Snakebite

Objectives

To provide an evidence-based approach to management of snakebite in the operational environment.

Scope

From point of bite first aid to prolonged management in deployed hospital care.

Audience

This guideline is intended for the use of registered healthcare professionals fulfilling a general role in forward medical locations or in an Emergency Department on deployed operations.

Initial Assessment & Management

First Aid + Initial Management

Ensure scene safety, do not attempt to kill snake. 

• If available and can be safely obtained ask for a photograph or description of the offending snake. This information should accompany the patient to hospital to aid identification of snake species and antivenom dosing.

Routine resuscitation: MARCH

• Gain venous access in easily compressible locations: spontaneous haemorrhage from venous access sites can occur in haemotoxic envenomation.
• Treat early anaphylaxis with adrenaline. LINK to anaphylaxis guideline

Lay the patient flat. Splint and keep the bitten limb still. Remove rings and constrictive jewellery. 

Apply pressure pad dressing unless a neurotoxic snakebite can be definitively excluded. Pressure pad dressing should not be removed until arrival at a resuscitation facility with antivenom available. 

• Pressure pad: Apply a firm pad (eg multiple layers of cotton gauze or a firm rubber pad) and compress directly over the bite site using elasticated compression dressing.  
• Note: there are no UK native snakes with neurotoxic venom and therefore pressure-immobilisation is not required here. 

Do NOT:

Apply tourniquet.
Cut wound.
Wash or irrigate wound.
Suck/squeeze wound in attempt to encourage bleeding.
Apply cold/heat stimulus.

 Provide calm reassurance: snakebites often trigger significant anxiety which can mimic signs of systemic envenoming. 

Manage pain

   Avoid NSAIDs which may increase bleeding risk.

•    Avoid opioids in cases of neurotoxic envenoming which may increase respiratory depression. 
•    Avoid intramuscular injections

Assess for signs of systemic envenoming:

Note that up to  60% of bites by venomous snakes are ‘dry bites’ and do not result in envenoming. Onset of signs of envenoming may be delayed and therefore all patients should be observed for 24 hours before envenoming can be excluded. 

• Neurotoxic: bilateral ptosis/ophthalmoplegia, descending paralysis, dyspnoea, progressing to life threatening respiratory paralysis. 
  
  
• Haemotoxic: local bleeding from the bite site, spontaneous bleeding from venepuncture sites, systemic bleeding (gums, nose, GI/GU), coagulopathy
  
  
• Cytotoxic: severe local pain, rapidly progressing limb swelling and oedema, tissue destruction.
  
  
• Search for local lymphadenitis which may be the first sign of venom absorption.
  
  
• Seek early expert help via the ID reach back service in all cases where signs of envenoming are present

All patients should be evacuated to a facility with the ability to deliver antivenom 

Assess tetanus risk and give tetanus prophylaxis if required. 

Venom ophthalmia: spitting of venom into the eyes by any snake should be treated initially with copious fluid irrigation. Administration of topical anaesthetic drops may be required to overcome pain and facilitate irrigation. 

Record keeping

• EpiNATO-2: Serial Mike (Bites and Stings)
• Submit an FMed 85 notification to the Defence Public Health Unit

Advanced Assessment & Management

Reassess and resuscitate

All patients with snakebite should be monitored closely for signs of systemic envenoming and indications for antivenom administration. Signs of envenoming may be delayed and therefore patients must be observed for at least 24 hours.

Do not remove pressure pad until initial resuscitation complete, IV access established and antivenom available.

If available, the following investigations should be conducted in all patients:  

• FBC, U+Es, CK, LFTs, glucose, PT, APTT, group and save, urinalysis and ECG.
• If laboratory clotting studies are not available, perform a 20-minute whole blood clotting test (WBCT) to identify coagulopathy: place a few millilitres of venous blood into a clean dry glass test tube (plastic liable to cause false positive results). Leave it undisturbed for 20 minutes at ambient temperature. Unclotted blood that runs out or a friable clot that readily breaks down on tipping the tube once at 20 minutes indicates a possible clotting disorder. 
• Laboratory clotting studies or WBCT should be repeated after 6 hours. 
  
  

Assess for indications for antivenom administration. Antivenom is not always required. Patients may have been bitten by non-venomous snakes or may have a ‘dry bite’. Indications for antivenom: 

• Haemostatic abnormalities: spontaneous bleeding, positive WBCT, INR >1.2, PT >4-5s, Plt <100
• Neurotoxic signs: ptosis, external ophthalmoplegia, paralysis 
• Cardiovascular abnormalities: hypotension, shock, arrhythmia, abnormal ECG 
• AKI: oliguria/anuria, rising creatinine/urea
• Haemoglobin/myoglobin-uria
• Rapid extension of swelling beyond wrist/ankle within hours.
• Local swelling involving more than half the bitten limb within 12-24hr. 
• Rapid development of severe pain and swelling afer bites on the digits.

Antivenom administration

Antivenom dose is based on likely dose of venom and not patient size or weight, therefore children and adults require the same dose.

