Assessing, Treating and Preventing Snake Envenomation

Learning Objectives

• Ensure your own safety when treating victims of snakebites.
• Identify the types of venomous snakes found in the U.S.
• Understand the effects of snake envenomation.
• Learn the special considerations to take when treating patients with snakebites.

KEY Terms

• Antivenin: A suspension of venom-neutralizing antibodies prepared from the serum of immunized horses or sheep.
• Compartment syndrome: Obstruction of extremity blood flow following an injury to a closed muscular compartment.
• Hemotoxic: Attacking both the tissue and the blood.
• Neurotoxic: Damaging or destroying nerve tissue.
• Rhabdomylosis: The breakdown of muscle fibers that leads to the release of muscle fiber contents into the bloodstream or myoglobin.

The Southern Pacific rattlesnake is a venomous pit viper found in Southern California and Baja California, Mexico. Photo Judy Torres

Although the majority of snakebites in the United States occur in the southwestern part of the country,¹ at least one type of venomous snake can be found in every state except Alaska and Hawaii. Medics working in areas where venomous snakes are uncommon may not be as familiar with treatment as they’d like, knowing they may not come across a snakebite victim in their entire career. Nonetheless, if by chance one of your patients does get bitten, knowing what to do could be the difference between life and death.

Pathophysiology & Statistics
The World Health Organization estimates that snakebites kill between 20,000 and 94,000 people worldwide each year.² In the United States, approximately 8,000 people are bitten by poisonous snakes each year, but only about 9—15 of these victims die.³ Snakebite envenomation has been traditionally treated with the administration of animal-derived antivenins that successfully reduce the impact of the poison and lower morbidity. However, antivenins treatment doesn’t necessarily reduce local tissue damage that leads to permanent disability. Studies show that most bites involve limbs/extremities, and snakebites cause up to 400,000 amputations worldwide each year.² This is usually due to necrosis and distant muscle involvement called rhabdomyloysis, which can lead to kidney damage. In the case of a venomous snakebite, the goal is to save a life and prevent a lifelong disability.

We also need to remember that snakes are kept as pets in many households in the U.S.

In fact, there are 7.3 million pet reptiles in the U.S., with snakes being the most common.⁴ People in many communities across the country keep venomous snakes as exotic pets. Knowledge and review of what to do in case of a snakebite can become essential to these pet owners.

The Trans-Pecos copperhead is a venomous pit viper found in western Texas and northeastern Mexico. Photo Judy Torres

Two types of venomous snakes are found in the U.S. Snakes from the family Crotalinae, or pit vipers, represent 99% of all the venomous snakebites in the U.S. These include rattlesnakes, copperheads, cottonmouths and water moccasins. The majority of victims are bitten on an extremity and are men, and most bites occur in the warmer months, when people enter the snake’s natural environment, or during attempts to handle the snake. Bites from crotalid snakes are typically hemotoxic and usually appear as two fang punctures with local swelling and necrosis.⁵

North American elapid snakes (from the family Elapidae), such as the coral snake, have a neurotoxic venom designed to paralyze and kill prey. The venom usually causes local numbness instead of pain and swelling, with the risk of cranial nerve palsies, respiratory paralysis and death.⁵

Snakebite Prevention
Scene safety is crucial for you and of the utmost importance for the victim. It’s important to be aware of your surroundings in case the snake (or another snake) is nearby.

Coral snakes emit a potentially deadly neurotoxin and are noted for their red, yellow, white and black bands. CanStockPhoto/zebraman777

First and foremost, remember to stay calm. Don’t panic when you realize you’re near a snake. Don’t disturb the snake; most snakes don’t act aggressively without being provoked. Under most circumstances they’re more afraid of us than we are of them. Avoid and get away from the snake if possible. If treating a bite victim or if bitten yourself, remember that any movement or exertion may increase the spread of the venom throughout the body. Don’t try and capture or kill a live snake and remember that even a dead snake can cause an envenomation.

Depending on the size of the snake, striking distance can be from 3—6 feet or about half their length. It’s helpful to be aware of the types of venomous snakes common to your area and their habitats.

