Recommended Clinical Assessments and Laboratory Tests for Snake Bite Investigation
The initial assessment of a snake bite should include a pressure immobilization bandage (except for North American pit vipers), immobilization of the affected limb, and immediate contact with emergency services, followed by comprehensive laboratory testing including complete blood count, coagulation studies, and renal function tests to guide antivenom administration. 1
Initial Clinical Assessment
History
- Time and circumstances of the bite
- Description of the snake (if possible)
- Symptoms since the bite (pain, swelling, bleeding, neurological symptoms)
- First aid measures already applied
- Medical history (especially coagulation disorders, allergies)
Physical Examination
- Vital signs (blood pressure, heart rate, respiratory rate, oxygen saturation)
- Bite site examination:
- Fang marks
- Local tissue damage
- Extent of swelling and ecchymosis
- Measurement and marking of swelling boundaries for monitoring progression
Neurological Assessment
- Level of consciousness
- Cranial nerve function (especially for neurotoxic envenomation)
- Motor strength
- Sensory function
- Signs of neurotoxicity:
- Ptosis
- Ophthalmoplegia
- Bulbar weakness
- Respiratory muscle weakness
Laboratory Testing
Essential Laboratory Tests
- Complete blood count (CBC)
- Coagulation studies:
- Prothrombin time (PT)
- Activated partial thromboplastin time (aPTT)
- International normalized ratio (INR)
- Fibrinogen level
- D-dimer
- Renal function tests:
- Blood urea nitrogen (BUN)
- Creatinine
- Electrolytes
- Creatine kinase (for rhabdomyolysis)
- Urinalysis (for myoglobinuria, hematuria)
- Type and cross-match (in case blood products are needed)
Specific Venom Detection
- Enzyme immunoassay for venom antigen detection (where available) 2
- This can help identify the specific snake species when it remains unidentified
Monitoring Parameters
Cardiovascular Monitoring
- Continuous cardiac monitoring
- Blood pressure monitoring
- Oxygen saturation
Coagulation Monitoring
- Simple bedside clotting test (20-minute whole blood clotting test)
- Place 2-3 mL of venous blood in a clean, dry glass tube
- Leave undisturbed for 20 minutes
- Tilt to assess for clot formation
- Failure to clot indicates coagulopathy 3
Progression Monitoring
- Serial measurements of limb circumference at the bite site
- Repeat coagulation studies every 6 hours initially
- Monitor for development of compartment syndrome
- Continuous monitoring for signs of systemic envenomation
Special Considerations
For Suspected Neurotoxic Envenomation
- More frequent neurological assessments
- Respiratory function tests:
- Peak flow measurements
- Forced vital capacity
- Negative inspiratory force
For Suspected Hemotoxic Envenomation
- More frequent coagulation studies
- Monitor for signs of bleeding (gums, IV sites, wounds)
- Monitor for thrombotic microangiopathy (TMA) 4
Antivenom Considerations
- Determine need for antivenom based on:
- Evidence of systemic envenomation
- Progression of local symptoms
- Laboratory abnormalities
- Prepare for potential allergic reactions:
- Have epinephrine, antihistamines, and corticosteroids available
- Consider premedication with antihistamines and corticosteroids 5
Common Pitfalls to Avoid
Delayed recognition of systemic envenomation: Monitor for subtle signs of systemic toxicity even when local symptoms appear mild.
Inappropriate use of tourniquets: Do not apply tourniquets as they may worsen tissue damage.
Application of suction: Avoid suction devices as they are ineffective and may cause harm 1.
Applying ice: Do not apply ice to snake bites as this may worsen tissue damage.
Failure to repeat laboratory tests: Coagulopathy may develop hours after the bite, necessitating serial testing.
Missing compartment syndrome: Regular assessment of neurovascular status is essential.
Species misidentification: When possible, safely photograph or identify the snake to guide specific antivenom selection, but never delay treatment to identify the snake.
By following this comprehensive approach to snake bite assessment and monitoring, clinicians can effectively diagnose envenomation, track its progression, and guide appropriate treatment decisions including antivenom administration.