snake bites

BACKGROUND INFORMATION ON SNAKEBITES

• 3000 snake bites reported in Australia per year, antivenom required in 100-200 cases with 1-4 deaths (most deaths from Brown snakes)
• Brown snakes, Death Adders and Taipans (in that order) are the most common causes of significant envenomation in our area
• Venom spread via lymphatic flow
• 95% bites on extremities
• 25-50% result in systemic envenomation
• Early envenomation symptoms (<1 hour) are headache, nausea and vomiting
• Amateur and even some “local expert” identification of snakes is unreliable

Prehospital

First Aid:

• Keep the patient calm
• Avoid unproven techniques such as tourniquets or sucking the bite
• Apply a Pressure Bandage Immobilisation (PBI)

PBI Video

• Preferentially an elasticated bandage is preferred for a PBI at a pressure similar to a sprained ankle
• The use of a PBI 4 hours post bite is unlikely to be effective
• Immobilise the whole patient
• If the bite is on the torso, apply local pressure to the area and immobilise the patient
• Do not wash the wound as in a few cases a wound swab will be required for a CSL Snake Venom Detection Kit (SVDK)
• The PBI should not be removed until the patient has been fully assessed and found to show no objective evidence of envenomation or they have been envenomed and receiving antivenom (usually the PBI is removed once half of the antivenom has been infused)

Transport

The patient requires a hospital that has the following:

• A doctor that can manage snakebites and potential complications (e.g. anaphylaxis)
• 24 hours laboratory capability
• Adequate stocks of antivenom or capability of this being transported to the hospital in a timely fashion

If the above is not met, initial management may occur at the first site and then retrieval services will transfer out. If envenomation is clinically evident then antivenom maybe brought out by the retrieval services and started en-route to the next hospital.

Hospital

Resuscitation

• Most patients with a history of snakebite do not require immediate resuscitation but should be initially assessed in a an area capable of cardiorespiratory monitoring
• Establish IV access
• Early Life threats include:
  • Cardiac Arrest (most commonly seen with brown snake envenomation, although rare, 1 ampule of antivenom can be given undiluted as an IV push and resuscitation proceeds along conventional lines)
  • Sudden Collapse (hypotension)
  • Respiratory Failure secondary to paralysis
  • Seizures
  • Uncontrolled haemorrhage secondary to severe venom-induced consumptive coagulopathy (VICC)

Envenomed or not?

• The aim over the next 12 hours (post bite) is to determine if the patient has been envenomed and if so, which snake is responsible. This is based on the history, examination and investigations (never use bedside point-of-care INR and D-dimer as they are inaccurate).

Clinical features

• General
  • Severe headache
  • Nausea
  • Vomiting
  • Abdominal pain
  • Diaphoresis
  • Fang marks
  • Abdominal pain
  • Draining lymph nodes may be enlarged and painful
• Coagulopathy (consumptive-onset <1 hour)
  • Venom-induced consumption coagulopathy (VICC)
    • Usually present on presentation
    • INR is usually so high that the lab refuses to report the actual figure (i.e. the PT is infintely prolonged). In “incomplete” VICC,  the INR is over 3.0.
    • aPTT is prolonged – at least over 100
    • Fibrinogen is low
    • Quantitative D-dimer is usually extremely high
    • Associated with a thrombotic microangiopathy: thrombocytopenia, microangiopathic haemolytic anaemia and acute renal failure (platelet count should be below 100)
  • Anticoagulant coagulopathy (some black snakes)
• Neurotoxicity (onset 1-3 hours)
  • Evolves over hours
  • Progressive descending flaccid paralysis
    • Classically
      • eyes are the first to go (ptosis, diplopia and blurred vision)
      • Bulbar involvement follows
  • Respiratory muscle paralysis and limb paralysis are the end stage
• Myotoxicity (delayed onset)
  • Evolves over hours
  • CK is normal on admission, but rises in the first 48 hours
  • Rhabdomyolysis
  • myoglobinuria
  • secondary kidney impairment
• Thrombotic microangiopathy
  • Thrombocytopaenia, microangiopathic haemolytic anaemia and acute kidney impairment
• Kidney damage
  • Secondary to thrombotic microangiopathy or rhabdomyolysis
• Local cytotoxins
  • Local pain, swelling and bruising (eg. brown snake bites)
  • Tissue damage (uncommon in Australian snakes)

Snake Group	Coagulopathy	Neurotoxicity	Myotoxicity	Thrombotic microangiopathy
Brown	+++	+/-		+
Death Adder		+++
Taipan	+++	+++	+	+
Tiger	+++	++	++	+
Black	+		+++
Sea snake		++	++

Assessment

Focus on evidence of envenomation. 