Pit vipers have a triangular-shaped head and elliptical pupil, deliver dry bites (no venom injected) up to 25% of the time, and are responsible for most venomous snakebites in the U.S. Their bites result in almost immediate swelling, darkening of tissue, a tingling sensation and nausea.⁶ Pit vipers can be found throughout the country:

• Rattlesnakes generally prefer grasslands and rocky hillsides. (They may not make any noises/rattles!)
• Timber rattlesnakes in the northern U.S. typically populate timbered hillsides with south-facing ledges and rock slides. In the southern U.S., these snakes are often found near swamp borders, pine woods and cane thickets.
• Cottonmouths live near swamps and rivers.
• Copperheads are found in aquatic or dry areas, rocky wooded hillsides, swamp edges and pine woods near canyon springs.

Coral snakes are noted for their red, yellow, white and black bands. Compared to pit vipers, coral snakes are relatively small in size, averaging about 3 feet in length.⁷ Approximately 50% of all coral snake bites are dry, where no venom is injected. Coral snakes are generally found near pine woods, lake edges and sandy open woods.

Cottonmouth bite to the thumb after removal of damaged tissue. Photo courtesy Saralyn R. Williams, MD

Snakebite Treatment
Keep the patient calm and reassured. Have them lie down and remain still and try to restrict overall movement. Monitor airway, breathing, circulation, disability (of nervous system), exposure/environmental control (protect from cold/water) and begin treatment immediately.

Take the patient’s vital signs initially and repeatedly–at least every five minutes. Conserve the victim’s body heat. Also make note as to what first aid has already been attempted or delivered prior to EMS arrival. Protect the injured area and keep it clean and dry, even gently immobilizing the limb to prevent movement and pain. All jewelry or anything on the bitten limb should be removed as soon as possible.

Cottonmouth bit to thumb showing bullae up the arm. Photo courtesy Saralyn R. Williams, MD

Follow the uniform steps for patient assessment, noting the following:

• Signs and symptoms: Is the patient experiencing any pain, numbness, paresthesia, dyspnea, nausea, vomiting, dizziness, edema, erythema, syncope, dyspnea, difficulty swallowing, confusion, hypotension, hemoptysis, epistaxis, tachycardia, diarrhea, seizures or elevated temperature?
• Allergies: Treat allergic reactions to snakebites per local protocol.
• Medications: Does the patient use prescription blood thinners or anticoagulants?
• Past history: Does the patient have a history of previous snakebites or antivenin therapy given?

Copperhead bite to long finger. Photo courtesy Saralyn R. Williams, MD

Always remember: Snakebite victims need immediate and definitive medical care. Rapid transport to the closest ED or other appropriate facility is critical. During transport, treat the patient with at least one 18-gauge IV on the unaffected arm, provide oxygen, monitor vital signs/ECG and administer pain medications if necessary. When calling the hospital, ask the staff to contact a poison control center immediately and locate the nearest antivenin resource and physician consultants. Describe the snake and bite wound, if possible, so the appropriate and proper amount of antivenin can be administered. (See Snakebite Grading Scale, below.)

Be on the lookout for signs of shock, changes in mental status, limb vascular and neurological status, and anaphylaxis. Treat these according to local protocol.

Patients with extremity bites are at risk of, although rarely compromised by, infection and compartment syndrome. Symptoms of compartment syndrome, a surgical emergency, include disproportionately severe pain, weakness of intra-compartmental muscles, pain on passive stretching of intra-compartmental muscles, hypesthesia of areas of skin supplied by nerves running through the compartment, paralysis, pallor, and obvious tenseness of the compartment on palpation.⁸

Providers should note any signs and symptoms of kidney injury, including low urine output, nausea and vomiting, hiccups, fever, drowsiness, confusion or altered mental status, coma, tremors, twitching, seizures, pericardial friction rub, and signs of fluid overload.⁸

Crotalid snakebite of foot with comparison to unaffected leg. Photo courtesy Saralyn R. Williams, MD

Special Considerations
In remote areas where definitive care is over 30 minutes away, you should take additional steps to prevent the spread of venom. Cover the site with a sterile pad or several 4 x 4s, then immobilize the affected limb with a splint.

