Crotaline envenomation: Difference between revisions
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==Crotalidae Polyvalent Immune Fab (FabAV) Antivenin ([[Crofab]])== | ==Crotalidae Polyvalent Immune Fab (FabAV) Antivenin ([[Crofab]])== | ||
Revision as of 22:30, 20 July 2016
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
- 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
- FDP
- 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 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]
- Progression of swelling
- Abnormal results on lab tests (plt < 100,000 or fibrinogen < 100)
- Systemic manifestations (unstable vitals or AMS)
- Neuromuscular toxicity
No studies show reduction in mortality from antivenom administration.
Initial Administration
- Initial dose: 6 vials[2]
- 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[3]
- Maintance therapy may be indicated after initial dosing based on local protocols even if control is achieved.[4]
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.[5]
- 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
- Must observe all snakebite patients 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 patients receiving antivenom to the ICU
- Admit patients to the ward if have completed or do not require further antivenom therapy
See Also
References
- ↑ 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.
- ↑ Gerardo CJ. The efficacy of crotalidea polyvalent immune fab (ovine) antivenom versus placebo plus optional rescue therapy on recovery from copperhead snake envenomation: A randomized, double-blind, placebo-controlled, clinical trial. Annals of EM. August 2017. 70(2):233-244.
- ↑ Gerardo CJ. The efficacy of crotalidea polyvalent immune fab (ovine) antivenom versus placebo plus optional rescue therapy on recovery from copperhead snake envenomation: A randomized, double-blind, placebo-controlled, clinical trial. Annals of EM. August 2017. 70(2):233-244.
- ↑ Crofab treatment agorithmn http://www.crofab.com/documents/CroFab-Treatment_Algorithm.pdf
- ↑ Ruha AM et al. Late hematologic toxicity following treatment of rattlesnake envenomation with crotalidae polyvalent immune Fab antivenom. Toxicon. 2011;57:53–59.