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Snake Bite Wounds

- See: necrotizing fascitis

- Discussion:
    - snake bite resources
    - snake types:
         - pit vipers (crotaline) which include rattlesnakes, cottonmouths, and copperheads;
               - crotalus (rattlesnakes)
               - agkistrodon (copperheads, water moccasins)
               - micrurus (coral snakes)

- Epidemiology:
            - 15% of the approximately 3000 species of snakes worldwide are considered harmful to humans
            - 1998-2001 – AAPCC reports annual average 6,000 snakebites, 2,000 of which were from venomous snakes
            - true incidence - 7000-8000 bites by venomous snakes resulting in 5-6 deaths per year
            - eastern and western diamondback rattlesnakes account for most fatalities
            - deaths typically in children, elderly, and those either not receiving antivenom, receiving antivenom after significant delay or inadequate quantities
            - victims typically are male between 17-27 years old
            - 98% of bites are on the extremities
            - most bites occur between April and September
            - alcohol intoxication is a major factor (70%)

- Envenomation:
    - Implies that enough venom introduced to cause local or systemic signs
    - 25% of all pit viper bites are “dry”, 50% of all coral snake bites
    - Snake parts should not be handled directly, or handled with care– the bite reflex in recently killed/decapitated snakes remains intact
    - dx requires positive identification of the snake and clinical manifestations of envenomation            
    - 20% of snake bites in US are non-poisonous

- Pharmacology of Snake Bites:
    - Chemically complex mixture of proteins, peptides and enzymes
    - Designed to immobilize, kill, and digest prey
    - Highly stable – resistant to temp changes, drying, drugs
    - Bind to multiple receptor sites
    - Lethal components – smaller LMW polypeptides
    - Quantity, lethality and composition varies with species, age, geography, time of year
    - Damage to endothelial cells of vascular walls, causing blebs in the endothelium, dilating the perinuclear space, and breaking down the plasma membrane
    - Affect almost every organ system – esp. CV, heme, respiratory, nervous

- Dart Severity Scoring:
    - grade 0: no envenomation.  fang marks and minimal pain.
    - grade I:
          - minimal envenomation. fang marks, pain, 1 to 5 inches of edema and erythema in 1st 5 hours;
          - no systemic symptoms;
    - grade II:
          - moderate envenomation. fang marks, pain, 6-12 inches of edema in first 12 hours;
          - systemic symptoms may be present along with rapid progression of signs from grade I.
          - may have bleeding from bite site;
    - grade III:
          - severe envenomation. fang marks, pain, edema greater than 12 inches in first 12 hours.
          - systemic symptoms, including coagulation defects;
          - signs of grade I and II envenomation appear in rapid progression;
    - grade IV:
          - very severe envenomation.  local reaction develops rapidly.
          - edema may involve ipsilateral trunk. ecchymoses, necroses, and blebs develop.
          - potential for compartment syndrome;

- Treatment Considerations:
    - US national hotline: national hotline at 800-222-1222
    - work up:
         - serial measurements of vital signs especially BP for minimum of 8 hours (note delayed response to venom);
         - laboratory data: a minority of patients will require pRBC transfusion, FFP, or even platlets;
         - H and H
         - platlet count
         - bleeding disorders / PT/PTT (need to rule out consumptive coagulopathy);
         - creatine kinase
         - urinalysis
         - compartment syndrome
         - infection
         - antivenom:
                - antivenoms are directed against two main groups: crotaline (pit vipors) and coral snakes
                - antivenom (CroFab; FabAV) composed of purified Fab specific to indigenous snake species
                - Fab molecules have a shorter half-life than IgG molecules and may allow recurrence of venom effects, if additional doses are not administered (systemic effects may reoccur hours or even days after treatment);
                - Fab preparation has produced fewer acute or delayed (serum sickness) allergic reactions;
         - indications for treatment:
                - most indicated for systemic symptoms, but in some cases, it may be used for rapidly advancing local symptoms;
                        - worsening local injury (eg, swelling, ecchymosis);
                        - clinically important coagulation abnormality, or systemic effects (eg, hypotension, altered mental status);
                - be aware that over use of antivenom will lead to cases of anaphylaxis;
                - antivenom is composed of purified Fab specific to indigenous snake species
                - Fab preparation has produced fewer acute or delayed (serum sickness) allergic reactions;
         - dosage: adequate dosage will reverse systemic effects (usually 8-12 vials);
         - complications:
                - anaphylaxis
                - overall rate of serum sickness after the administration of FabAV is about 15 percent

Bacteriology of rattlesnake venom and implications for therapy.

Bacteriology of human and animal bite wounds.

The efficacy of tourniquets as a first-aid measure for Russell's viper bites in Burma.

Tourniquet application after cobra bite: delay in the onset of neurotoxicity and the dangers of sudden release.

Crotalid envenomation: the southern Arizona experience.

Rattlesnake Bites in Children: Antivenin Treatment and Surgical Indications

Initial Experience with Crotalidae Polyvalent Immune Fab (Ovine) Antivenom in the Treatment of Copperhead Snakebite

Pediatric snakebites: lessons learned from 114 cases

Bites of Venomous Snakes