Overview
Snake Bite
Quick Reference
Critical Alerts
- 20-25% of snake bites are "dry bites" - no envenomation
- Antivenom is the definitive treatment for moderate-severe envenomation
- Do NOT apply tourniquet, incise, or suck wound - causes more harm
- Progressive swelling indicates envenomation - may need antivenom
- Coagulopathy can be delayed and recurrent - monitor for days
Key Diagnostics
- Serial examinations (mark swelling progression)
- CBC, PT/INR, fibrinogen
- BMP, CK (renal function, rhabdomyolysis)
- Type and screen
- Wound exam (fang marks, necrosis)
Emergency Treatments
- Immobilize extremity at heart level
- IV access and fluids
- Antivenom: CroFab for North American pit vipers (4-6 vials initially)
- Tetanus prophylaxis
- Pain control: Opioids as needed
- Avoid anticoagulants, NSAIDs, aspirin
Definition
Snake bite envenomation occurs when a venomous snake injects venom through its fangs during a bite. Severity depends on snake species, amount of venom injected, bite location, and patient factors. Emergency management focuses on supportive care and antivenom administration.
Venomous Snake Families
North America
| Family | Examples | Venom Type |
|---|---|---|
| Crotalidae (Pit Vipers) | Rattlesnakes, Cottonmouths, Copperheads | Cytotoxic, hemotoxic |
| Elapidae | Coral snakes | Neurotoxic |
Other Regions
| Region | Notable Snakes | Venom Type |
|---|---|---|
| Australia | Taipans, Brown snakes, Tiger snakes | Neurotoxic, hemotoxic |
| Asia | Cobras, Kraits, Russell's viper | Neurotoxic, hemotoxic |
| Africa | Mambas, Puff adder, Saw-scaled viper | Neurotoxic, hemotoxic |
| South America | Fer-de-lance, Bushmaster | Hemotoxic |
Epidemiology
- US incidents: ~7,000-8,000 venomous bites/year
- Deaths (US): 5-10 per year
- Worldwide: 5 million bites, 100,000 deaths annually
- Age/Sex: Young males most common (handling, outdoor activities)
Pathophysiology
Venom Composition
Pit Viper Venom (Crotalid)
| Component | Effect |
|---|---|
| Metalloproteinases | Tissue destruction, hemorrhage |
| Phospholipase A2 | Myonecrosis, hemolysis |
| Serine proteases | Coagulopathy (consumes fibrinogen) |
| Hyaluronidase | Tissue spread ("spreading factor") |
Elapid Venom (Coral Snake, Cobras)
| Component | Effect |
|---|---|
| Neurotoxins (α-neurotoxins) | Postsynaptic neuromuscular blockade |
| Phospholipase A2 | Presynaptic neurotoxicity |
| Cardiotoxins | Myocardial damage (some species) |
Mechanism of Injury
Crotalid Envenomation
Venom injection
↓
Local tissue destruction (proteases)
↓
Increased vascular permeability → Edema
↓
Hemorrhage (vascular damage)
↓
Consumption of clotting factors → Coagulopathy
↓
Systemic effects: Hypotension, DIC, rhabdomyolysis
Elapid Envenomation
Venom injection
↓
Neurotoxin binds to neuromuscular junction
↓
Blocks acetylcholine transmission
↓
Descending paralysis (begins with cranial nerves)
↓
Respiratory failure
Dry Bites
- 20-25% of venomous snake bites inject no venom
- Still need observation
- Cannot be determined immediately
Clinical Presentation
Pit Viper Envenomation (Crotalid)
Local Effects
| Finding | Timing |
|---|---|
| Fang marks (1-2) | Immediate |
| Pain (usually severe) | Immediate |
| Edema | Within 30-60 min, progressive |
| Ecchymosis | Hours |
| Hemorrhagic bullae | Hours-days |
| Tissue necrosis | Days |
Systemic Effects
| Finding | Significance |
|---|---|
| Nausea, vomiting | Common |
| Metallic taste | Characteristic |
| Perioral tingling | Systemic absorption |
| Hypotension | Severe envenomation |
| Coagulopathy | Bleeding, DIC |
| Rhabdomyolysis | Some species (especially Mojave) |
Coral Snake Envenomation (Elapid)
Different Pattern
| Finding | Timing |
|---|---|
| Minor pain/swelling | Immediate |
| Ptosis, diplopia | 2-6 hours |
| Dysphagia, dysarthria | Hours |
| Respiratory paralysis | Hours to 24h |
| Nausea, vomiting | Common |
Warning: Coral snakes have small mouths; may not leave visible fang marks
Grading Severity (Pit Vipers)
| Grade | Local Findings | Systemic Findings | Coagulopathy |
|---|---|---|---|
| Minimal (Dry bite) | Fang marks only, no swelling | None | None |
| Mild | Swelling at bite site, <2 joints | None | None |
| Moderate | Swelling beyond 1 joint | Non-life-threatening | Mild |
| Severe | Extensive swelling, necrosis | Hypotension, bleeding | Significant |
Minimal local effects initially
Common presentation.
