II. Epidemiology

  1. U.S. Incidence
    1. Total: 45,000 Snake Bites in U.S. per year
    2. Venomous bites: 8000 to 9000 in U.S. per year (almost all are Pit Viper bites)
    3. Deaths from Snake Bite in U.S.: 12 or less per year
    4. Envonomation occurs in 75% of U.S. poisonous SnakeBites
  2. Worldwide Snake Bites (esp. Africa, Asia, Latin America)
    1. Incidence: 1.8 to 2.7 Million Snake Bites/year worldwide (50% are venomous)
    2. Roughly 81,000 to 138,000 deaths per year worldwide from Snake Bites
    3. Roughly 300,000 amputations per year worldwide from Snake Bites

III. Causes: U.S. Poisonous snakes

  1. Pit Vipers or Crotalidae (99% U.S. venomous bites)
    1. Characteristics
      1. Broad, triangle-shaped head with elliptical pupils and heat sensing loreal pits
      2. Fangs are long and retractable
    2. Rattlesnake (Crotalus or Sisturus genera)
      1. Most common poisonous snake in U.S.
      2. Potent venom
      3. Responsible for 95% of deaths (esp. Diamondback)
    3. Cottonmouth, water moccasin (Agkistrodon piscivorous)
      1. Aggressive water snakes in Southeastern U.S.
      2. Moderately potent venom
    4. Copperhead (Agkistrodan contortix)
      1. Least potent venom
  2. Coral Snakes (Family Elapidae)
    1. Characteristics
      1. Round heads with round pupils, and smooth scales
      2. Fangs are short and fixed
        1. Transfer venom via chewing instead of injection
    2. Nonaggressive poisonous Coral Snakes of the southern U.S.
      1. Arizona Sonoran Coral Snake (Micruroides Euryxanthus)
      2. Texas Coral Snake (Micrurus Tener)
        1. Neurotoxic effects may present with findings similar to Botulism
      3. Eastern Coral Snake (Micrurus Fulvius)
        1. Primarily in the southeast United States (Mississippi and Alabama south to Florida)
    3. Worldwide, Elapidae are among the most dangerous, infamous poisonous snakes
      1. Cobras
      2. Kraits
      3. Sea snakes
      4. Mambas

IV. History

  1. Snake appearance (photo if available) and suspected variety or species
  2. Time elapsed since Snake Bite
  3. Symptoms and their timing since the Snake Bite occurred
  4. Last tetanus Vaccination

V. Signs and Symptoms: Pit Vipers (except Mojave rattler)

  1. Snake characteristics
    1. Long movable fangs cause skin puncture marks
    2. Broad triangular heads with elliptical eyes and heat sensing pits between the eyes and nostrils
    3. Bites may be deceptively small or appear as scratches and still result in severe Envenomations
    4. Up to 25% of pit viper bites deliver no venom (dry bites)
      1. All bites should be presumed venomous initially (delays increase morbidity and mortality)
  2. Local Tissue Necrosis
    1. Mechanism: Venom alters Coagulation Factors (via Thrombin-like Glycoproteins) resulting in consumptive Coagulopathy
    2. Immediate pain and burning at bite site
    3. Within a few minutes to 30 minutes, redness and swelling develops (may extend to include entire extremity)
    4. Bite site develops a purplish discoloration, hemorrhagic bullae and necrosis within hours
  3. Generalized signs and symptoms (Hemotoxic effects)
    1. Nausea and Vomiting
    2. Dizziness and Hypotension
    3. Weakness
    4. Sweats and chills
    5. Metallic or Rubbery taste in mouth
  4. Generalized neurotoxic effects (only with U.S. West Coast Rattlesnakes: Mojave, tiger and some timber Rattlesnakes)
    1. Muscle Fasciculations
  5. Systemic complications
    1. Disseminated Intravascular Coagulation (DIC)
    2. Acute Renal Failure
    3. Hypovolemic Shock (7% of cases)
    4. Rhabdomyolysis (if muscle Fasciculations)
    5. Compartment Syndrome (rare)
  6. Course
    1. Not immediately fatal unless Envenomation into vein

VI. Signs and Symptoms: Coral Snakes (Elapidae)

  1. Characteristics
    1. Small fixed fangs cause tiny semicircular scratches
    2. Bites are painful
    3. Venom contains a Neurotoxin (primarily affecting Acetylcholine receptors)
      1. Results in paralysis
      2. Contrast with the pit viper related local tissue injury and cogualopathy
    4. Coral Snake: Red stripe next to yellow stripe ("Red next to yellow, you're a dead fellow")
      1. Contrast with King Snake
        1. Red stripe next to black stripe ("Red next to black, venom they lack")
      2. This rule applies only in the U.S.
        1. Outside the U.S., Red and Black snakes may be venomous
  2. Generalized symptoms may be delayed 1-8 hours (local effects may have onset in first 15 min)
    1. Drowsiness, Weakness
    2. Paresthesias with numbness at bite site
    3. Bulbar Paralysis with Ptosis, Ophthalmoplegia or Dysphagia
    4. Blurred Vision
    5. Slurred speech
    6. Salivation
    7. Seizures
  3. Systemic complications (develop over time after initial visual effects)
    1. Descending Flaccid Paralysis
    2. Cardiac Arrest or respiratory arrest may occur