• Once the possibility of snakebite has been raised, it is important to determine whether a child has been envenomed to establish the need for antivenom.
• This is usually done taking into consideration the combination of circumstances, symptoms, examination and laboratory test results.
• Most people bitten by snakes in Australia do not become significantly envenomed.

History and Examination

Circumstances	Symptoms	Examination
Confirmed or witnessed bite versus suspicion that bite might have occurred Were there multiple bites?When? Where? First aid? Past history? Medications? Allergies?	Headache Diaphoresis Nausea or vomiting Abdominal pain Diarrhoea Blurred or double vision Slurring of speech Muscle weakness Respiratory distress Bleeding from the bite site or elsewhere Passing dark or red urineLocal pain or swelling at bite site Muscle pain Pain in lymph nodes draining the bite area Loss of consciousness / collapse and/or convulsions	Evidence of a bite / multiple bites   Evidence of venom movement (eg swollen or tender draining lymph nodes) Neurotoxic paralysis (ptosis, ophthalmoplegia, diplopia, dysarthria, limb weakness, respiratory muscle weakness) Coagulopathy (bleeding gums, prolonged bleeding from venepuncture sites or other wounds, including the bite site) Muscle damage (muscle tenderness, pain on movement, weakness, dark or red urine indicating myoglobinuria)

On Arrival

• -Apply pressure immobilisation (PI) (bandage, splint and immobilize) if
• -less than 15 minutes post snake bite
• -severe envenomation present
• -Otherwise leave off or re-enforce existing bandage

Clinically Envenomated

• ABC’s
• Consider polyvalent anti-venom 1 ampoule or monovalent antivenom as per Clinical Effects Algorithm
• Urgent bite site swab with normal saline moistened black swab placed back into sheath or urine if no identifiable bite site (or site VDK negative)
• Initial bloods FBC / UE / CK / LDH / Coags & D-dimer/Group and Hold (point of care Coags testing IS NOT to be used)

NOT Clinically Envenomated

• Swab bite site with normal saline moistened black swab and place back into sheath.
• Place the fully labelled specimen and pathology form into a red specimen bag, leave at patient’s bedside, Do Not Send To Pathology
• FBC, UE, CK, LDH, Coags & D-dimer, BSL (point of care Coags testing IS NOT to be used).
• If initial bloods are normal, the only serial tests required are Coags & CK (serial test timings are from time of removal of pressure immobilisation).
• Observe in ED

Giving Antivenom

• Antivenom is indicated where there is evidence of envenomation.
• Giving antivenom should occur in consultation with a clinical toxicologist.
• Give one vial of tiger and one vial of brown snake antivenom without delay.
• Dilute one vial in 100mls of 0.9% saline and give IV over 15-30 min. 
• If in cardiac arrest and this is thought to be due to envenomation, then give undiluted antivenom via rapid IV push.
• There is no weight based calculation for antivenom (the snake delivers the same amount of venom regardless of the size of the child).
• One vial of antivenom is enough to neutralize the venom that can be delivered by one snake.
• Clinical recovery takes time after antivenom administration and multiple vials do not speed recovery.

Venom induced coagulopathy takes time to reverse.

• It takes 10 – 20 hours to start to improve and 24 – 30 hours for complete resolution.
• More antivenom than recommended will not aid recovery of clotting factors.
• The role of FFP or cryoprecipitate is controversial and should be discussed with a clinical toxicologist; generally it is indicated if the child is bleeding.

