Snakebites – and Envenomation

shutterstock_93999454I credit the information that I’ve learned and written here to Richard Clark, MD who is medical toxicologist and expert in Wilderness Medicine.

 Snakebites are fairly common, but rarely cause death.  There are 350,000 snakebites each year in the world with 35,000 deaths annually worldwide and only 10-15 deaths per year in the US.

In the U.S. there are 3 main types of snakes:  Colubrids, Elapids, and Crotalids.  Most snakes in the U.S. are nonpoisonous and have fixed hind fangs.  The Garter snake is a common example of this kind of snake (a Colubrid).  The Colubrids have round pupils.

The Elapidae are snakes that have front fixed fangs with modified grooved teeth such as Cobras and Mambas and Coral Snakes. They require a longer bite time to envenomate than the Crotalids.

Coral snake venom is neurotoxic and causes parasthesias, weakness, paralysis and cardiovascular collapse.  The treatment is supportive care and prophylactic antivenom.

Crotalidae are the pit vipers that have mobile front fangs that are a very efficient envenomation apparatus.  In the U.S. the Crotalidae are the Rattlesnakes, the Cottonmouth and Copperhead.  They have a triangular shaped head and heat sensing organs around their nose.  They have elliptical pupils and don’t always rattle before striking.

Death is actually rare from Rattlesnake bites although tissue damage is common and can be severe.  The pit viper venom can cause tissue damage, coagulopathy, thrombocytopenia, neurotoxicity, shock and pulmonary edema.  The area of the bite usually has swelling, blebs, and sometimes necrosis.  The incidence of wound infection after being bit by a Rattlesnake is very low because the venom actually prevents bacterial infections.  If bitten by a Rattlesnake and there is no swelling/pain, there is no envenomation.  This is called a dry bite and happens in up to 25% of these bites.

There has been some controversy over whether to use ice, incision, constrictive bands, or perform excisions or fasciotomy.  We generally don’t recommend any of these treatments any longer and have found that they are not effective and may cause more harm.

Rattlesnake first aid:

1)   Seek medical care

2)   No suction

3)   No ligatures

4)   No cutting

5)   No ice

6)   The Anti-Venom is called Crofab.  We generally give anti-venom until the proximal swelling halts, and coagulopathy is resolving, the thrombocytopenia is resolving and the systemic toxicity is resolving.  This may involve many doses of anti-venom.  The initial dose is 4-6 vials in 100 mL of NS.  Begin slowly and infuse over 1 hour.  Redoes with 4-6 vials as needed for “stabilization.”  One problem with the anti-venom is that some people are allergic.  The majority of allergic symptoms are rash.  It is also very expensive and not readily available.

7)   If the bite is on the face, empiric intubation should be done to protect the airway because facial bites can lead to significant swelling.

If you are interested in learning more about wilderness medicine, a great resource for information is the wilderness medicine society:  http://www.wms.org/

This document is for informational purposes only, and should not be considered medical advice for any individual patient.  If you have questions please contact your medical provider.

 

I hope that you have found this information useful.  Wishing you the best of health,

Scott Rennie, DO

Blog: https://doctorrennie.wordpress.com

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