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Snake Envenomation, Emergency Medicine

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Snake Envenomation, Emergency Medicine

Basics

Description

Occur in zoos or in owners of exotic snakes

Search for manifestations of bites as described above.

Plain radiographs if foreign body suspected

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

  • Pit viper venom:Mixture of proteolytic enzymes and thrombin-like esterases:Enzymes cause local muscle and subcutaneous tissue necrosis.Esterases have defibrinating anticoagulant effect, leading to venom-induced consumption coagulopathy (VICC) in severe envenomations.
  • Bite location:Extremity bites most commonHead, neck, or trunk bites more severe than bite on extremities
  • Severe envenomation:Direct bite into artery or veinNeurotoxic envenomations
  • Bite mark significance:Pit viper bite: Classically includes 1 or 2 puncture marksNonvenomous snakes and elapids: Horseshoe-shaped row of multiple teeth marks
  • 25% of all pit viper bites are dry and do not result in envenomation.
  • Mixture of proteolytic enzymes and thrombin-like esterases:Enzymes cause local muscle and subcutaneous tissue necrosis.Esterases have defibrinating anticoagulant effect, leading to venom-induced consumption coagulopathy (VICC) in severe envenomations.
  • Enzymes cause local muscle and subcutaneous tissue necrosis.
  • Esterases have defibrinating anticoagulant effect, leading to venom-induced consumption coagulopathy (VICC) in severe envenomations.
  • Extremity bites most common
  • Head, neck, or trunk bites more severe than bite on extremities
  • Direct bite into artery or vein
  • Neurotoxic envenomations
  • Pit viper bite: Classically includes 1 or 2 puncture marks
  • Nonvenomous snakes and elapids: Horseshoe-shaped row of multiple teeth marks

Etiology

  • Pit vipers (Crotalinae):Account for 95% of all envenomationsRattlesnakes, cottonmouths, and copperheads
  • Coral snakes (Elapidae):NeurotoxicWestern coral snakes, found in Arizona and New MexicoMore venomous eastern coral snakes, found in Carolinas and Gulf states
  • Account for 95% of all envenomations
  • Rattlesnakes, cottonmouths, and copperheads
  • Neurotoxic
  • Western coral snakes, found in Arizona and New Mexico
  • More venomous eastern coral snakes, found in Carolinas and Gulf states
  • 30% of all snakebites involve patients younger than 20 yr. 12% of all snakebites are 9 yr or younger.
  • Because of their low body weight, smaller children and infants are more vulnerable to severe envenomation with systemic symptoms.

Diagnosis

Signs and Symptoms

  • Local (Crotaline):Classic skin changes:1 or 2 puncture woundsPain and swelling at siteSwelling and edema of involved extremity:Within 1 hr in severe envenomationsTender proximal lymph nodesEcchymosis, petechiae, and hemorrhagic vesicles develop within several hours.
  • Systemic (Crotaline):Weakness, dizzinessDiaphoresisNauseaScalp paresthesiasPeriorbital fasciculationsMetallic tasteSevere bites can lead to:Coagulopathy (VICC)HypotensionPulmonary edemaHematuriaRhabdomyolysisRenal failureCardiac dysfunctionPotential elevated compartment pressure in involved extremity
  • Symptoms (Crotaline):Primarily neurotoxic, leading to weakness, diplopia, confusion, delayed respiratory depression:Local effects may be deceivingly minimal.
  • Classic skin changes:1 or 2 puncture woundsPain and swelling at site
  • Swelling and edema of involved extremity:Within 1 hr in severe envenomationsTender proximal lymph nodes
  • Ecchymosis, petechiae, and hemorrhagic vesicles develop within several hours.
  • 1 or 2 puncture wounds
  • Pain and swelling at site
  • Within 1 hr in severe envenomations
  • Tender proximal lymph nodes
  • Weakness, dizziness
  • Diaphoresis
  • Nausea
  • Scalp paresthesias
  • Periorbital fasciculations
  • Metallic taste
  • Severe bites can lead to:Coagulopathy (VICC)HypotensionPulmonary edemaHematuriaRhabdomyolysisRenal failureCardiac dysfunction
  • Potential elevated compartment pressure in involved extremity
  • Coagulopathy (VICC)
  • Hypotension
  • Pulmonary edema
  • Hematuria
  • Rhabdomyolysis
  • Renal failure
  • Cardiac dysfunction
  • Primarily neurotoxic, leading to weakness, diplopia, confusion, delayed respiratory depression:Local effects may be deceivingly minimal.
  • Local effects may be deceivingly minimal.
  • Description of snake
  • Geographic location of bite

