Snake bite calls have been increasing at the Missouri Poison Center signaling the start of snake season as the warmer weather brings snakes (and people!) out of their nests. Most snakes found in Missouri are harmless and beneficial in the ecosystem, but we have five venomous species. We have already seen unnecessary and potentially harmful interventions used in the management of snake bites in hospitals across Missouri. Before you manage your next snake bite, review our recommendations for optimum treatment of a snake bite.
There are five venomous Crotaline pit vipers indigenous to Missouri.
- Copperhead (The vast majority of Missouri venomous bites, and often self-limited.)
- Water moccasin aka Cottonmouth
- Rattlesnakes (Timber, Pygmy, and Massasauga)
IS IT VENOMOUS?
Identification of the venomous snake, especially by killing it first, is not necessary because management is the same for all native venomous snakes. It can be helpful to know the distinguishing characteristics of venomous and nonvenomous snakes.
Cottonmouth – photo courtesy of the Missouri Department of Conservation
|Fangs that fold to the roof of the mouth|
|Heat-sensing pits below the eyes|
|May have a rattle|
|Bite has one or more fang marks/punctures|
|Management: See below|
Eastern Hog-nosed Snake – photo courtesy of the Missouri Department of Conservation
|Smooth, rounded head|
|Upper and lower row of tiny teeth; no fangs|
|Bite has 2 rows of small abrasions – similar to a tiny human bite|
|Management: Good wound care, up-to-date tetanus immunization|
THESE THERAPIES CAN LEAD TO WORSE OUTCOMES IN A VENOMOUS SNAKE BITE
Some therapies actually increase the risk for tissue damage and poor outcomes, although they may seem reasonable.
- Do not apply ice, a tourniquet or a constricting band; do not wrap the affected limb in anything tight fitting; and do not use pressure immobilization. These interventions increase the severity of tissue damage by preventing the dispersal of the cytotoxic venom and concentrating it locally.
- Do not cut, suction, explore, or excise the bite area.
- Do not apply electric shock therapy to the wound.
- Do not give prophylactic antibiotics (infection is rare) or steroids (unless true allergic reaction).
- Do not perform a fasciotomy. It is very rarely indicated and can be avoided with proper management and adequate administration of antivenom.
STEPS TO PROPER MANAGEMENT OF A VENOMOUS SNAKE BITE
Copperheads cause the mildest envenomation of all pit vipers, although significant local tissue is possible. Rattlesnake bites are more serious than either cottonmouth or copperhead bites with both severe tissue injury and systemic involvement including coagulopathy.
For any venomous snake bite: anticipate swelling, immobilize the limb and elevate it slightly above the heart. Mark and measure progression of swelling every 15-30 minutes.
1 Determine the Severity on Presentation
- History, location of bite, pre-hospital treatments
- Mark progression of edema
2 Strict Immobilization
- Elevate slightly above heart
- Limb activity enhances venom spread
- Nothing tight fitting; remove rings, watches, clothing with elastic bands
3 Baseline Labs
- CBC, PT/PTT, INR, fibrinogen
- Electrolytes, BUN, SCr, pulse ox.
Repeat in 4-6 hours
- if WNL twice, no need to re-check
4 Anxiety & Pain Control
- Anxiety: Benzodiazepines, calming environment
- Pain: Parenteral opiates; NSAIDs only if low risk of bleeding
- Tetanus booster as needed
- IV Fluids
- Monitor pulses in affected limb, use Doppler if necessary
- Not necessary in many envenomed bites
- Indication based on clinical severity
- See below
ANTIVENOM – WHEN TO GIVE, WHEN NOT TO GIVE
Antivenom is not necessary for all envenomated snake bites. CroFab® should not be given routinely on presentation, but should be reserved for those developing significant coagulopathy, systemic symptoms (CNS, GI, cardiovascular, or pulmonary), or extensive or rapidly progressing local tissue injury in the first 6-12 hours. Most envenomated bites in Missouri are copperhead bites, which are often self-limited, stabilizing and resolving with strict elevation and pain control.
Anavip® is another antivenom approved for North American rattlesnake envenomation that has resulted in significant local injury, coagulopathy, or systemic symptoms (CNS, GI, cardiovascular, or pulmonary). Anavip® offers no advantage over CroFab® for copperhead bites. Because the Anavip antibody fraction is a doublet, whereas CroFab® is single (see figure below), the half-life of Anavip® is longer. This reduces the incidence of recurrent coagulopathy in rattlesnake bites. Because copperhead bites do not produce coagulopathy in the first place, there is no advantage.
Antivenom does not reverse tissue damage that has already occurred; instead it halts or slows its progression in a severe envenomation. Fab antibody fragments work by binding and neutralizing venom toxins, facilitating redistribution away from target tissues and elimination from the body.
Contact Missouri Poison Center to receive our full snake bite management, including detailed indications and dosing for Crofab® and Anivip®.
If you have any questions about the management of snake bites, please feel free to call the Missouri Poison Center at 1-800-222-1222. Our specially trained nurses, pharmacists, and toxicologist can provide the most up-to-date information regarding exposures and treatment.