyvalent Immune Fab (FabAV)
   2. Indications:
      1. Progression of swelling
      2. Abnormal results on lab tests (plt < 100,000 or fibrinogen < 100)
      3. Systemic manifestations (unstable vitals or AMS)
   3. Administration
      1. The total volume but NOT the number of vials may be reduced in small children
      2. Establish initial control of envenomation by giving 4-6 vials
         1. Control achieved? (Cessation of progression of all components of envenomation, including labs checked 2 hours after infusion started)
            1. If yes infuse 2-vial doses at 6, 12, and 18hr after initial control achieved
            2. If no repeat infusion of 4-6 vials and then re-evaluate for control
   4. Envenomation control measurement
      1. Must observe for progression of envenomation during and after antivenom infusion
         1. Measure limb circumference at several site above and below bite
         2. Mark advancing border of edema q30min
         3. Repeat labs q4hr or after each course of antivenom (whichever is more frequent)
   5. Side Effects
      1. Acute reactions occur in <10% pts
      2. If occurs stop infusion and give antihistamines / epi if needed
   6. Recurrent thrombocytopenia has been described up to 2 weeks after transfusion with FabAV
      1. Likely 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
      3. warrants close monitoring of platelets by PMD or return visit after discharge
3. Supportive care
   1. IVF and pressors if needed for hypotension
   2. Blood component replacement indicated if antivenom fails to stop active bleeding
4. Compartment Syndrome
   1. If signs of compartment syndrome are present and pressure >30:
      1. Elevate limb
      2. Administer additional FabAV 4-6 vials IV over 60min
      3. If elevated compartment pressure persists another 60min consider fasciotomy

Disposition

1. Must observe all snakebite pts for at least 8hr before determining patient disposition
   1. Bites that initially appear innocuous and labs normal at presentation can be deceptive
2. Discharge if symptom-free after 8hr
3. Admit all pts receiving antivenom to the ICU
4. Admit pts to the ward if have completed or do not require further antivenom therapy

See Also

• Snake bites