Onset delayed (hours)
Common presentation.
Progressive neurotoxicity
Common presentation.
Red Flags (Life-Threatening)
Critical Presentations
| Red Flag | Concern | Action |
|---|---|---|
| Rapidly progressing edema | Severe envenomation | Antivenom immediately |
| Coagulopathy (PT/fibrinogen abnl) | Hematologic toxicity | Antivenom |
| Hypotension | Severe envenomation | Fluids, antivenom, vasopressors |
| Respiratory distress (elapid) | Neurotoxicity | Airway management, antivenom |
| Altered mental status | Severe envenomation | Full resuscitation |
| Ptosis, dysphagia (coral) | Neurotoxic progression | Antivenom, prepare airway |
| Angioedema/anaphylaxis | To venom or antivenom | Standard anaphylaxis treatment |
Airway Compromise
Coral Snake/Elapid
- Progressive weakness
- Bulbar symptoms
- Respiratory failure
- May need prolonged mechanical ventilation
Differential Diagnosis
Other Causes of Bite/Sting
| Condition | Features |
|---|---|
| Non-venomous snake | No envenomation syndrome |
| Spider bite | Different puncture pattern |
| Insect sting | Usually obvious history |
| Scorpion sting | Different syndrome |
| Marine envenomation | Water exposure |
| Infection (cellulitis) | No bite history, later presentation |
Mimics of Envenomation
- Allergic reaction
- Thrombophlebitis
- Compartment syndrome
- Deep vein thrombosis
- Fracture
Diagnostic Approach
Initial Assessment
Key History
- Time of bite
- Snake identification if possible (do NOT attempt to catch)
- Photo of snake helpful
- Location of bite
- First aid measures taken
- Symptoms and progression
Physical Examination
Essential Documentation
- Mark extent of swelling with time
- Serial measurements (circumference)
- Vital signs
- Neuromuscular function
- Complete skin exam
- Signs of bleeding
Laboratory Studies
| Test | Purpose | Timing |
|---|---|---|
| CBC | Hemolysis, thrombocytopenia | Baseline, Q4-6h |
| PT/INR, aPTT | Coagulopathy | Baseline, Q4-6h |
| Fibrinogen | Consumption | Baseline, Q4-6h |
| BMP | Renal function | Baseline |
| CK | Rhabdomyolysis | Baseline, Q6h |
| Type and Screen | Transfusion prep | If moderate-severe |
| Urinalysis | Myoglobinuria | If CK elevated |
Snake Identification
Pit Vipers (Crotalidae)
- Triangle-shaped head
- Vertical "cat-eye" pupils
- Heat-sensing pit between eye and nostril
- Rattles (rattlesnakes only)
Coral Snakes
- Red, yellow, black bands
- "Red on yellow, kill a fellow; red on black, venom lack" (North America only)
- Small, round head
Treatment
Field Management
Do NOT:
- Apply tourniquet
- Incise wound
- Attempt to suck out venom
- Apply ice
- Apply electric shock
- Delay transport to hospital
DO:
- Keep patient calm
- Immobilize affected extremity
- Remove jewelry/constrictive items
- Transport to hospital rapidly
- Photo of snake if safely possible
Emergency Department Management
Initial Steps
1. Assess ABC, IV access, monitoring
2. Establish IV in unaffected extremity
3. Mark extent of swelling with time
4. Pain control (opioids)
5. Tetanus prophylaxis
6. Labs (CBC, coags, BMP, CK)
7. Contact poison control (1-800-222-1222)
Antivenom Therapy
Crotalidae Polyvalent Immune Fab (CroFab)
Indications:
- Progressive local swelling
- Systemic symptoms (hypotension, bleeding)
- Coagulopathy (elevated PT, low fibrinogen)
Dosing:
Initial: 4-6 vials IV (diluted in NS, infuse over 60 min)
Reassess in 1 hour
If control achieved:
- Maintenance: 2 vials q6h x 3 doses (18 hours total)
If not controlled:
- Repeat 4-6 vials, reassess
- May need additional doses
Monitoring for Reaction
- Start infusion slowly (25-50 mL/hr first 10 min)
- Watch for anaphylaxis, serum sickness
- Have epinephrine ready
Anavip (Alternative)
- Crotalidae Immune F(ab')2 (horse-derived)
- 10 vials initial dose
- Different pharmacokinetics
Coral Snake Antivenom
North American Coral Snake Antivenom
- May be in limited supply
- Contact poison control
- Consider prophylactic antivenom even without symptoms (delayed onset)
Supportive Care
| Issue | Management |
|---|---|
| Pain | Opioids; avoid NSAIDs (coagulopathy) |
| Hypotension | IV fluids, vasopressors if refractory |
| Coagulopathy | Antivenom first; FFP/platelets if severe bleeding |
| Rhabdomyolysis | IV fluids, monitor CK, renal function |
| Compartment syndrome | Measure compartment pressures; fasciotomy rarely needed if antivenom given |
| Wound care | Clean, tetanus; antibiotics not routinely needed |
Fasciotomy Considerations
- Rarely needed with adequate antivenom
- Venom is in subcutaneous tissue, not compartments
