Snake Bite - Complete Clinical Overview

Overview

• Hemotoxic (most vipers/pit vipers/Crotalids) - coagulopathy, local tissue destruction
• Neurotoxic (Elapids - cobras, kraits, mambas, coral snakes, sea snakes) - neuromuscular paralysis
• Cytotoxic/Myotoxic - local tissue necrosis, rhabdomyolysis
• Mixed - combinations of the above

1. History Collection

Basic Incident History

• Time of bite - exact time, to calculate time elapsed before treatment
• Location of bite on the body (hand, foot, leg, face)
• Geographic location where it occurred (water, field, jungle, urban)
• Snake identification - color, size, shape of head (triangular vs round), pattern (bands, spots), presence of rattle, pit behind eye
• Number of bites received
• Did the snake appear aggressive or was it provoked? (up to 60% of bites occur during deliberate provocation)

First Aid Already Rendered

• Was a tourniquet applied? (important - tourniquets are contraindicated for Crotalid/pit viper bites as they concentrate venom, increase local necrosis)
• Was incision/suction done? (historically used, now not recommended since 1980)
• Was ice or compression applied?
• Any electrical shock therapy? (ineffective and harmful)
• Pressure immobilization bandage applied? (appropriate for Elapid bites in Australia/Asia, not routine for pit vipers)
• Was the wound washed? (important: if a venom detection kit will be used, do not wash the wound)

Symptom Timeline

• Onset and progression of local symptoms: pain, swelling, bruising, blistering
• Systemic symptoms: nausea/vomiting, metallic taste in mouth, perioral paresthesia, muscle twitching, difficulty swallowing, drooping eyelids, blurred vision, shortness of breath, dark urine, decreased urine output
• Rate of spread of ecchymosis - progression >10 cm/hour is an indication for antivenom

Past Medical History

• Allergies (especially horse/sheep serum - relevant for antivenom)
• Previous snakebite and antivenom use (sensitization risk)
• Bleeding disorders, medications (anticoagulants)
• Tetanus immunization status

2. Clinical Examination

General Assessment (ABCDE Approach)

• Airway and breathing - signs of respiratory paralysis (neurotoxic envenomation)
• Circulatory status - blood pressure, pulse, shock, hypotension
• Consciousness level - agitation, confusion (neurotoxic)

Vital Signs

• Blood pressure, heart rate, respiratory rate, temperature, SpO2

Local Examination (Bite Site)

• Fang mark(s) - document location, number, distance between marks (indicates snake size)
• Edema - measure circumference of affected limb and document baseline; re-measure serially
• Ecchymosis - mark the advancing border with a pen and write the time to monitor progression
• Blistering / vesicles / bullae
• Necrosis / tissue sloughing
• Lymphadenopathy in draining lymph nodes
• Pain, tenderness, warmth

Systemic Examination

3. Grading of Envenomation Severity

• Sabiston Textbook of Surgery, p. 879

4. Investigations

Immediate (Baseline + 1 hour post-removal of first aid, then at 6 and 12 hours)

• CBC with platelet count - thrombocytopenia indicates platelet consumption
• Prothrombin time (PT) and INR
• Activated partial thromboplastin time (aPTT)
• Fibrinogen level
• D-dimer and fibrin degradation products (FDP)
• Blood film - for haemolysis (fragmented red cells)

• Blood urea nitrogen (BUN) and serum creatinine - renal function
• Electrolytes (hyponatraemia seen with some envenomations)
• Creatine phosphokinase (CPK/CK) - for myotoxicity/rhabdomyolysis
• Liver function tests
• Blood glucose

• Urinalysis - haematuria, haemoglobinuria, myoglobinuria (tea/cola-coloured urine = myoglobinuria from rhabdomyolysis)
• Urine output monitoring (catheterise if needed)

• ECG - continuous cardiac monitoring; arrhythmias may occur with severe envenomation

• Wound swab if infection suspected

• Snake Venom Detection Kit (SVDK) - available in Australia and Papua New Guinea; swab the wound or test urine to identify venom immunotype (helps select monovalent antivenom). Important: do NOT wash the wound if SVDK will be used
• Chest X-ray if respiratory compromise or pulmonary oedema suspected

What the Results Tell You

• Procoagulant coagulopathy: prolonged PT/aPTT, high INR, raised D-dimer/FDP, low fibrinogen = venom-induced consumption coagulopathy
• Anticoagulant coagulopathy: abnormal PT/aPTT, high INR, but normal fibrinogen and D-dimer
• Rhabdomyolysis: grossly elevated CK, myoglobin in urine
• Renal damage: elevated creatinine, reduced urine output
• Haemolytic-uraemic syndrome pattern: thrombocytopenia + anaemia + intravascular haemolysis
• Tintinalli's Emergency Medicine, p. 1403

