Rosen & Barkin's 5-Minute Emergency Medicine Consult (659 page)

• Description of snake
  
• Geographic location of bite
  

Search for manifestations of bites as described above.

• Careful exam of wound site and involved extremity:
  
  • Essential in judging severity of envenomation
    
  • Mark wound margins to follow progression
    
• Assess for anaphylactic reactions
  

• CBC
  
• Coags
  
• Fibrinogen,
  d
  -dimer
  
• Electrolytes, BUN/creatinine, glucose
  
• Creatine phosphokinase (CPK)
  
• UA
  
• Type and cross-match with moderate to severe envenomation.
  

Plain radiographs if foreign body suspected

• Nonvenomous snakes (in the US):
  
  • Narrow head
    
  • Round pupils
    
  • No rattles
    
• Pit vipers:
  
  • Triangular- or arrow-shaped head
    
  • Vertical or elliptical pupils
    
  • Heat-sensing pits just behind the nostrils and in front of eyes
    
  • ± Rattles
    
• Coral snakes (applies only in US, not internationally):
  
  • “Red on yellow—kill a fellow”
    
  • “Red on black—venom lack”
    

TREATMENT

• Retreat well beyond striking range of snake.
  
• Immobilize extremity in functional position at the level of heart.
  
• Keep physical activity minimal.
  
• Remove rings, watches, and all constrictive clothing.
  
• It is ill-advised to transport a snake to a health care facility for identification purposes:
  
  • If you are close enough to get a good picture with a camera/phone, you are too close to a potentially venomous snake.
    
  • Even severed head can envenomate.
    
• Controversies:
  
  • Pre-hospital local wound maneuvers are NOT recommended because they cause worse local tissue damage and increase the risk of infection. These include:
    
    • Incision and drainage
      
    • Mechanical suction devices
      
    • Oral suction
      
    • Tourniquets
      
    • Cryotherapy
      
    • Electrocution
      
    • Pressure immobilization
      
    • Incision attempts by inexperienced can lead to severe tendon, nerve, and vascular damage.
      

• Envenomation more likely to be severe.
  
• Severity due to relatively low body weight of small child with same volume of venom.
  

• Airway, breathing, and circulation management (ABCs)
  
• Maintain euvolemia with 0.9% normal saline (NS) to maintain renal blood flow
  
• Wound monitoring
  
• Immobilize bitten extremity
  

• Supportive care
  
• Monitor for compartment syndrome:
  
  • Repeated measurements of extremity circumference every 15–20 min until local progression/swelling subsides.
    
  • A true compartment syndrome is unlikely following rattlesnake envenomation.
    
  • Elevated compartment pressures are treated with more antivenom, as surgical intervention with fasciotomy causes more damage to the area.
    
  • Surgical therapy considered only in incredibly rare cases and should only be considered in consultation with a regional poison center and medical toxicologist
    
• Analgesia with IV opioids
  
• Tetanus prophylaxis if needed
  
• Broad-spectrum antibiotics not routinely indicated
  
• Steroids not indicated except for reactions to antivenom (see below)
  
• Routine use of blood products not indicated
  
• Wound severity:
  
  • Minimal:
    
    • Local swelling and tenderness
      
  • Moderate:
    
    • Extremity swelling
      
    • Evidence of systemic toxicity
      
  • Severe:
    
    • Obvious toxicity
      
    • Unstable vital signs
      
    • Coagulopathy
      
    • Elapid envenomation
      
    • Lab abnormalities
      

• Indications for Crotalid antivenom therapy:
  
  • More than minimal extremity swelling
    
  • Extremity swelling that is progressing
    
  • Clinical signs of systemic toxicity
    
  • Unstable vital signs
    
  • Coagulopathy (low platelets or fibrinogen, elevated PT)
    
• CroFab:
  
  • Fundamental treatment for North American pit viper envenomation
    
  • High-affinity purified ovine Fab antibody fragment antivenom
    
  • CroFab causes less frequent hypersensitivity reactions than older polyvalent antivenom
    
  • Pediatric antivenom dose = adult antivenom dose
    
  • Dosing: 4–6 vials initially
    
  • Reconstitute each CroFab vial with 25 mL sterile water. Dilute in 250 mL 0.9% NaCl and infuse over 1 hr.
    