VII. Labs

  1. Blood Type and Cross Match
  2. Urinalysis
  3. Chemistry panel (e.g. Chem8)
    1. Renal Function tests (BUN and Creatinine)
    2. Serum Electrolytes
    3. Serum Glucose
  4. Complete Blood Count with Platelet Count
    1. Thrombocytopenia occurs with pit viper bites
      1. May be delayed (repeat Platelet Count in 7-10 days)
  5. Liver Function Tests
  6. Creatine Kinase (CK)
    1. May be increased in Pit Viper Bites (esp. with Timber Rattlesnake)
  7. Coagulation Factors (draw baseline and at 12 hours)
    1. Prothrombin Time (PT/INR)
      1. May be increased in Pit Viper Bites
    2. Partial Thromboplastin Time (PTT)
    3. Fibrinogen
      1. May be decreased in Pit Viper Bites
    4. Fibrin Split Products
    5. D-Dimer
      1. May be increased in Pit Viper Bites
    6. Creatine Phosphokinase (CPK)
  8. Other studies that may be indicated (esp. Coral Snake bites)
    1. Arterial Blood Gas (ABG)
    2. Waveform Capnography
    3. Pulmonary Function Tests
    4. Troponin I

VIII. Differential Diagnosis

  1. Anaphylaxis
    1. Presents with Hypotension, Tachycardia and Angioedema (similar to severe Envenomation)

IX. Diagnostics

X. Management: First Aid in Field

  1. Get to a medical facility equipped with antivenom as soon as possible (ideally by EMS)
    1. Decompensation may occur rapidly
  2. Calm and reassure patient
  3. Attempt to identify snake type from a distance (photo, color and pattern description)
    1. Do not try to capture the snake for Identification
    2. Do not attempt to handle even a dead snake (Envenomations occur from intact bite reflex)
    3. Adult snake versus baby snake is unlikely to change management (both can cause severe Envenomations)
  4. Do not leave a patient alone
  5. Have the patient lie down
  6. Immobilize bite area
    1. Rattlesnake: Level with the heart
    2. Non-Rattlesnake Pit Viper: Above the level of the heart (may reduce local tissue swelling and inflammation)
    3. Coral Snake: Below the level of the heart (may reduce systemic toxin distribution)
  7. Remove jewelry or clothing that tighten with swelling
  8. Clean the bite area with soap and water
    1. Irrigate the wound with clean water or saline
    2. Apply antiseptic solution and gauze if available
  9. Mechanical venom suction devices are NOT recommended (only remove 2% of venom)
    1. Previously small vacuum venom extractor devices were recommended
      1. Had previously been indicated within 5 minutes of bite, left in place for 30 min
    2. Do not cut wound or try to suck out venom
    3. Avoid harmful methods (see below) at bite site
  10. Low pressure constriction band (NOT a Tourniquet!)
    1. Indicated if medical assistance is >1 hour away and neurotoxic effects are expected
      1. Primarily indicated for Coral Snake bites (not pit vipers)
      2. Australians apply Crepe Wrapping (ACE Wrap from distal to proximal extremity) to impede lymph flow
        1. Theoretically prevents Neurotoxin proximal spread and paralysis
        2. NOT indicated in United States (where we do not have the same neurotoxic snakes)
    2. Wrap A band (ACE, belt, sock) 2-3 inches above bite
      1. Band should be wide and flat
      2. Band applied between bite site and heart
    3. Do not cut off arterial circulation (again, NOT a Tourniquet)
      1. Pressure: 20 mmHg
      2. Be able to slip a finger between band and skin
    4. Leave band in place until medical facility
    5. Contraindications to low pressure constriction band
      1. Gila Monster
      2. Copperhead
      3. Water moccasin
      4. Pygmy Rattlesnake

