Hussein Unwala Dr. Ingrid Vicas February 4, 2010

 Identifying Venomous Snakes  Signs of Envenomation  Treatment of Presumed Snakebites

Identifying the Pit Viper

Identifying Coral Snakes “Red on Yellow Kills a Fellow” Sonoran Coral Snake

Milk Snake - nonvenomous “Red on Black, Venom Lack”

 Characteristics of a Venomous Snakebite ◦ # strikes ◦ Depth of envenomation ◦ Size of snake ◦ Potency/amount of venom injected ◦ Size/health of victim ◦ Location of bite

 “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

 Local Reactions Extent of Envenomation Clinical ObservationsAntivenom Recommendation a Other TreatmentDisposition None ("dry bite")Fang marks may be seen, but no local or systemic symptoms after 8-12 hours NoneLocal wound care Tetanus prophylaxis Discharge after 8-12 hours of observation MinimalMinor local swelling and discomfort only, with no systemic symptoms or hematologic abnormalities NoneLocal wound care Tetanus prophylaxis Admit to monitored unit for 24-hour observation ModerateProgression of swelling beyond area of bite, with local tissue destruction, hematologic abnormalities, or systemic symptoms YesIV fluids Cardiac monitoring Analgesics Follow laboratory values Tetanus prophylaxis Admit to ICU SevereMarked progressive swelling and pain, with blisters, bruising, and necrosis; systemic symptoms such as vomiting, fasciculations, weakness, tachycardia, hypotension, and severe coagulopathy YesIV fluids Cardiac monitoring Analgesics Follow laboratory values Oxygen Vasopressors PRN Tetanus prophylaxis Admit to ICU

 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

 Platelets 10-50,000  Fibrinogen approaches Zero  PT, PTT immeasurably high ◦ The majority of patients have no clinical bleeding!

 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

 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

 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 anaphylactoid rx, 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

 Initial routine use of tissue excision, fasciotomy, or “exploration and debridement” not recommended  Surgical debridement usually done 3-6 days post envenomation

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!!

 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