Approximately 7,500–10,000 venomous snakebites occur annually in the US, with >95% caused by crotaline pit vipers (rattlesnakes, copperheads, cottonmouths) and a small minority by coral snakes (Elapidae). [1-2] Antivenom is the definitive treatment, and early administration is associated with the best outcomes. [3] Contact Poison Control (1-800-222-1222) early for all cases. [1]
The following figure illustrates the progressive clinical manifestations of pit viper envenomation and the importance of antivenom over surgical intervention:
1. History
- Time of bite — delays >6 hours increase likelihood of severe systemic envenomation (LR 3.4) [4]
- Snake identification — species, size (larger snakes = higher venom load, LR 3.1 for severe envenomation), color, head shape; photograph if safe [3-4]
- Bite location — extremity vs. trunk/head/neck; hand and face bites are higher risk [5]
- Symptom progression — pain, swelling, paresthesias, nausea/vomiting, metallic taste, dizziness, syncope
- Prehospital interventions — tourniquets, suction, ice, incision (all potentially harmful and should be documented) [1-2]
- Number of bites and whether the snake was provoked
- Tetanus immunization status [3]
2. Alarm Features
- Rapidly progressive swelling beyond the bite site (mark leading edge with time stamps) [6]
- Hypotension (systolic BP <90 mmHg), severe tachycardia (HR >150), respiratory distress [6-7]
- Ptosis or cranial nerve deficits — suggests neurotoxic envenomation (Mojave rattlesnake, coral snake) [4][6]
- Active bleeding — gingival, epistaxis, hematuria, GI hemorrhage, or signs of DIC [5]
- Altered mental status, seizures, or focal neurologic deficits (concern for intracranial hemorrhage) [5]
- Airway compromise — tongue/pharyngeal swelling, especially with head/neck bites [7]
- Rhabdomyolysis — dark urine, severe myalgias [5]
- Anaphylaxis to venom itself (early-onset urticaria, angioedema, bronchospasm, shock) [8]
3. Medications
Antivenom (definitive treatment):
- CroFab (ovine Fab): Initial dose 4–6 vials IV over ≥1 hour; repeat 4–6 vials if initial control not achieved; then 2 vials q6h × 3 doses (18 hours) for maintenance [7]
- Anavip (equine F(ab')₂): Initial dose 10 vials IV over 60 minutes; repeat 10 vials as needed; then 4 vials as needed for re-emerging symptoms; observe ≥18 hours [9]
- Children require at least the same dose as adults (venom load is independent of body size) [3]
Medications to avoid or use with caution:
- Heparin — ineffective for venom-induced consumption coagulopathy (VICC) [3][6]
- Opioids — use cautiously if neurotoxic envenomation is suspected (coral snake, Mojave rattlesnake) to avoid masking neurologic signs [6]
- NSAIDs/aspirin — may worsen coagulopathy and bleeding risk
- Prophylactic antibiotics — not recommended; use only if clinical/microbiologic evidence of wound infection or necrosis [3][6]
- Corticosteroids, antihistamines, antifibrinolytics — lack evidence of effectiveness as routine adjuncts [8]
- FFP/blood products — administer only simultaneously with additional antivenom if clinically needed; giving FFP without antivenom adds substrate for unneutralized venom [3][6]
Supportive medications:
- Epinephrine and diphenhydramine should be at bedside for antivenom-related anaphylaxis [3]
- Tetanus prophylaxis as indicated [3]
- Analgesics (acetaminophen; opioids if not neurotoxic envenomation)
4. Diet
- NPO initially if moderate-to-severe envenomation (potential for surgical intervention, intubation, or clinical deterioration)
- Aggressive IV hydration — particularly with rhabdomyolysis or hypovolemic shock from third-spacing [6][8]
- No specific dietary triggers or long-term dietary management
5. Review of Systems
- Neurologic: Paresthesias (perioral, extremity), diplopia, ptosis, dysarthria, dysphagia, weakness, fasciculations, altered mental status [5]
- Hematologic: Gingival bleeding, epistaxis, hematuria, melena, petechiae, easy bruising [5]
- Cardiovascular: Chest pain, palpitations, syncope, lightheadedness [5]
- Respiratory: Dyspnea, tachypnea, respiratory distress [5]
- GI: Nausea, vomiting, abdominal pain, diarrhea [5]
- Musculoskeletal: Myalgias, muscle cramps, joint stiffness [5]
- Renal: Dark urine, decreased urine output [5]
6. Collateral History and Family History
- Witnesses — confirm snake identification, time of bite, circumstances
- Allergies — specifically to horse or sheep products (antivenom source animals) [6]
- Prior snakebites — previous antivenom exposure increases risk of hypersensitivity reactions [6]
