Basics
Description
- 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 common
- Head, neck, or trunk bites more severe than bite on extremities
- Severe envenomation:
- Direct bite into artery or vein
- Neurotoxic envenomations
- Bite mark significance:
- Pit viper bite: Classically includes 1 or 2 puncture marks
- Nonvenomous snakes and elapids: Horseshoe-shaped row of multiple teeth marks
- 25% of all pit viper bites are dry and do not result in envenomation.
Etiology
Venomous Snakes Indigenous to US
- Pit vipers (Crotalinae):
- Account for 95% of all envenomations
- Rattlesnakes, cottonmouths, and copperheads
- Coral snakes (Elapidae):
- Neurotoxic
- Western coral snakes, found in Arizona and New Mexico
- More venomous eastern coral snakes, found in Carolinas and Gulf states
International Exotic Venomous Snakes
Occur in zoos or in owners of exotic snakes
- 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 wounds
- Pain and swelling at site
- Swelling and edema of involved extremity:
- Within 1 hr in severe envenomations
- Tender proximal lymph nodes
- Ecchymosis, petechiae, and hemorrhagic vesicles develop within several hours.
- Systemic (Crotaline):
- Weakness, dizziness
- Diaphoresis
- Nausea
- Scalp paresthesias
- Periorbital fasciculations
- Metallic taste
- Severe bites can lead to:
- Coagulopathy (VICC)
- Hypotension
- Pulmonary edema
- Hematuria
- Rhabdomyolysis
- Renal failure
- Cardiac dysfunction
- Potential elevated compartment pressure in involved extremity
- Symptoms (Crotaline):
- Primarily neurotoxic, leading to weakness, diplopia, confusion, delayed respiratory depression:
- Local effects may be deceivingly minimal.
History
- Description of snake
- Geographic location of bite
Physical Exam
Search for manifestations of bites as described above.
Essential Workup
- Careful exam of wound site and involved extremity:
- Essential in judging severity of envenomation
- Mark wound margins to follow progression
- Assess for anaphylactic reactions
Diagnosis Tests & Interpretation
Lab
- CBC
- Coags
- Fibrinogen, d-dimer
- Electrolytes, BUN/creatinine, glucose
- Creatine phosphokinase (CPK)
- UA
- Type and cross-match with moderate to severe envenomation.
Imaging
Plain radiographs if foreign body suspected
Differential Diagnosis
- 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
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 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 tenderness
- Moderate:
- Extremity swelling
- Evidence of systemic toxicity
- Severe:
- Obvious toxicity
- Unstable vital signs
- Coagulopathy
- Elapid envenomation
- Lab abnormalities
Antivenom
- 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
Treatment Assistance
- 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
Admission Criteria
- 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
Discharge Criteria
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.
Followup Recommendations
PCP or toxicology follow-up 1 wk after antivenom therapy to assess for possible serum sickness or envenomation wound infection.
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
989.5 Toxic effect of venom
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)