REM: Snake Bite / Envenomation

Snake bites are a potential medical emergency even though the majority do not involve significant envenomation. The role of the clinician in these circumstances is working out which patients have been envenomated, and the select group of patient which require anti-venom.

Appropriate and timely action of first aid principles are fundamental in reducing the morbidity and mortality associated with snake bites.

This is part of the Rural Emergency Module series (designed in particular for ACRRM Trainees).

Initial Assessment and Management

Recognise

Recognise, send for help, gather resources and appropriate equipment.
Move to appropriate area monitoring area.
Monitoring - HR, BP, RR, SpO2, Telemetry/Cardiac Monitoring (if available)
Identify snake if possible & avoid further envenomation by the assailant snake.
Apply immediate first aid principles and Pressure Immobilisation Bandage (see below) and keep the patient immobilised/still.
Ensure anti-venom available.
Liaise with a toxicologist as indicated.

Airway:

Assess for patency and protection
Intubate if respiratory failure or distress

Breathing:

Assess depth of breathing and respiratory rate, SpO2 + ETCO2 monitoring
Correct Hypoxia - SpO2 >93% in patients with no underlying lung condition

Circulation:

Establish IVC Access: Place in at least 1 IVC on non-affected limb for bloods.
2nd IVC should be established if unstable or likely to give Anti-venom.
Assess for bleeding from potential bite site, mucous membranes and IVC sites
Commence with IV fluid. Be mindful of fluid overload. Consider appropriate IV Fluid therapy in Rhadomyolysis and acute renal failure.

Disability:

GCS / AVPU
BSL
Assess for signs of flaccid paralysis, cranial nerve deficits, ptosis

Exposure:

Check temperature, maintain normothermia
Urine dipstick - check for haematuria and can be used for Snake Venom Detection as well.
Assess for myolysis: muscle pain, tenderness or weakness

Pressure Immbolisation Bandage

Wikihow: Pressure Immobilisation Bandage

History

Signs/symptoms

Evidence of a bite
Abnormal Bleeding
Evidence of descending symmetrical flaccid paralysis
Lymphadenopathy
Collapse / loss of consciousness
Nausea, vomiting, diaphoresis
Headache, ptosis
Abdominal pain, diarrhoea
Myalgias

Allergies
Meds

Anticoagulants, anti-platelets

PMHx:

Previous envenomation and/or exposure to antivenom
Asthma
Auto-immune disorders
Renal or Cardiovascular disease

Last oral intake
Events

Time and circumstances of snake bite
Was the snake seen, and any identifying factors of the snake (typically low-yield) - more useful if pet or snake handler
Number of strikes
First aid and PIB applied.

Investigations

PoC Bloods typically unreliable and not recommended
INR, APPT, fibrinogen, D-dimer,
FBC, U&Es, Ck
Snake Venom Detection Kit (can be used in conjunction with clinical + geographical information)
Urine dipstick

Management

Snake Antivenom

Snake anti-venom is the key treatment to managing significant evenomation and it's associated complications.

Indications: evidence of significant systemic evenomation (clinical or laboratory)

neurotoxic paralysis
coagulopathy
myotoxicity
acute renal impairment / failure
collapse and/or seizures

Contraindications

Nil absolute
Increased risk of anaphylaxis in those previously treated with anti-venom

Timing:

Efficacy is improved with early administration, once envenomation has been identified.
Risks of administrating anti-venom >24hrs post initial bite, may be greater than the risks of envenomation. Seek expert advice.

Choice:

Monovalent anti-venom is the preferred choice.
One vial of antivenom is now recommended to treat children and adults for all snake types.
The Australian Polyvalent snake venom will cover the 5 most common snake venom immunotypes in Australia and PNG. Increased risk of hypersensitivity reactions.

Administration:

All patient should recieve at least 1 dose of anti-venom if indicated. Further doses may be required dependent on snake, and assessed level of envenomation. Please see Clinician's Guide to Bite and Stings for more details.
Be prepared to treat anaphylaxis
Administer 1 ampoule diluted in 500ml of 0.9% saline IV over 20 minutes. In children aim to keep total volume less than 10 mL/kg.
Antivenom maybe given as a rapid IV push if the patient is unstable or in cardiac arrest

Adverse drug reactions:

Anaphylaxis
Serum Sickness

Supportive Cares

Fluid therapy and feeding: A Crystalloid is appropriate for the majority of patients. In potential life-threatening bleeds the use of FFP is reasonable. Limit oral intake initially to minimize risk of venom-induced vomiting causing aspiration pneumonia.
Analgesia, Antiemetic: Most patients with snake bite will not have significant pain. Simple analgesia should be sufficient. If pain is increasing it may indicate myolysis which requires reassessment. Narcotics should be avoided to minimize respiratory depression.
Anti-emetics can be useful in avoiding emesis and potential aspiration pneumonia, and also for patient comfort.
Antibiotics: Antibiotics are not routinely required as secondary infection from Australian snakes is uncommon. Tetanus immunity should be updated, once coagulopathy has been resolved.
Sedation: typically wish to avoid sedating the patient. This includes the use of sedating anti-histamines. Sedation only for intubation purposes.
Thromboprophylaxis: not required.
Head up position: nil particular position is mandated.
Ulcer prophylaxis: not routinely required.
Glucose control: maintain normoglycaemia 5-12 mmol.
Skin/eye care and suctioning: routine cares, monitor for signs of bleeding
Indwelling catheter: typically not required, but can be useful for monitoring urine output.
Nasogastric tube: typically not required, and mostly should be avoided.
Bowel cares: routine.
Environment: Maintain normothermia. Keep patient or transfer patient to a monitored environment, with access to onsite pathology.
De-escalation (e.g. end of life issues, treatments no longer needed)
Psychosocial support (for patient, family and staff)