• Antivenom dosing is based on the likely biting species. Initial dosing will commonly require several vials of antivenom. Guidelines for antivenom doses can be provided by the Military Bites and Stings Working Group prior to deployment where antivenom is procured.
  
  Manufacturers dosing recommendations are unreliable and should not be used. 
• Consider pre-treatment with adrenaline to help prevent anaphylaxis (eg in situations where identification and treatment of anaphylaxis may be difficult; patients with history of anaphylaxis to antivenom) 

Adults: 250mcg SC (0.25ml 1:1000)

Children: 0.005mg/kg SC

• Be prepared to treat anaphylaxis with adrenaline. LINK to anaphylaxis guideline

Response to antivenom. 

• Neurotoxicity is the most urgent indication for antivenom – only very early (within 1 hour) administration of antivenom may prevent respiratory paralysis. Response may take hours or days to improve and respiratory support may still be required. 
• Cardiovascular effects such as hypotension and arrhythmia may improve within 10-20 minutes.
• Spontaneous bleeding usually resolves within 15-30 minutes and coagulopathy on laboratory tests or WBCT within 6 hours. 
• Antivenom cannot reverse established local tissue destruction but may limit further tissue damage. 

• Persistence or recurrence of spontaneous bleeding after 3 hours
• Recurrence of shock after 1 hour 
• Coagulopathy on WBCT or laboratory test after 6 hours
• Note that repeat doses of antivenom are not indicated in patients with neurotoxic bites who have already progressed to respiratory paralysis requiring ventilation.

Antivenom reactions.

• Anaphylaxis to antivenom components may occur in up to 10% of administrations. Typical onset is within 30 minutes of starting the antivenom infusion. Treat conventionally following anaphylaxis guidelines. LINK to anaphylaxis guideline. 
• Pyrogenic reactions occur commonly, with a typical onset 1-2 hours after antivenom administration with fever, rigors and hypotension. These reactions should be treated with antipyretics and cooling. 
• Late serum sickness typically occurs 5-10 days following antivenom administration, presenting with urticaria, arthralgia, fever, and lymphadenopathy. Treat with a 5-day course of prednisolone (20mg OD for adults; 0.7mg/kg OD for children). Antihistamines can also be used supportively for mild symptoms. 

Supportive management 

Wound management:

Assess tetanus risk and give tetanus prophylaxis if required. 

Wounds should be cleaned and irrigated. Blisters should be left intact.

Necrotic tissue should be reviewed by a surgeon and considered for debridement. Note that superficial skin appearances may be deceptive with subcutaneous tissue necrosis undermining apparently normal skin. 

Antibiotics are not indicated unless there are clear signs of infection or there is marked tissue necrosis. 

Severe local envenoming may result in features that mimic compartment syndrome, but on testing intra-compartmental pressures are usually not diagnostic of compartment syndrome which is a very rare complication of snakebite. Fasciotomy should only be considered after measurement of compartment pressures and early expert discussion via the ID reach back service is recommended. 

Neurotoxicity: 

Airway protection and respiratory support may be required usually for a period of a few days prior to recovery. 

Coagulopathy:

• Spontaneous bleeding should resolve quickly following administration of an appropriate dose of antivenom with correct species coverage. 
• There is no role for tranexamic acid in the treatment of venom induced coagulopathy. 
• There is usually no indication for blood product resuscitation. In cases of life-threatening haemorrhage where immediate reversal of coagulopathy is required, and an appropriate dose of antivenom has been administered use of FFP may be considered. FFP in this context has limited supporting evidence and may increase thrombotic complication risk. Appropriate antivenom is the treatment for venom induced coagulopathy. Discuss with an expert in all cases where reach-back is available.  

Hypotension and shock:

• Cytotoxic venom may cause widespread vasodilation and leakage of plasma into the interstitium. Large volume fluid resuscitation and blood pressure support may be required.
• In cases of haemotoxic envenoming with coagulopathy concealed haemorrhage should also be considered as a cause of shock. 
• Acute kidney injury
• Renal injury may be multifactorial and should be managed supportively. In severe cases renal replacement therapy may be required. 

Venom ophthalmia:

• Spitting of venom by cytotoxic elapids may cause intense pain with conjunctivitis and corneal erosions, which may be complicated by anterior uveitis and secondary infection if the eyes are not irrigated thoroughly and urgently. In severe cases endophthalmitis can occur.
• The mainstay of treatment is copious fluid irrigation followed by prophylactic topical antibiotics (eg chloramphenicol). 
• Irrigation should be followed by fluorescein staining and a detailed examination for corneal erosions, which if present should be assessed urgently by an ophthalmologist. 

Prolonged Casualty Care

When holding a casualty without access to laboratory diagnostics consider use of the 20-minute whole blood clotting test to assess for subclinical coagulopathy and to help prioritise patients for evacuation. 

Paediatric Considerations

Children are at increased risk of severe envenoming due to increased venom dose:body weight ratio.

Dose of antivenom in children is the same as in adults.