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Snake bites. Hussein Unwala Dr. Ingrid Vicas February 4, 2010. Objectives. Identifying Venomous Snakes Signs of Envenomation Treatment of Presumed Snakebites. Identifying the Pit Viper. Prairie rattlesnake - coiled and rattling Longest fangs 3-4 cm Significant local tissue destruction.

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Snake bites

Snake bites

Hussein Unwala

Dr. Ingrid Vicas

February 4, 2010


Objectives
Objectives

  • Identifying Venomous Snakes

  • Signs of Envenomation

  • Treatment of Presumed Snakebites



Prairie rattlesnake coiled and rattling longest fangs 3 4 cm significant local tissue destruction
Prairie rattlesnake - coiled and rattlingLongest fangs 3-4 cmSignificant local tissue destruction


Hey doc is this snake poisonous

“Red on Yellow Kills a Fellow”

Hey Doc! Is This Snake Poisonous?

Identifying Coral Snakes

Sonoran Coral Snake


Hey doc is this snake poisonous1
Hey Doc! Is This Snake Poisonous?

“Red on Black, Venom Lack”

Milk Snake - nonvenomous


Is the patient envenomated
Is the patient Envenomated?

  • Characteristics of a Venomous Snakebite

    • # strikes

    • Depth of envenomation

    • Size of snake

    • Potency/amount of venom injected

    • Size/health of victim

    • Location of bite


So how does this venom work
So how does this venom work?

  • “mosaic of antigens”

    • Proteolytic enzymes, procoagulants/anticoagulants, cardiotoxins, hemotoxins, neurotoxins

  • Venom is both circulating and tissue-fixed

    • Thus, anti-venom can halt progression, but won’t reverse clinical findings



  • What clinical signs are present1
    What Clinical Signs are Present?

    • Systemic Signs

      • Venom travels via lymph/superficial veins to enter circulation

        • Mild: weakness, malaise, nausea, restlessness

        • More Severe: confusion, abdominal pain/V/D, tachycardia, hypotension, blurred vision, salivation, metallic taste in mouth

        • Rare: DIC, MODS

        • In some envenomations, neurotoxins predominate

        • Anaphylaxis


    What lab findings might you expect
    What Lab Findings might you expect?

    • Platelets 10-50,000

    • Fibrinogen approaches Zero

    • PT, PTT immeasurably high

      • The majority of patients have no clinical bleeding!


    Okay now what
    Okay, now what?

    • Observing asymptomatic patients

      • 8-12 hours, if skin broken, and unable to ID snake

    • Pressure immobilization?

      • Do not occlude venous+arterial flow!

      • Broad, firm, constrictive wrap at 50-70mmHg

      • NOT recommended for NA pit viper envenomations

    • Venom Removal?

      • No benefit of negative pressure venom extraction


    Okay now what1
    Okay, now what?

    • Delineate extent of edema, measure diameter of extremity

    • Look for any signs of clinical bleeding

    • Labs initially, then q 4-6 h

    • Tetanus

    • Analgesia/Anxiolysis


    What about antivenom
    What About Antivenom?

    • First line therapy for moderate-severe envenomations

    • CroFab : ovine-derived Fab fragment

      • Fewer hypersensitivity reactions vs equine derived

      • Infused IV in 4-6 vials reconstituted in NS

        • Initiated at slow rate; if no signs of anaphylactoidrx, then rate is increased to complete the infusion over 1 hour

        • If progressive limb swelling, thrombocytopenia, coagulopathy, dose repeated prn

        • Once symptoms controlled, maintenance doses of 2 vials q 6h x 3 doses


    Surgery
    Surgery?

    • Initial routine use of tissue excision, fasciotomy, or “exploration and debridement” not recommended

    • Surgical debridement usually done 3-6 days post envenomation


    Other management points
    Other Management Points

    Low rates (0-3%) of wound infections

    No rationale for routine use of corticosteroids or anthistamines

    Careful followup of patients who received CroFab

    recurrence phenomenon

    serum sickness, delayed type hypersensitivity

    Fetal loss may be as high as 43% for bites during pregnancy

    Avoid any activity where risk of bleeding increased!!


    What about exotic snakes
    What about exotic snakes?

    • Efforts should be made to identify snake

    • Once snake identified, antivenom should be obtained

      • Local zoos, poison centers, snake collector

    • Give antivenom if signs of envenomation (ie fang marks!)

    • Compression immobillization of entire extremity



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