XI. Management: Emergency Department

  1. Contact poison control immediately (in U.S., 1-800-222-1222)
    1. Local zoo herpetologist may also be helpful in snake identification
  2. ABC Management
    1. Angioedema may occur requiring airway management
    2. Do not draw blood or start IV in affected extremity
    3. Start Intravenous Fluids
    4. Manage Hypotension (IV fluids, Vasopressors)
    5. Consider Epinephrine and Corticosteroids if signs of Anaphylaxis
  3. Bite Wound Management
    1. Clean and irrigate the wound
    2. Tetanus Toxoid
    3. Opioid Analgesics are often needed (esp. pit viper bites)
    4. Elevate extremity >60 degrees (reduces pain by decreasing localized swelling)
    5. Even wounds that appear deceptively small or scratch-like may result in severe Envenomation
    6. Prophylactic antibiotics are not recommended (<5% infection risk)
  4. Antivenom
    1. See Snake Antivenin
    2. Administer antivenom as soon as possible
      1. However there is not a fixed time window at which point it is too late to give to a symptomatic patient
    3. Indications (even for seemingly mild pit viper bites)
      1. Any signs of systemic Envenomation (e.g. Nausea, Vomiting)
      2. Hypotension or cardiovascular toxicity
      3. Neurotoxicity or myotoxicity (coral Snake Envenomation)
      4. Lab abnormalities (e.g. Thrombocytopenia, low Fibrinogen, increased INR)
      5. Progressive and significant erythema, swelling or pain
      6. Spontaneous systemic bleeding or Coagulopathy
      7. Bites involving the hand or foot (esp. fingers or toes)
    4. Monitor labs at baseline (see above), one hour after antivenom, and then every 6 hours until stable
    5. Monitor for Anaphylaxis and anaphylactoid reactions
    6. Recheck at 48 to 72 hours for repeat CBC, Fibrinogen (for hematologic toxicity)
  5. Suspected pit viper bite management (local swelling and inflammation)
    1. Observe asymptomatic patients 8-12 hours after bite
      1. One quarter of bites are "dry" without venom injected
    2. Monitor frequent pulse checks (every 30 minutes) at a point distal to the bite site
      1. Pulse check with Capillary Refill
      2. Circumferential measurement around extremity bite wounds
    3. Mark leading edge of bite site swelling and erythema every 30 minutes
    4. Hospital admission for any patient who received antivenom
      1. May discharge if stable swelling and labs for 24 hours
    5. Indications for discharge
      1. No proximal spread of extremity findings
      2. Normal laboratory studies
      3. Patient able to return immediately for worsening
      4. Patient should return for Coagulopathy signs or pain not relieved with limb elevation
  6. Suspected Coral Snake bite management
    1. Observe asymptomatic patient for at least 12-24 hours
    2. Monitor neurologic status and respiratory status closely
    3. Requires immediate treatment and antivenin
    4. Neurologic complications may be delayed
    5. Consider Anticholinergics (Atropine, neostigmine)
    6. Hospital admission for any patient who received antivenom
    7. Intubation and Ventilator support may be required
      1. Indicated for Forced Vital Capacity <50% of predicted

XII. Precautions: Avoid harmful methods

  1. Do not cut skin at bite site
  2. Fasciotomy is rarely indicated
    1. Compartment Syndrome may be controlled by antivenin
    2. Only Consider if hourly serial ICP >30 mmHg
  3. Do not use electric shock or stun gun at bite site
  4. Do not apply tightly constricting Tourniquet
  5. Do not administer antivenin in the field
    1. Risk of Anaphylaxis
  6. Delayed Thrombocytopenia (antivenin-refractory) may occur
    1. Recheck Platelet Count again in 7-10 days

XIII. Prevention

  1. On coming upon a snake:
    1. Slowly and quietly move away, and allow it to escape
    2. Do not expect a warning before they strike
      1. Most snakes do not hiss or rattle before striking
    3. Do not handle any snake (even if snake appears dead)
  2. Be alert in areas commonly inhabited by snakes
    1. Hiking, picnicking, camping and firewood areas
    2. Water areas
    3. Tall grass, underbrush, abandoned buildings
    4. Piles of logs, rocks, and branches
  3. Be careful of areas of decreased visibility
    1. Avoid reaching into holes and crevices
    2. Avoid jumping over logs and fences
    3. Pull logs or rocks toward you when turning over
    4. Avoid placing fingers under objects being lifted
  4. Prepare for a hike
    1. Wear boots and long pants
    2. Carry a flashlight for nighttime conditions
    3. Hike with a companion
  5. Reduce residential risks of Snake Bite
    1. Provide lighting for yard, sidewalks, and patio
    2. Keep yard mowed and bushes pruned
    3. Keep home free of mice

XIV. References

  1. Cowling and Ferreri (2019) Crit Dec Emerg Med 33(2): 17-25
  2. Cowling and Lowes (2024) Crit Dec Emerg Med 38(1): 4-13
  3. Mason and Brandehoff (2020) EM:Rap 20(9): 13-4
  4. (1998) Postgrad Med 103(4): 311 [PubMed]
  5. Juckett (2002) Am Fam Physician 65(7):1367-74 [PubMed]
  6. Lavonas (2011) BMC Emerg Med 11:2 +PMID: 21291549 [PubMed]
  7. McKinney (2001) Ann Emerg Med 37(2):168-74 [PubMed]

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