- Captive/exotic snakes — nonnative species pose unique identification and antivenom sourcing challenges [3]
- Family history is generally not relevant unless there is a known bleeding diathesis
7. Risk Factors
- Age <12 years — increased likelihood of severe systemic envenomation (LR 2.9–3.2) due to smaller body mass relative to venom load [4]
- Large snake size — LR 3.1 for severe envenomation [4]
- Rattlesnake species (vs. copperhead/cottonmouth) — copperhead/cottonmouth bites are less likely to be severe (LR 0.28) [4]
- Delayed presentation (>6 hours) — LR 3.4 for severe systemic envenomation [4]
- Bite location — trunk, head, neck bites are higher risk [7]
- Tourniquet misuse — OR 15.45 for amputation risk [10]
- Outdoor activities — spring/summer/early fall, rural settings, hiking, gardening [1][11]
- Intentional handling of snakes (significant proportion of bites)
8. Differential Diagnosis
- Nonvenomous snakebite (dry bite) — 10–90% of bites by venomous snakes inject no venom [8]
- Insect or spider bite — brown recluse (necrotic wound), black widow (systemic symptoms)
- Cellulitis/abscess — if presenting late without witnessed bite
- Allergic reaction/anaphylaxis — from other cause
- Trauma — puncture wound with secondary infection
- Thrombotic microangiopathy from other causes (TTP/HUS) — if presenting with coagulopathy and AKI without clear bite history
- Unexplained coagulopathy — snake envenomation should be considered in the differential of otherwise unexplained coagulopathy, neuropathy, or abdominal pain [3]
9. Past Medical History
- Bleeding disorders or anticoagulant/antiplatelet use — increases hemorrhagic risk
- Chronic kidney disease — increased vulnerability to venom-induced AKI
- Cardiovascular disease — may not tolerate hemodynamic instability
- Prior snakebite and antivenom treatment — risk of serum sickness or anaphylaxis
- Immunocompromised state — increased infection risk from wound necrosis
- Pregnancy — fetal loss risk especially if bite occurs before 20 weeks; antivenom is used for the same indications as in nonpregnant patients [3]
10. Physical Exam
- Vital signs: Hypotension, tachycardia, tachypnea — signs of systemic envenomation [6]
- Bite site: Fang marks (may be single, obscured by edema, or appear as abrasion); erythema, edema, ecchymosis, blistering [3]
- Serial circumferential measurements at multiple points above and below the bite, repeated every 15–20 minutes; mark the leading edge of swelling with time [6]
- Neurologic exam: Ptosis, extraocular movement deficits, dysarthria, dysphagia, muscle weakness, fasciculations, altered sensorium [6]
- Skin: Petechiae, purpura, bleeding from IV sites or mucous membranes
- Compartment assessment: Tenseness, pain with passive stretch (though most swelling is subcutaneous, not true compartment syndrome) [6]
- Airway: Tongue/pharyngeal edema if head/neck bite
11. Lab Studies
Per the Wilderness Medical Society guidelines, the following should be obtained at baseline and serially: [5]
- CBC with platelets — thrombocytopenia (initial platelet <150K increases likelihood of severe hematologic effects, LR 3.7) [4]
- PT/INR, PTT — INR is most useful for coagulopathy assessment [5]
- Fibrinogen (measured, not calculated) — hypofibrinogenemia is the most specific marker (LR 5.1 for severe hematologic effects) [4]
- D-dimer — more sensitive for early coagulopathy detection [5]
- BMP — electrolytes, renal function (rhabdomyolysis, AKI)
- LFTs — hepatic dysfunction
- CK (total creatine kinase) — rhabdomyolysis
- Urinalysis — myoglobinuria, hematuria
- Type and screen — obtain early, though transfusion is rarely needed [5]
- Troponin — if chest pain present [5]
Serial labs: Repeat every 4–6 hours for minor envenomations; every 1 hour after antivenom until initial control for moderate/severe [5]
12. Imaging
- Ultrasound — useful for detecting retained fangs/teeth, edema location, and compartment assessment [3]
- Chest radiograph — if dyspnea, chest pain, or respiratory distress [5]
- CT head (noncontrast) — if neurologic deficits or concern for hemorrhagic CVA [5]
- CT abdomen or FAST ultrasound — if abdominal pain/distention or concern for intra-abdominal bleeding [5]
- MRI — may be used for compartment pressure assessment in select cases [3]
- Imaging is not routinely required for uncomplicated envenomations
13. Special Tests
- Snakebite Severity Score (SSS): 6 domains (pulmonary, cardiovascular, local wound, GI, hematologic, CNS); scores categorized as no effect (≤1), mild (2), moderate (3–7), severe (≥8). A change of 1 point has 97% sensitivity and 81% specificity for detecting clinical worsening. Note: this was developed as a research tool and has limitations for individual patient prognostication [4][8]