If the victim has symptoms of neurotoxic envenomation (from a coral snake or other elapid) you should use the pressure immobilization method, wrapping the affected limb with a wide and firm elasticated pressure bandage, starting from the extremity and working the wrap up the length of the arm or leg; keep the limb below heart level and marking the location of the bite. Be careful not to cut off circulation. Don’t remove pants or shirts since this may cause the venom to enter the bloodstream. Check the patient’s pulse, sensation and temperature every five minutes and watch for restricted circulation as the limb may continue to swell. The purpose is to prevent the spread of venom by the lymphatic system, not the flow of blood.

Any preexisting conditions should be noted and can be extremely important, especially when relaying information to the ED or other receiving facility. This is especially important for elderly patients, where the higher incidence of pre-existing conditions combined with associated frailty place them at higher risk should envenomation occur.⁹

Pediatric patients’ risk factors are similar in nature to adults except that a child has a smaller body mass, so any snake envenomation may cause a proportionately more severe response.⁹

Other considerations to take when treating snakebite patients are:

• Never use ice or a tourniquet;
• Don’t cut or suck the wound;
• Never use any type of electric shock; and
• Try to determine the type of snake or its description through visual clues while on scene or patient or eyewitness accounts.

Antivenin for Snakebites
Upon delivery to the ED or other appropriate facility, antivenin specific to the type of snake responsible for the bite is given to neutralize the effects of the venom. Venom may be a combination of many toxins, including cytotoxins, hemotoxins, neurotoxins and myotoxins.

Current treatment involves monoclonal antibody therapy for crotalid bites. Crofab (crotalidae polyvalent immune fab [ovine]) is the current drug of choice for envenomation of grade 1 and higher bites.

Vials of antivenin are given by IV and the clinical course is followed to determine duration of therapy.

Patients are stabilized and laboratory abnormalities are corrected, especially if the envenomation has resulted in anticoagulation abnormalities.

Antivenin is expensive and is sometimes in short supply. Recommendations are that it should be used only in patients where the benefits of treatment outweigh the risks of antivenin reactions (anaphylaxis or serum sickness). Indications for the use of antivenin are signs and symptoms of systemic and or severe local envenomation.

Conclusion
Experts feel medical personnel “would benefit from more formal instruction on all aspects of the subject.”⁸ Furthermore, any medical professional (doctors and EMS providers alike) needs guidelines when treating a snakebite victim. These guidelines should be developed, reviewed and practiced as with other treatments such as with ACLS and ALS/BLS protocols.

References
1. Russell FE. Snake venom poisoning. Scholium International: Great Neck, N.Y., p. 163, 1983.
2. McNeil DG, Jr. (Dec. 11, 2011.) Public health experts calls for a new emphasis on snakebites. New York Times. Retrieved March 28, 2014, from www.nytimes.com/2011/12/13/health/public-health-experts-calls-for-a-new-emphasis-on-snakebite.html.
3. North Carolina State University Cooperative Extension. (n.d.) Snake bite first aid. Retrieved March 28, 2014, from www.ces.ncsu.edu/gaston/Pests/reptiles/snakebitetx.htm.
4. James S. (May 18, 1996.) Creature feature slithers in. Sun-Sentinal. Retrieved March 28, 2014, from http://articles.sun-sentinel.com/1996-05-18/news/9605170621_1_reptile-snakes-amphibian.
5. Juckett G, Hancox JG. Venomous snakebites in the United States: Management review and update. Am Fam Physician. 2002;65(7):1367—1375.
6. Howard WE. (1994.) Control of rattlesnakes. Internet Center for Wildlife Damage Management. Retrieved March 28, 2014, from www.icwdm.org/handbook/reptiles/RattleSnakes.asp.
7. Behler JL: National Audubon Society first field guide: Reptiles. Scholastic: New York, 1999.
8. Warrell DA. Guidelines for the management of snake-bites. World Health Organization Regional Office for South-East Asia: New Delhi, India, 2010.
9. White J. (2002.) Notechis scutatus. Women’s and Children’s Hospital Toxinology Department. Retrieved March 28, 2014, from www.toxinology.com/register/tigersnake_example.pdf.

More Trauma Care from JEMS.com