Many people still remember the old western films where the lead actor would be bit by a snake and his trusty side-kick would cut between the teeth marks and suck out the venom. We have come a long way in our understanding of snake bite management, but there are still many misconceptions out there that need to be put to rest. So let’s say you are out on a run with your dog and yo
u are walking up to your car to head back home for a shower when you feel a sting on your ankle and hear that characteristic sound of a rattle (story of a real patient we treated in the summer of 2015 in Texas). What now?
First off, if you are with the person who has been bitten, reassure them they will be okay. If you have been bitten, reassure yourself. Up to 25% of snakebites are actually ‘dry bites’, in which no venom has actually been injected, and severe envenomations occur in only about 12% of bites. Take off all jewelry from extremity bitten as well as any restrictive clothing or shoes of it the bite occurred in the distal lower extremity. The most important step following this is transportation to the nearest medical facility. Immobilization of the limb using a splint may be applied quickly, and the person who was bit should try to remain as immobile as possible to reduce muscle contractions and prevent high rates of blood circulation which will spread the venom faster throughout the body. Also, limb elevation is essential for pit viper envenomations (e.g. rattlesnakes, cottonmouths and copperheads). Raising the limb as high as possible reduces the hydrostatic pressure within the limb, minimizing tissue damage. If the bite occurs outdoors, and is not due to a domestic snake that is not native to the area, identification of the exact snake is less important (within the continental US). This is because the antivenom used to treat endemic North American envenomations covers rattlesnakes, cottonmouths and copperheads. If you can get a look at the snake and remember general characteristics (i.e. colors, head shape (triangular vs. elliptical), and body shape) this may be helpful in determining if the snake was venomous, however increasing swelling and erythema around the wound are signs of envenomation and more reliable than snake descriptions most of the time.
There are three species of coral snakes in North America, and they become much more potent as you travel from west to east across the country. In the case of an envenomation of a neurotoxic elapid (e.g. coral snakes), pressure immobilization may be of benefit (only supported by an Australian trial involving restrained monkeys). In this case, wrap the entire extremity in an Ace-Bandage tightly, but not enough to cut off the peripheral pulse, and fix it in an immobile position using a splint or sling. However, elapid bites account for <1% of snake bites in North America and because pressure immobilization is harmful and in no way beneficial for pit viper envenomation it should not be performed in the case of a North American snake bite. There is currently a relative shortage of coral snake antivenom as Pfizer/Wyeth has been the sole producer in the United States and discontinued production. When the present stocks are gone, there will no longer be an FDA-approved antivenom for coral snake bites.
Now to dispel some myths.
- Do not apply a tourniquet – tight tourniquets have actually been responsible for increased morbidity and mortality in snake bite victims. They can cause increased ischemia and gangrene of the limbs in prolonged use (>2hrs) and can cause nerve damage, increase the local effect of the venom and cause rapid development of systemic envenomation after their release.
- Do not cut or puncture the area of the bite – this only increases the possibility of the bite site becoming infected and does not help to remove the venom. If envenomation causes an anticoaguated state, this action can also lead to uncontrolled bleeding.
- Do not suck the bite site or use a vacuum pump – again this can lead to increased infection, and has never been shown to have any efficacy in removal of the snake venom. Even when extractors were applied to patients immediately after envenomations and filled multiple times, the fluid that was pulled from the puncture sites contained minuscule amounts, if any amount, of venom. In these studies, the extractors removed only about 0.04-2.0% of the envenomation load and did nothing to decrease the local erythema or swelling. Strong suction can even lead to localized tissue damage and necrosis.
- Do not apply chemical compounds, ice packs, “snake stones” or electric shocks to the area – none have shown any benefit
Early pain control can be important as the local pain can be intense. Oral acetaminophen or opioids are preferred as the use of NSAID’s or aspirin can increase the risk of bleeding in an anti-coagulated state. Anti-emetics may also be necessary as vomiting can be an early symptom of systemic envenomation.
It may be best to keep the patients in a seated position or to keep the bitten extremity below the level of the heart to try to slow the spread of the venom, but the effectiveness of this is debated. Significant third-spacing can occur due to increased vascular permeability and can contribute to hypotension along with vomiting, hemorrhage or vasovagal effects. Fluid administration should begin as quickly as possible with administration of crystalloids. Anaphylaxis should be treated with IM Epinephrine. In the case of respiratory distress due to the neurotoxic effects of an elapid envenomation, intubation or even mouth-to-mouth respiration’s en route to the nearest medical facility can be life-saving.
For the treatment algorithm for administering CroFab antivenom use the following link: http://www.crofab.com/documents/CroFab-Treatment_Algorithm.pdf.
In May of this year a new antivenom, Anavip, was approved by the FDA for treatment of pit viper bites, but it is not yet available in this country.
Big thanks to Dr. Greene of the Emergency Department at Baylor College of Medicine and well known toxicologist, for his review of this article.
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Bush, S. (2004). Snakebite Suction Devices Don’t Remove Venom: They Just Suck. Annals of Emergency Medicine, 43: 187-188.
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Warrell, D. (2010). Guidelines for the Management of Snake-Bites. World Health Organization, 625-625.