- Measure compartment pressures before fasciotomy
- Consult with toxicologist and surgeon
Disposition
Admission Criteria
Admit for:
- Any coagulopathy
- Moderate-severe envenomation
- Antivenom administration
- Coral snake bite (may need prolonged observation)
- Progressive symptoms
Observation Period
| Scenario | Duration |
|---|---|
| Pit viper, no symptoms after 8-12h | Consider discharge |
| Pit viper with mild symptoms | 24h minimum |
| Received antivenom | 24h + coag monitoring |
| Coral snake | 24h minimum (onset may be delayed) |
Recurrent Coagulopathy
- Can occur days after initial treatment (CroFab)
- Schedule follow-up labs at 2-4 days and 1 week
- Repeat antivenom if needed
- Avoid surgery, dental procedures, contact sports for 2 weeks
Discharge Instructions
- Wound care
- Elevate extremity
- Return for: increased swelling, bleeding, fever, breathing problems
- Follow-up labs scheduled
- Avoid NSAIDs, aspirin, anticoagulants
- Activity restrictions
Patient Education
Understanding Snake Bites
- Not all bites result in envenomation
- Antivenom is the main treatment for significant bites
- Recovery may take days to weeks
- Blood clotting problems can recur - follow-up labs essential
Prevention
- Wear boots and long pants in snake habitat
- Watch where you step and put your hands
- Don't handle snakes (even "dead" ones)
- Avoid walking in tall grass or at night in snake areas
- Use flashlight at night outdoors
When to Return
- Worsening swelling
- Bleeding from gums, nose, or wound
- Black/blue discoloration spreading
- Difficulty breathing
- Fever
- Numbness or weakness
Special Populations
Pediatric
- Same antivenom dosing as adults (mg of venom, not patient size)
- Volume of distribution considerations
- May appear more toxic (smaller size, same venom)
Pregnancy
- Antivenom is indicated if envenomation present
- Fetal monitoring required
- Obstetric consultation
Pre-existing Coagulopathy
- Higher risk with envenomation
- May need to hold anticoagulation
- Closer monitoring
Allergic to Antivenom
- Skin testing not reliable
- Premedicate with antihistamines, steroids
- Infuse slowly
- Treat anaphylaxis if occurs
- Benefits usually outweigh risks in severe envenomation
Quality Metrics
Performance Indicators
| Metric | Target |
|---|---|
| Time to first labs | <60 min |
| Antivenom for moderate-severe | <2 hours |
| Poison control consulted | 100% envenomations |
| Serial swelling documentation | Q1h initially |
| Tetanus prophylaxis | 100% |
| Follow-up labs scheduled | 100% for any coagulopathy |
Documentation Requirements
- Time of bite
- Snake description/identification
- Progression of swelling (with markings and times)
- Vital signs
- Lab values and trends
- Antivenom dose and timing
- Any adverse reactions
- Disposition and follow-up plan
Key Clinical Pearls
Diagnostic Pearls
- 20-25% are dry bites - observe before committing to antivenom
- Mark and time swelling - progression guides treatment
- Coagulopathy may be delayed - repeat labs at 6h even if initial normal
- Coral snakes have delayed symptoms - admit even if asymptomatic
- Don't rely on fang marks - may be subtle or absent
Treatment Pearls
- Antivenom is the definitive treatment - don't delay for severe
- Avoid NSAIDs and anticoagulants - worsen bleeding
- Fasciotomy rarely needed - give antivenom first
- Whole blood/FFP not substitutes for antivenom
- Recurrent coagulopathy is common - schedule follow-up labs
Disposition Pearls
- 8-12 hour observation for pit viper if no symptoms
- 24 hours for any envenomation or antivenom use
- Coral snakes = 24h minimum regardless of symptoms
- Follow-up at 2-4 days and 1 week for coags
- Poison control (1-800-222-1222) is essential resource
References
- Lavonas EJ, et al. Unified treatment algorithm for the management of crotaline snakebite in the United States. BMC Emerg Med. 2011;11:2.
- Seifert SA, et al. North American snake envenomation. Infect Dis Clin North Am. 2012;26(4):821-841.
- Dart RC, et al. A randomized multicenter trial of crotalinae polyvalent immune Fab for crotalid snakebite. Arch Intern Med. 2001;161(16):2030-2036.
- Gold BS, et al. Bites of venomous snakes. N Engl J Med. 2002;347(5):347-356.
- Corneille MG, et al. Management of venomous snakebites: Update for 2019. Trauma Surg Acute Care Open. 2020;5(1):e000445.
- Ruha AM, et al. Crotalinae Fab antivenom. Clin Toxicol. 2012;50(1):17-24.
Version History
| Version | Date | Changes |
|---|---|---|
| 1.0 | 2025-01-15 | Initial comprehensive version with 14-section template |