I live in a country that boasts 19 of the worlds top 23 most venomous snakes. Deadly slithering hypoderms waiting to sneak up an unguarded trouser leg and inject you with a coctail of neurotoxins, haemolytic and haemorrhagic enzymes, pro and anti coagulants, myotoxic, cytotoxic and nephrotoxic factors, all guaranteed to ruin your day. The Fierce Snake (Oxyuranus microlepidotus) produces the most toxic venom of any land based snake in the world, being around 1,000 times more toxic than the American Rattler. One dose of its venom is powerful enough to kill around 500,000 mice. Luckily, it is a very shy snake and only lives in remote desert regions. The Eastern Brown Snake (Pseudonaja Textillis), on the other hand, lives all along the east coast of Australia. In fact there are bound to be a few within spitting distance of where I sit this very moment. It is the second most venomous land snake in the world and one of the most dangerous. It can be aggressive, fast moving and has been known to follow people home at night, knock on their doors, leap up and then repeatedly attack.
first aid treatment.
- As soon as possible identify the area bitten.
- Immobilize the victim.
- Cut clothing around the bite site rather than removing it, as increased activity only forces more venom into the bloodstream. If possible mark around the bite site with a pen.
- Do NOT wash or clean the site. Venom is not absorbed through the skin and any residue may be useful in venom identification.
- Apply a broad pressure bandage. You need to bandage upwards from the lower portion of the bitten limb. Include fingers or toes in the bandage. Make it as firm as you would for a sprained ankle and extend it the entire length of the affected limb. Immobilize the limb (use a splint if possible) and then immobilize the patient. (Bring transport to the patient rather than trying to get them to transport.) Bandages should NOT be removed or loosened until the patient has reached hospital and resuscitation and monitoring equipment is available.
- Do NOT apply a tourniquet.
- And do NOT attempt to capture or kill the snake and bring it into the ED and drop it in the face of the Triage nurse. You only increase the risk of getting yourself envenomated by the snake or beaten by the nurse. Probably both.
name your poison.
Once in the ED the patient should be assessed for any immediate threats to their ABC’s. Even though the patient may have been bitten multiple times and have clear bite marks they may not have been envenomated. This will depend on several factors:
- Fang length. Immature snakes may have short fangs that are unable to penetrate through clothing. Fangs may also have been broken or damaged (snakes don’t floss much).
- Time of last venom injection. If the snake has recently injected venom whilst obtaining its lunch its venom sacks may not have yet replenished a significant yield.
- Decision to inject. Snakes make a conscious decision to inject their venom and may make a “dry bite”.
Antivenom is only administered if the patient develops definite systemic symptoms of envenomation. Some indicators may include:
- Neurological: ptosis, pupillary impairment, motor impairment, decreased GCS, pain, numbness, paraesthesia.
- Cardiovascular: bradycardia or tachycardia, hypotension or hypertension.
- Respiratory: bronchospasm’ pulmonary oedema, respirtory muscle impairment.
- Gastrointesinal: nausea and vomiting, haematemesis.
- Integumentary: bleeding at bite site, IV site, gingiva and diaphoresis.
- Musculoskeletal: myalgia.
- Urinary: haematuria, myoglobinuria, oliguria, anuria.
The Australian Venom Research Unit (AVRU) has a great step by step guide in assesssing symptoms of snakebite envenomation. Correct identification of a snake is a tricky business and even experienced herpetologists (no, nothing to do with herpes) get it wrong. Giving the wrong antivenom is dangerous and can lead to unnecessary death of the patient. Luckily, we are the only country in the world with Snake Venom Detection Kits (SVDKs) which allow the most appropriate and effective antivenom to be given. Instructions on use of our SVDK can be found at the AVRU website. Using one, is kinda like playing with a kids chemistry set, so its useful to familiarize yourself with it so as not to blow yourself up.
Snake antivenom is produced from the serum of horses that have been immunised with sub-clinical doses of specific snake venom. When enough antibodies are detected in the serum it is collected and fractionated and purified into antivenom. Because these antivenom remain essentially a horse protein, they may result in adverse reactions such as anaphylaxis and serum sickness and strong urges to eat hay. Once the snake venom has been identified a corresponding monovalent antivenom is administered IV. A single dose of antivenom is based on the average venom yield of the snake, but because snakes often deliver much higher doses, a patient may require multiple doses of antivenom to neutralize the venom (a case in 2001 required 28 vials of antivenom to neutralize a Brown Snake bite). Before administering antivenom, advanced life support, and experienced staff must be present.