- Unified Severity Grading: [7]
- 20-minute whole blood clotting test (20WBCT) — bedside test for coagulopathy, particularly useful in resource-limited settings [3][8]
- Compartment pressure measurement — if suspected compartment syndrome (>30 mmHg is concerning) [6]
14. ECG
- Indications: Chest pain, dyspnea, hemodynamic instability, severe envenomation [5]
- Findings to watch for: Tachyarrhythmias, conduction defects, ST changes (myocardial damage from direct venom toxicity or stress cardiomyopathy) [8]
- Cardiac monitoring is recommended for moderate-to-severe envenomations
15. Assessment
- Severity stratification is dynamic — patients can progress from mild to severe over hours; close monitoring and serial reassessment are essential [4][8]
- Pooled prevalence of severe systemic envenomation is ~14%, severe tissue injury ~14%, and severe hematologic effects ~18% [4]
- Coral snake envenomation presents differently: minimal local findings but delayed neurotoxicity (up to 12 hours) with cranial nerve palsies, respiratory paralysis [6]
- Copperhead bites are generally less severe than rattlesnake bites but can still cause significant local tissue injury and coagulopathy [4]
- Complications: Tissue necrosis, compartment syndrome (rare), VICC, thrombotic microangiopathy, AKI, rhabdomyolysis, anaphylaxis to venom, serum sickness (post-antivenom), wound infection [3]
16. Treatment Plan
Prehospital:
- Move away from the snake; photograph if safe; do NOT attempt capture [1]
- Remove jewelry/constricting items; loosely splint the bitten extremity [3]
- Do NOT apply tourniquets, ice, suction, incision, or electric shock — all are ineffective or harmful [1-2]
- Rapid transport via EMS to a facility with antivenom capability [2]
Emergency Department:
- ABCs, IV access in unaffected extremity, continuous monitoring [3]
- Clean wound, inspect for retained fangs; update tetanus [3]
- Antivenom administration — initiate as soon as envenomation is confirmed:
- CroFab: 4–6 vials IV initially → repeat until initial control → 2 vials q6h × 18 hours [7]
- Anavip: 10 vials IV initially → repeat 10 vials as needed → 4 vials for re-emerging symptoms [9]
- Elevate the bitten extremity during and after antivenom infusion [3]
- Manage anaphylaxis to antivenom with epinephrine, antihistamines, and supportive care [3]
- Pain management: Acetaminophen, opioids as needed (avoid if neurotoxic envenomation suspected) [3][6]
- Coagulopathy: Antivenom is the primary treatment; blood products only with concurrent additional antivenom; heparin is ineffective [3][6]
- Compartment syndrome: Additional antivenom + elevation first; fasciotomy only as last resort if circulatory compromise persists despite antivenom (fasciotomy has not been shown to improve outcomes) [3][6]
- Neurotoxic envenomation (coral snake, Mojave rattlesnake): Airway management, mechanical ventilation if needed; anticholinesterase agents (neostigmine) may be effective for post-synaptic neurotoxicity in some elapid bites [8]
17. Disposition
- Coral snake bites: Observe for at least 12–24 hours even if asymptomatic due to delayed neurotoxicity [6][8]
- Specialist consultation: Poison Control (1-800-222-1222), medical toxicology, surgery (if compartment syndrome concern), critical care [1][4]
18. Follow Up / Return Precautions
- Outpatient labs: Repeat CBC, PT/INR, fibrinogen at 2–3 days and 5–7 days after last antivenom dose to evaluate for delayed or recurrent coagulopathy [5]
- Serum sickness: Occurs in ~5–20% of patients receiving antivenom, typically 7–21 days post-treatment; symptoms include fever, arthralgias, rash, lymphadenopathy; treat with oral corticosteroids and antihistamines [5]
- Activity restrictions: Avoid contact sports, dental extractions, tattoos/piercings, and elective surgery for at least 2 weeks [5]
- Return immediately for: Worsening swelling, new bleeding (gums, urine, stool), bruising, fever, wound infection signs, difficulty breathing, weakness, or any neurologic symptoms [5]
- Expected recovery: Most patients with mild-to-moderate envenomation recover fully; local swelling may take days to weeks to resolve; early rehabilitation is important to minimize residual disability [8]
- Wound care: Follow up for wound checks, especially if necrosis was present (infection risk) [3]
References
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