  • If hypotensive or with serious active bleeding, initial dose is 8–12 vials
    
  • Evaluate for envenomation control 1 hr after antivenom bolus infusion. Control is defined by stable wound appearance, improving coagulation studies, and hemodynamic stability.
    
  • If envenomation control achieved after 1st bolus of antivenom, may need maintenance antivenom therapy at 2 vials q6h × 3 doses.
    
  • If envenomation control not achieved after 1st bolus of antivenom, repeat initial bolus and reassess. Discuss with regional poison center or medical toxicologist.
    
• Victims of envenomation who develop an allergic reaction to antivenom:
  
  • Stop infusion of antivenom
    
  • Administer antihistamines, corticosteroids, and fluids. Consider epinephrine for severe reactions.
    
  • Discussion of risks/benefits of restarting antivenom should take place with regional poison center or medical toxicologist
    
• Coral snake antivenom:
  
  • No longer being manufactured, but stockpile exists in geographically appropriate locales.
    
  • Effective against more toxic eastern coral snake but not against western coral snakes
    
  • After proper skin testing, 3–5 vials of antivenin recommended.
    
  • Treatment complications include anaphylaxis and serum sickness.
    
  • Coral snake venom is neurotoxic; watch for respiratory depression, control airway
    
• International exotic venomous snakes:
  
  • Specific antivenoms may be available at local zoos or through the Antivenom Index.
    

• Proportionally more antivenin per body weight
  
• Standard adult doses required
  

• If mother has systemic signs of envenomation toxicity, fetus is also at risk; timely antivenom therapy is still indicated.
  
• Consult obstetrician
  

• Contact local poison center 800-222-1222, medical toxicologist, local zoo, or regional herpetologist.
  
• Call Antivenom Index at 602-626-6016 in Tucson, Arizona, for assistance in treatment of exotic snakes not indigenous to US
  

FOLLOW-UP

• 24-hr observation after control of envenomation progression for patients requiring antivenom administration after pit viper bites.
  
• 24-hr observation for asymptomatic patients with elapid bites.
  
• ICU admission for:
  
  • Patients receiving antivenom
    
  • Evidence of moderate to severe envenomation, especially in children
    
  • All victims of elapid bites and for symptomatic exotic snake envenomations
    

Suspicious bite that shows no signs or symptoms of envenomation for 6–8 hr and has normal lab panel:

• Dry bites may be observed for 8 hr and discharged if there is no development in local toxicity and if lab studies normal.
  
• Minor envenomations should be observed for 12–24 hr and have labs repeated 6 hr after presentation, then again before discharge.
  
• Discharge with follow-up in 24 hr.
  

PCP or toxicology follow-up 1 wk after antivenom therapy to assess for possible serum sickness or envenomation wound infection.

• Avoid overly aggressive pre-hospital care interventions. It is best to rapidly transport to closest medical center.
  
• Be sure to administer proper dose of antivenom in a timely fashion when clinically indicated.
  

• American College of Medical Toxicology, American Academy of Clinical Toxicology, American Association of Poison Control Centers, et al. Pressure immobilization after North American Crotalinae snake envenomation.
  Clin Toxicol (Phila)
  . 2011;49:881–882.
  
• Corneille MG, Larson S, Stewart RM, et al. A large single-center experience with treatment of patients with crotalid envenomations: Outcomes with and evolution of antivenin therapy.
  Am J Surg
  . 2006;192:848–852.
  
• Cox MR, Reeves JK, Smith KM. Concepts in Crotaline snake envenomation management.
  Orthopedics
  . 2006;29(12):1083–1087.
  
• Cumpston KL. Is there a role for fasciotomy in Crotalinae envenomations in North America?
  Clin Toxicol (Phila).
  2011;49:351–365.
  
• Lavonas EJ, Ruha AM, Banner W, 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;11:2.
  

CODES

989.5 Toxic effect of venom