Emergency Medicine Resident
28 yo F presents to ED s/p snake bite at 2200. States that she was trying to catch a rattlesnake in Nelson, NV. She states that it is a sidewinder (this knowledge due to the fact that she is an avid snake hobbyist). While attempting to catch the snake the pt was bit by 1 fang at her L 3rd DIP joint of her UE. She did not present for 4 hours as she thought that this bite was unsubstantial. When the swelling increased she called to multiple hospitals and presented to the only hospital with antivenom. Other than swelling pt had no other substantial symptoms. Vital signs are Temp: 98.0 HR: 80 RR: 16 BP: 140/85 SpO2 98% RA. Pt’s labs are remarkable for WBC of 15.2, platelets of 90, Potassium of 3.3, PT of 14.4, and INR of 1.3. The first treatment should be:
A. Fresh Frozen Plasma
B. Weight based antivenom
C. KCL IV 80 mg STAT
D. 4-6 vials of antivenom regardless of weight
E. Intubation
A. 4-6 vials of antivenom regardless of weight
Clinical Pearls
- Snake envenomation should be considered in any individual who presents with reported bite or suspected bite with a constitution of neurological symptoms and/or coagulopathy.
- Snake envenomations that warrant antivenom include the Western Diamondback Rattlesnake, Eastern Diamondback Rattlesnake, Mojave Rattlesnake, and Water Moccasin (Cottonmouth).
- Crofab dosage is severity based as opposed to weight based and reverses neurotoxicity and most venom induced coagulopathies.
Pathophysiology
- Locally Acting Toxins
- Consist of enzymes that cause tissue destruction.
-phospholipase A2 -peptidases,
-phosphodiesterases -metalloproteinases
-hyaluronidases
- Consist of enzymes that cause tissue destruction.
- Neurotoxins
- Presynaptic- based on PLA2 and damage terminal axon. Non-reversible (days-weeks recovery)
- Postsynaptic- long/short chain peptides that antagonizes Acetylcholine receptors on the muscle endplate. Sometimes reversed with antivenom and/or anticholinesterases.
- Myotoxins
- Local Muscle Necrosis
- Rhabdomyolysis
- Local Muscle Necrosis
- Systemic Myotoxins
- Systemic Hemostasis Toxins
- Anticoagulation- primarily through targeting Factors V, IX, and X. Others target include Fibrinogenolysis and inhibition of VWF. Reversed by antivenom
- Pro thrombotic less common, but may result in DVT, PE, and/or CVA. Targets include Factor II activation and/or activation of VWF.
- Blood Vessel Damage
- Cardiotoxins
- ACE-Inhibition and Naturetic Peptide induced hypotension
- Kidney
- Direct action of some venoms
- AKI from rhabdomyolysis/hypotension
- Misc. Toxins
Symptoms/Exam Findings
- Local/systemic pain
- Local/systemic paresthesias
- Tachycardia
- Hypotension
- Compartment Syndrome
- Ptosis
- Mydriasis
- Poor Facial Tone
- Limited Mouth opening/tongue extrusion
- Drooling
- Decreased DTRs
- Gait Disturbances
- Cranial Nerve Dysfunction
- Edema
- Skin necrosis/ecchymosis
- DIC
- Respiratory Depression
- Nausea and vomiting
- Erythema
- Urticaria
- Sweating
Indications (US):
- C Atrox (Western Diamondback Rattlesnake),
- C Adamanteus (Eastern Diamondback Rattlesnake),
- C Scutulatus (Mojave Rattlesnake),
- A Piscivous (Cottonmouth/Water Moccasin)
Pros:
- Since development snakebite mortality has dropped from 36% in the 1950s to 0.06% in 2009.
- Neutralizes neurotoxins
- Halts progression of coagulopathy in most pts
Cons:
- Hypersensitivity (Immediate in 6% and Delayed in 8%)
- Shorter half life than actual venom
- Expensive (around $20,000 per vial)
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