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    Snake (Crotalus oreganus) Bites in British Columbia

    Critical Care / Resuscitation, Toxicology

    Last Updated Dec 27, 2022
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    First 5 Minutes

    Approach not well defined. Suggested approach based on BC DPIC monograph and Wilderness Medical Society Practice Guidelines.

    1. Rapid assessment of vital signs, airway, breathing, and circulation.
    2. Place patient on continuous cardiac, blood pressure, and pulse oximetry monitoring.
    3. Establish IV access in unaffected extremity.
    4. Treat anaphylaxis if present.
    5. Consider early intubation and ventilation especially for patient with facial or neck envenomation.
    6. Remove constrictive clothing and jewelry given risk of swelling.
    7. Mark leading edge of swelling and measure limb circumference. Repeat every 15 to 30 minutes until effects stabilized.
    8. Contact poison control for assistance and consideration of administering Antivenin (CroFab®).
    9. Reassure patient. Death is uncommon.


    Of the nine species of snakes in British Columbia, only the Western/Northern Pacific Rattlesnake (Crotalus oreganus) is truly venomous and poses a threat to humans.


    • The Western Rattlesnake can be identified by: (1) rattle on tail, (2) narrow, skinny neck, and (3) triangular head.
    • Medium size (0.6m to 1.2m when fully grown).
    • Colour is tan, olive, brown, or dark green with dark rectangular/ovoid patches running down dorsum.


    • The northern-most range of the Western Rattlesnake is Southern British Columbia (including Lillooet, Kamloops, Grand Forks, Osoyoos, Princeton, and the surrounding areas).

    Image 1: Crotalus Oreganus. From Wikimedia Commons. Accessed November 24, 2022. https://commons.wikimedia.org/w/index.php?search=Crotalus+oreganus&title=Special:MediaSearch&go=Go&type=image

    Diagnostic Process

    The diagnosis of envenomation is clinical and based on the following features that occur secondary to a bite from a Western Rattlesnake (Crotalus oreganus).

    Clinical Features:

    • Local → Enlarged lymph nodes, tissue edema, ecchymosis, and pain.
    • Systemic → Hypotension, diaphoresis, paresthesias, coagulation defects (decreased platelets, decreased fibrinogen, increased INR), anaphylaxis*.
    • HEENT → airway edema (even with extremity bites), metallic taste, oral paresthesias, ocular irritation/pain/erythema.
    • Cardiovascular → tachycardia (initial), bradycardia (later finding), hypotension.
    • Respiratory → dyspnea, non-cardiogenic pulmonary edema, adult respiratory distress syndrome*, respiratory failure related to fasciculations*.
    • Neurologic → weakness, fatigue, sweating, chills, pre-syncope, confusion*, fasciculations, paresthesias.
    • Gastrointestinal → N/V/D.
    • Genitourinary → hematuria, proteinuria, glycosuria.
    • Metabolic → metabolic acidosis.

    * uncommon.

    Recommended Investigations

    • Electrolytes.
    • CBC, creatinine.
    • INR, fibrinogen, platelets (repeat every 4 hours for minimum of 12 hours and then daily until normal).
    • CK.
    • Urinalysis.
    • Type and cross-match.

    Recommended Treatment

    Pre-Hospital Care

    1. Provide reassurance to patient. Death is UNCOMMON.
    2. Remove constricting items/jewelry.
    3. If an extremity was the location of the bite, immobilize with a splint and keep below the level of the heart.
    4. Immediately transport to health care facility.

    Do NOT:

    1. Apply ice.
    2. Apply tourniquet.
    3. Incise fang marks.
    4. Suck venom from wound using mouth or another suction device.

    Treatment approach should be focused on both local tissue injury/effects and systemic effects.

    Hospital Care


    1. Treat anaphylaxis with oxygen, epinephrine, and adjunctive medications.
    2. Consider early intubation and ventilation for patients who have suffered HEENT envenomation. Most patients will not require this.
    3. Swollen extremities are common. Acute compartment syndrome is uncommon but must be ruled out.  Pressures must remain >30-40mmHg for several hours with no response to elevation and immobilization, mannitol 1g/kg, and minimum of 4-6 vials of CroFab®.
    4. Monitor vital signs and systemic features (above) until resolution/normalization.
    5. Active bleeding unresponsive to antivenin may require administration of blood products
    6. Tetanus prophylaxis.
    7. Analgesia.
    8. Antibiotics are unnecessary.
    9. Corticosteroids may worsen local tissue injury. May be considered for delayed serum-sickness reactions.