Essential Workup

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

Diagnosis Tests & Interpretation

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

Differential Diagnosis

  • Nonvenomous snakes (in the US):Narrow headRound pupilsNo rattles
  • Pit vipers:Triangular- or arrow-shaped headVertical or elliptical pupilsHeat-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 " 
  • Narrow head
  • Round pupils
  • No rattles
  • Triangular- or arrow-shaped head
  • Vertical or elliptical pupils
  • Heat-sensing pits just behind the nostrils and in front of eyes
  • ‚ ± Rattles
  • "Red on yellow " ”kill a fellow " 
  • "Red on black " ”venom lack " 

Treatment

Pre-Hospital

  • 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 drainageMechanical suction devicesOral suctionTourniquetsCryotherapyElectrocutionPressure immobilizationIncision attempts by inexperienced can lead to severe tendon, nerve, and vascular damage.
  • 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.
  • 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 drainageMechanical suction devicesOral suctionTourniquetsCryotherapyElectrocutionPressure immobilizationIncision attempts by inexperienced can lead to severe tendon, nerve, and vascular damage.
  • 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.

Initial Stabilization/Therapy

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

Ed Treatment/Procedures

  • 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 tendernessModerate:Extremity swellingEvidence of systemic toxicitySevere:Obvious toxicityUnstable vital signsCoagulopathyElapid envenomationLab abnormalities
  • 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
  • Minimal:Local swelling and tenderness
  • Moderate:Extremity swellingEvidence of systemic toxicity
  • Severe:Obvious toxicityUnstable vital signsCoagulopathyElapid envenomationLab abnormalities
  • Local swelling and tenderness
  • Extremity swelling
  • Evidence of systemic toxicity
  • Obvious toxicity
  • Unstable vital signs
  • Coagulopathy
  • Elapid envenomation
  • Lab abnormalities
  • Indications for Crotalid antivenom therapy:More than minimal extremity swellingExtremity swelling that is progressingClinical signs of systemic toxicityUnstable vital signsCoagulopathy (low platelets or fibrinogen, elevated PT)
  • CroFab:Fundamental treatment for North American pit viper envenomationHigh-affinity purified ovine Fab antibody fragment antivenomCroFab causes less frequent hypersensitivity reactions than older polyvalent antivenomPediatric antivenom dose = adult antivenom doseDosing: 4 " “6 vials initiallyReconstitute 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 vialsEvaluate 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 ƒ — 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 antivenomAdminister 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 snakesAfter 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.
  • 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)
  • 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 ƒ — 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.
  • 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
  • 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
  • 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

Disposition

  • 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 antivenomEvidence of moderate to severe envenomation, especially in childrenAll victims of elapid bites and for symptomatic exotic snake envenomations
  • Patients receiving antivenom
  • Evidence of moderate to severe envenomation, especially in children
  • All victims of elapid bites and for symptomatic exotic snake envenomations
  • 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.

Followup Recommendations

Pearls and Pitfalls

  • 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.

Additional Reading

  • 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

ICD9

ICD10

  • T63.001A Toxic effect of unsp snake venom, accidental, init
  • T63.011A Toxic effect of rattlesnake venom, accidental, init
  • T63.021A Toxic effect of coral snake venom, accidental, init
  • T63.061A Toxic effect of venom of N & S American snake, acc, init
  • T63.091A Toxic effect of venom of snake, accidental, init

SNOMED

  • 238457002 Venomous snake bite (finding)
  • 217659000 poisoning due to rattlesnake venom (disorder)
  • 217653004 poisoning due to coral snake venom (disorder)
  • 217652009 poisoning due to copperhead snake venom (disorder)
  • 217661009 poisoning due to viper venom (disorder)
  • 217662002 Poisoning due to water moccasin venom (disorder)
  • 241811004 poisoning due to bite of unidentified snake (disorder)