Suspected Snake bites?
Injury resulting from snake biting a human.
Physical Finding and Clinical Presentation
In addition to local tissue injury, envenomation may affect the renal, neurologic, gastrointestinal, vascular, and coagulation systems. Symptoms vary widely depending on type of envenomation. Not all snakebites are poisonous, and not all bites lead to envenomation. Species-specific signs and symptoms following envenomation are discussed.
CROTALIDAE (PIT VIPERS)
In addition to local tissue injury, envenomation may affect the renal, neurologic, gastrointestinal, vascular, and coagulation systems. Symptoms vary widely depending on type of envenomation. Not all snakebites are poisonous, and not all bites lead to envenomation. Species-specific signs and symptoms following envenomation are discussed.
CROTALIDAE (PIT VIPERS)
Local Signs and Symptoms
Pain within 5 min
Edema within 30 min
Erythema of site and adjacent tissues/serous or hemorrhagic bullae, ecchymosis, and/or lymphangitis over the ensuing hours
If no edema or erythema is manifested within 8 hr after a confirmed crotalid snakebite, it is safe to assume envenomation did not occur. (Roughly 25% of cases do not involve envenomation.) In general, rattlesnake bites are more severe than those of the other snakes in the Crotalidae family.
Edema within 30 min
Erythema of site and adjacent tissues/serous or hemorrhagic bullae, ecchymosis, and/or lymphangitis over the ensuing hours
If no edema or erythema is manifested within 8 hr after a confirmed crotalid snakebite, it is safe to assume envenomation did not occur. (Roughly 25% of cases do not involve envenomation.) In general, rattlesnake bites are more severe than those of the other snakes in the Crotalidae family.
Systemic manifestations may include:
Mild to moderate nausea/vomiting, perioral paresthesias, metallic taste, tingling of fingers or toes (especially with rattlesnake bites), and/or fasciculations (local or generalized)
Severe hypotension (due to increased vascular permeability), mental status change, respiratory distress, tachycardia, acute renal failure, rhabdomyolysis, and coagulopathies including intravascular hemolysis and disseminated intravascular coagulation.
ELAPIDAE (CORAL SNAKES):
Severe hypotension (due to increased vascular permeability), mental status change, respiratory distress, tachycardia, acute renal failure, rhabdomyolysis, and coagulopathies including intravascular hemolysis and disseminated intravascular coagulation.
ELAPIDAE (CORAL SNAKES):
Local symptoms are far less pronounced (little or no pain/swelling immediately after the bite).
Neurologic symptoms are more common due to neurotoxins in elapid venom.
Systemic symptoms predominate, but onset may be delayed for up to 12 hr. Examples include:
1. Altered mental status and cranial nerve palsies featuring ptosis, dysphagia, or dysarthria
2. Tremors
3. Intense salivation, nausea, vomiting, or abdominal pain
4. Loss of DTRs and respiratory depression (late manifestations)
Differential Diagnosis
Harmless snakebite
Scorpion bite
“Dry bite”
Insect bite
Cellulitis
Laceration or puncture wound
Necrotizing fasciitis
Neurologic symptoms are more common due to neurotoxins in elapid venom.
Systemic symptoms predominate, but onset may be delayed for up to 12 hr. Examples include:
1. Altered mental status and cranial nerve palsies featuring ptosis, dysphagia, or dysarthria
2. Tremors
3. Intense salivation, nausea, vomiting, or abdominal pain
4. Loss of DTRs and respiratory depression (late manifestations)
Differential Diagnosis
Harmless snakebite
Scorpion bite
“Dry bite”
Insect bite
Cellulitis
Laceration or puncture wound
Necrotizing fasciitis
Workup
An estimated 25% of venomous snakebites do not result in envenomation, but all cases of suspected envenomation should be observed for 8 hr or longer
Check for signs of envenomation.
1. Swelling, tenderness, redness, ecchymosis, or blebs at the bite site
2. Elevated protime, decreased fibrinogen or platelets
3. Systemic signs such as hypotension, bleeding complications, vomiting, diarrhea, angioedema, or neurotoxicity
Determine if patient has indications for antivenom. Continual reassessment is indicated throughout the observation period because severity of symptoms may change.
Laboratory Tests
For all suspected envenomations, obtain CBC (with peripheral smear and platelet count), DIC screen (PT/INR, PTT, fibrinogen, fibrin degradation products, d-dimer), ECG, serum electrolytes, BUN, Cr, and urinalysis. Serial measurements of hemoglobin, platelets, protime, and fibrinogen are needed to monitor for acute and delayed hematologic complications.