    1. Monitor circumference of edema and erythema every 15-30 minutes until progression has stopped or slowed to <0.5cm per hour. Monitor for recurrence for minimum of 24 hours after last dose of antivenin.
    2. Cleanse bite area.
    3. If tourniquet present, remove slowly after initiation of antivenin.
    4. If ocular, flush eye with gentle, lukewarm water for 15 minutes. Consult ophthalmology.
    5. Surgical intervention is rarely required.

    Antivenin (Crotalidae Polyvalent Immune Fab (Ovine)) (CroFab®)

    • Mechanism → neutralizes venom, halts progression of local edema and necrosis, and improved coagulopathy.
    • Most effective within 6 hours of envenomation, but may be beneficial after this.
    • Indications → based on clinical features to assess degree of envenomation (e.g. worsening local injury, unstable vital signs, systemic signs of envenomation, coagulation abnormalities).
    • Not indicated for isolated fang marks without signs or symptoms of envenomation.
    • Initial Dose → initial dose 4 vials (6-12 indicated to achieve rapid control of severe coagulopathy, unstable vitals, or systemic toxicity).
    • Monitor → swelling should not progress across major joints, swelling should slow to <0.5cm/hour, coagulation studies should improve, systemic signs/vitals should improve.
    • Further Doses → If no improvements as above, administer another 4 vials and reassess after 1 hour. Repeat until control achieved.
    • Maintenance Dose → Administer 2 vials every 6 hours for 3 doses (total 6 vials). Monitor every hour for 6 hours.
    • Pediatric Dosing → same as adult.

    Criteria For Hospital Admission

    Patients with bites that do not suffer envenomation, with no symptoms, and normal bloodwork may be discharged after 8-12 hours of observation.

    Patients with non-progressive local symptoms and no systemic symptoms may be discharged after 12-24 hours of observation and serial bloodwork.

    Patients with progressive symptoms and/or systemic symptoms should be admitted for monitoring and administration of CroFab®.

    Criteria For Transfer To Another Facility

    Patients may require transport to a facility where they can receive in-patient care, and intensive care, if required.

    Bites involving the ocular or periorbital area require transport to a facility where ophthalmologic consultation available.

    Criteria For Safe Discharge Home

    Patients without symptoms and with normal blood work may be discharged after 8-12 hours of observation.

    Follow Up

    • Monitor INR, fibrinogen, and platelets every 2-3 days for 1-2 weeks after discharge.
    • Daily wound care of bite site.
    • Avoid ASA and NSAIDs for 2 weeks.
    • Restrict physical activity.
    • Avoid contact sports and dental work for 2-weeks given bleeding risk.
    • Physical therapy or occupation therapy may be beneficial in increasing mobilization of extremity.

    Quality Of Evidence?


    Disposition/Criteria for Admission

    Evidence is strong, but based on low-to-moderate studies. Primarily observational studies case control studies, or RCTs with limitations.


    Pre-Hospital Management

    Evidence is weak-strong, and based primarily on observational or case-control studies.


    Administration of Antivenin

    There is strong, high quality evidence of benefit clearly outweighing risks from RCTs without important limitations and observational studies with overwhelming evidence to support this recommendation.


    Recommendation to Contact Poison Control Centre

    There is strong, high quality evidence of benefit clearly outweighing risks from RCTs without important limitations and observational studies with overwhelming evidence to support this recommendation.


    Further Review

    Related Information

    Reference List

    1. BC Ministry of Environment and Climate Change Strategy and Thomson Rivers University.  Species Accounts: Snakes. BC Reptiles and Amphibians. Accessed November 24, 2022.  https://bcreptilesandamphibians.trubox.ca/species-reptiles/

    2. Poison Management Manual.  Rattlesnakes. BC Drug and Poison Information Centre; 2020. Accessed November 24, 2022. http://www.dpic.org/

    3. Poison Management Manual. Crotalidae Polyvalent Immune FAB (Ovine) – Antidote. BC Drug and Poison Information Centre; 2020. Accessed November 24, 2022. http://www.dpic.org/

    4. Kanaan NC, Ray J, Stewart M, Russell KW, Fuller M, Bush SP, Caravati M, Cardwell MD, Norris RL, Weinstein SA. Wilderness medical society practice guidelines for the treatment of pitviper envenomations in the United States and Canada. Wilderness and Environmental Medicine. 2015; 26: 472-487. doi:10.1016/j.wem.2015.05.007.


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