5. Treatment

Pre-Hospital / Field First Aid

• Remove all jewellery and tight clothing from the affected limb (anticipate swelling)
• Immobilize the bitten extremity in a functional position (like a splint)
• Keep the patient calm and limit exertion (walking increases lymphatic spread)
• Transport urgently to a medical facility with antivenom
• In Australia/New Guinea (Elapid endemic areas): apply pressure immobilization bandage - wrap elastic bandage firmly from the bite site upward to cover the entire limb (similar pressure to a sprain bandage, ~55 mmHg), then splint the limb. This retards lymphatic spread of neurotoxic venom.
• Outside Australia, for unidentified snakes or non-neurotoxic species: immobilization only (no pressure bandage, as it can worsen local necrosis from cytotoxic venom)

• Do not incise or suck the wound (outdated, increases infection, extracts minimal venom)
• Do not apply tourniquets (concentrates venom in limb, worsens necrosis - especially for pit viper bites)
• Do not apply ice or heat (no benefit)
• Do not give aspirin (worsens bleeding)
• Do not try to catch or handle the snake (risk of second bite)
• Do not use electrical shock therapy (proven ineffective)
• Do not apply cryotherapy (associated with high amputation rates)

Emergency Department Management

1. Secure IV access (two large-bore IV lines)
2. Baseline vital signs and continuous monitoring
3. Mark the advancing border of ecchymosis with a pen and note the time
4. Measure limb circumference at and above the bite site - re-measure every 15-30 min
5. If pressure bandage was applied, maintain it until envenomation is excluded or until antivenom is running
6. Do not remove first aid until antivenom is available and ready to infuse

• Clean the wound gently
• Tetanus toxoid/immunoglobulin as appropriate
• Prophylactic antibiotics are NOT routinely recommended (infection is surprisingly uncommon; if infection is confirmed by culture, treat with appropriate antibiotics covering Pseudomonas, Enterobacteriaceae, Staphylococcus, Clostridia)
• Steroids have no proven benefit for venom effects (but useful for anaphylaxis or serum sickness after antivenom)

• Dry bite (no envenomation): observe for 4-6 hours (longer for Elapid bites, as local signs may be minimal while systemic toxicity develops)
• Evidence of envenomation: admit to a monitored bed for at least 24 hours

Antivenom Therapy

• Any sign of systemic envenomation (coagulopathy, neurotoxicity, haemolysis, myotoxicity, hypotension)
• Rapidly advancing ecchymosis (>10 cm/hour)
• Moderate or severe grade envenomation
• Early antivenom is especially important for AKI post-snakebite ("Early administration of antivenom is vital; delay results in..." worse outcomes - Brenner and Rector's The Kidney)

• Treatment dose is NOT based on body weight - it is based on the amount of venom injected (which is the same regardless of patient size; children and adults receive the same dose)
• Antivenom must be given IV (not IM)
• Pre-treat with adrenaline (epinephrine) SC/IM if anaphylaxis risk is high
• Monitor for anaphylaxis during infusion

• CroFab (Crotalidae Polyvalent Immune Fab - Ovine): used in USA for pit viper bites; derived from sheep immunized with venom from 4 species; Fab fragments; lower anaphylaxis risk than old horse serum
• ANAVIP (Crotalidae Immune F(ab')2 - equine): longer half-life, may reduce late coagulopathy; equine origin - caution in horse-allergic patients
• Polyvalent antivenom: used in many countries for broad snake coverage
• Monovalent antivenom: species-specific; selected based on SVDK results in Australia

• Coagulopathy can recur up to 2 weeks after initial treatment
• Serum sickness may develop days later (treat with steroids)

Other Medical Management

6. How to Write the Diagnosis

Format:

[Type of envenomation] by [identified/unidentified snake species] - [Grade/Severity] - [Complications]

Examples:

Snakebite envenomation (unidentified species), right lower limb - Grade 2 (moderate) - with local hemotoxic features

Viper envenomation (Vipera russelli / Russell's viper), right hand - Grade 3 (severe) - complicated by:

• Venom-induced consumption coagulopathy (VICC)
• Acute kidney injury
• Local tissue necrosis

Cobra (Naja sp.) envenomation, left index finger - Grade 3 (severe) - with neurotoxic features (bilateral ptosis, bulbar palsy, impending respiratory failure)

Suspected snakebite (dry bite / non-envenomation), left foot - no evidence of local or systemic envenomation

Components of the Written Diagnosis Include:

1. Snakebite / Envenomation - confirmed or suspected
2. Snake type - if identified (species name or family); if not, state "unidentified snake"
3. Site - anatomical location of bite
4. Severity grade - Grade 0-3
5. Venom type - hemotoxic / neurotoxic / cytotoxic / myotoxic
6. Complications - list each one (AKI, coagulopathy, necrosis, respiratory failure, etc.)
7. Treatment status - "post-antivenom" or "on antivenom therapy" if relevant

Quick Reference Summary Table

• Sabiston Textbook of Surgery: The Biological Basis of Modern Surgical Practice, Chapter 44
• Tintinalli's Emergency Medicine: A Comprehensive Study, Chapter 213
• Brenner and Rector's The Kidney, Chapter on AKI
• Mulholland and Greenfield's Surgery: Scientific Principles and Practice - 7e