Other management considerations:

• Gain 2 points of intravenous access, with at least one large bore cannula.
• There is a risk of anaphylaxis with antivenom administration – be prepared to treat.
  • If anaphylaxis occurs, treat as per the anaphylaxis guideline and consult with a clinical toxicologist. 
  • Given the risk of intracerebral haemorrhage with coagulopathy and the possible elevation of blood pressure with adrenaline, a more easily titratable intravenous adrenaline infusion may be considered in discussion with an expert experienced in its use.

Role of snake venom detection kit (VDK) 

• used for Identification of Snake Venom:
• DKs are used to identify the type of snake venom in a patient who has been bitten. This is crucial for determining the appropriate antivenom.
• Attempted identification of snakes by witnesses should never be relied upon as snakes of different species may have the same colouring or banding
• Causes of False Positives and Negatives
  • Cross-Reactivity: VDKs may show false positives due to cross-reactivity with venoms from different snake species.
  • Environmental Contaminants: Contamination from the environment or previously used medical equipment can lead to false positive results.
  • Low Venom Concentration: A false negative may occur if the venom concentration is too low for detection by the kit.
  • Timing of the Test: The timing of the test relative to the bite can affect results. Too early or too late testing can lead to false negatives.
  • Improper Sample Collection or Handling: Errors in sample collection, storage, or handling can also lead to inaccurate results.
• Reasons Against VDK Use on Blood
  • Low Sensitivity in Blood: VDKs are typically less sensitive when used on blood samples. Venom components may be rapidly distributed, metabolized, or bound in the bloodstream, making detection difficult.
  • Interference with Blood Components: Blood components may interfere with the assay, leading to unreliable results.
  • Preferential Binding to Tissues: Some snake venoms bind preferentially to tissues rather than staying in the bloodstream, reducing the chances of detection in blood samples.
  • Risk of Hemolysis: The process of blood collection and handling may lead to hemolysis, which can interfere with the test results.
  • Clinical Focus on Symptomatology: The management of snakebites primarily relies on clinical symptoms and signs rather than solely on venom detection. Thus, testing blood may not significantly change clinical management.
• If used:
  • VDK testing can be done on bite sites and urine
  • Leave the pressure immobilization bandage in place – to obtain the bite site swab, cut a hole in the bandage
  • single operator should be dedicated to perform the VDK interpretation and should do so free from other clinical responsibility and interruption.
  • This takes 20-30 minutes, and as such should be omitted in the unwell or arrested
  • A brief lapse in concentration when watching for colour change in the VDK can result in a false reading
  • If there is no apparent bite, a VDK may be done on urine, but never blood

Adrenaline Infusion for Anaphylaxis

• Allergic or anaphylactic reactions to antivenom occur in 25% of cases (5% are severe)
• Not required as a routine premedication, but must be rapidly available
• Higher risk groups may include: previous antivenom use, previous antivenom reactions, history of allergy to animal proteins (particularly horse), snake handlers (always consider anaphylaxis to the actual venom in snake handlers)
• Cease antivenom, call for help, give O2, lie flat, Normal Saline fluid bolus if hypotensive (20 mL/kg)
• IM Adrenaline in lateral thigh 0.01 mg/kg (up to 0.5 mg) if immediate response required, otherwise IV as below
• 1 mg Adrenaline in 100 mL Normal Saline via infusion pump, start at 0.5-1 mL/kg/hr and titrate
• Cautiously restart antivenom once reaction controlled

Discharge Criteria

• Normal bloods at ≥ 6 hours post removal of PI (or at 6 hours post snake bite if reliable history, otherwise 6 hours post presentation)
• No signs of envenomation (coagulopathy, paralysis, myolysis, renal failure)
• Review patient’s tetanus status
• No discharges overnight
• Safe environment to discharge patient home into
• Discharge advice provided (written & verbal)
• Consider longer period of observation (up to 24 hours) for suspected
  • Death Adder bites (Magnetic Island, rural environment, or description of short squat snake with characteristic tail) – delayed onset paralysis.
  • consider up to 24 hours observation (and repeat bloods at 12 hours) for suspected Mulga, Collett’s and bites in snake handlers (often exotic or geographically relocated snakes).
• Patient asymptomatic