For more severe bites, consider LFTs, sedimentation rate, creatine kinase (rule out rhabdomyolysis), ABG, and type and crossmatch.
Other: consider chest radiograph in cases with severe envenomation or in patients over 40 years old with underlying cardiopulmonary disease; radiograph of bite site for retained fangs (poor sensitivity); head CT if concern is raised for intracranial hemorrhage
Treatment
IN THE FIELD: For a suspected snakebite:
An estimated 25% of venomous snakebites do not result in envenomation, but all cases of suspected envenomation should be observed for 8 hr or longer
Check for signs of envenomation.
1. Swelling, tenderness, redness, ecchymosis, or blebs at the bite site
2. Elevated protime, decreased fibrinogen or platelets
3. Systemic signs such as hypotension, bleeding complications, vomiting, diarrhea, angioedema, or neurotoxicity
Determine if patient has indications for antivenom. Continual reassessment is indicated throughout the observation period because severity of symptoms may change.
Laboratory Tests
For all suspected envenomations, obtain CBC (with peripheral smear and platelet count), DIC screen (PT/INR, PTT, fibrinogen, fibrin degradation products, d-dimer), ECG, serum electrolytes, BUN, Cr, and urinalysis. Serial measurements of hemoglobin, platelets, protime, and fibrinogen are needed to monitor for acute and delayed hematologic complications.
For more severe bites, consider LFTs, sedimentation rate, creatine kinase (rule out rhabdomyolysis), ABG, and type and crossmatch.
Other: consider chest radiograph in cases with severe envenomation or in patients over 40 years old with underlying cardiopulmonary disease; radiograph of bite site for retained fangs (poor sensitivity); head CT if concern is raised for intracranial hemorrhage
Treatment
IN THE FIELD: For a suspected snakebite:
Transport immediately to nearest medical facility. No treatments in the field should delay travel to the nearest facility where an antivenom agent can be given if necessary.
Immobilize affected part.
Remove any constricting items. Applying tourniquets, incising, and applying suction to the wound is discouraged. Tourniquets cause more local tissue damage due to tissue necrosing venom seen in crotalid bites and should not delay transport to a medical facility.
Do not apply ice; keep victim warm.
Avoid alcohol, stimulants (caffeine), or agents that can suppress mental status.
IN THE HOSPITAL
Immobilize affected part.
Remove any constricting items. Applying tourniquets, incising, and applying suction to the wound is discouraged. Tourniquets cause more local tissue damage due to tissue necrosing venom seen in crotalid bites and should not delay transport to a medical facility.
Do not apply ice; keep victim warm.
Avoid alcohol, stimulants (caffeine), or agents that can suppress mental status.
IN THE HOSPITAL
Record vital signs: BP, HR, T, RR, and O2 sat.
Establish intravenous access and initiate IV hydration with crystalloid if the patient is hypotensive.
Obtain time of bite and description of snake if possible. Crotalids have a triangle-shaped head, nostril holes (pits), and elliptical pupils. The most dangerous of the crotalids is the rattlesnake, distinguished by its telltale rattle. Elapids, like the western and eastern coral snakes of the U.S., have brightly colored red, black, and yellow stripes.
Obtain and initiate reconstitution of appropriate antivenom. (Antivenoms are typically supplied in powder form and must be reconstituted before administration. If using older antivenoms, this process can take up to 1 hr, so it is recommended that it be initiated as soon as the patient arrives in the ED.)
1. Inspect site of bite for fang marks and local symptoms.
2. Delineate margins of erythema/edema with a marker.
3. Measure circumference of bitten part at two or more proximal sites and compare with unaffected limb; repeat every 15 to 20 min; assess for extension of erythema/edema.
4. Conduct a complete neurologic examination.
5. Obtain past medical history; ask about allergies to horse serum in those previously treated for snakebite.
If no signs of envenomation:
1. Clean and immobilize affected part.
2. Immunize against tetanus.
3. For crotalid bites, observe patient for at least 8 hr. If, at the end of this interval, local and systemic sequelae are absent and lab values remain normal, the likelihood of significant envenomation is low, and the patient can be discharged from the acute setting. Some sources recommend observing patients with crotalid bites to the lower extremities for at least 24 hours because swelling in the larger compartments of the legs could be slower and less easily recognizable. All definitive elapid bites should be treated. If elapid bite is only suspected, the patient must be monitored for up to 18 hr as symptoms can be delayed.
Patients who have progressive local symptoms or any systemic symptoms should be considered for antivenom. Crotalid envenomations without any progressive local or any systemic symptoms can be monitored for 12 to 24 hours, with repeat labs obtained 4 to 6 hours before discharge. If they have no new symptoms during that period of observation, they may be safely discharged. Specifically, copperhead bites often need no further interventions.
TREATMENT OF NONNATIVE (EXOTIC) SNAKEBITES
Establish intravenous access and initiate IV hydration with crystalloid if the patient is hypotensive.
Obtain time of bite and description of snake if possible. Crotalids have a triangle-shaped head, nostril holes (pits), and elliptical pupils. The most dangerous of the crotalids is the rattlesnake, distinguished by its telltale rattle. Elapids, like the western and eastern coral snakes of the U.S., have brightly colored red, black, and yellow stripes.
Obtain and initiate reconstitution of appropriate antivenom. (Antivenoms are typically supplied in powder form and must be reconstituted before administration. If using older antivenoms, this process can take up to 1 hr, so it is recommended that it be initiated as soon as the patient arrives in the ED.)
1. Inspect site of bite for fang marks and local symptoms.
2. Delineate margins of erythema/edema with a marker.
3. Measure circumference of bitten part at two or more proximal sites and compare with unaffected limb; repeat every 15 to 20 min; assess for extension of erythema/edema.
4. Conduct a complete neurologic examination.
5. Obtain past medical history; ask about allergies to horse serum in those previously treated for snakebite.
If no signs of envenomation:
1. Clean and immobilize affected part.
2. Immunize against tetanus.
3. For crotalid bites, observe patient for at least 8 hr. If, at the end of this interval, local and systemic sequelae are absent and lab values remain normal, the likelihood of significant envenomation is low, and the patient can be discharged from the acute setting. Some sources recommend observing patients with crotalid bites to the lower extremities for at least 24 hours because swelling in the larger compartments of the legs could be slower and less easily recognizable. All definitive elapid bites should be treated. If elapid bite is only suspected, the patient must be monitored for up to 18 hr as symptoms can be delayed.
Patients who have progressive local symptoms or any systemic symptoms should be considered for antivenom. Crotalid envenomations without any progressive local or any systemic symptoms can be monitored for 12 to 24 hours, with repeat labs obtained 4 to 6 hours before discharge. If they have no new symptoms during that period of observation, they may be safely discharged. Specifically, copperhead bites often need no further interventions.
TREATMENT OF NONNATIVE (EXOTIC) SNAKEBITES
For bites by exotic or nonnative snakes, contact a Poison Control Center or your local zoo. (Zoos with exotic snakes are required to maintain a supply of snake-specific antivenom on their premises.)
Complications
Allergic reactions were very frequent with horse serum antivenoms. CroFab from sheep serum should be preferentially used over equine serum if available.
Anaphylaxis occurs within 30 min and should be treated by immediately stopping the infusion to managing the symptoms of anaphylaxis, including epinephrine SQ or IM initially and IV if needed, diphenhydramine IV, and hydrocortisone IV. If the anaphylactic symptoms can be managed and the envenomation is severe, the infusion can then be resumed.
Delayed hematologic complications are common and can manifest up to 4 days post treatment. Most bleeding is self-limited but can rarely be severe, necessitating close follow-up.
Serum sickness occurs 7 to 14 days after antivenom administration and is characterized by fever, rash, arthralgias, and lymphadenopathy. It can be treated with prednisone 60 mg/d PO, tapered over 7 to 10 days.
Injuries also result from:
1. Tourniquet placement on the field, which should be avoided
2. Ice application (cryotherapy), which can worsen tissue damage
Complications
Allergic reactions were very frequent with horse serum antivenoms. CroFab from sheep serum should be preferentially used over equine serum if available.
Anaphylaxis occurs within 30 min and should be treated by immediately stopping the infusion to managing the symptoms of anaphylaxis, including epinephrine SQ or IM initially and IV if needed, diphenhydramine IV, and hydrocortisone IV. If the anaphylactic symptoms can be managed and the envenomation is severe, the infusion can then be resumed.
Delayed hematologic complications are common and can manifest up to 4 days post treatment. Most bleeding is self-limited but can rarely be severe, necessitating close follow-up.
Serum sickness occurs 7 to 14 days after antivenom administration and is characterized by fever, rash, arthralgias, and lymphadenopathy. It can be treated with prednisone 60 mg/d PO, tapered over 7 to 10 days.
Injuries also result from:
1. Tourniquet placement on the field, which should be avoided
2. Ice application (cryotherapy), which can worsen tissue damage
