Summer Medicine: Evaluation & Treatment of Snakebites

Hailing from the Pacific Northwest, where snakes are common, but not a health hazard, I rarely think about the possibility of snakebite emergencies. Now, living in Tennessee, things are different. There are a number of venomous snakes indigenous to the United States. Summertime, when outdoor activities, like wading in creeks and working in fields is common, snakes do pose a potentially serious danger. The other day while I was working in the emergency department, a patient arrived with the first serious snakebite we have seen this summer, prompting me to brush up on my envenomation know-how. 

If you're a nurse practitioner practicing in an area where patients have the potential to present with bites from venomous snakes, it is essential that you are prepared to address these in your practice. If you live in an area where venomous snake incidents are less likely, (after considering yourself lucky!) familiarize yourself with envenomation treatment protocols on the off chance that a patient gets a little too cozy with a serpentine pet. Check out the following overview of the evaluation and treatment of snakebites. 

Venomous Snakes in the United States

Most snakebites are a result of nonpoisonous snakes, however, each year in the United States, about 8,000 venomous snakebites occur. The most common culprit is the rattlesnake. Rattlesnakes, along with copperheads, cottonmouths, or water moccasins, belong to the pit viper family. 99 percent of venomous snakebites in the United States are caused by pit vipers. Coral snakes, native to the deep South, and Arizona, are responsible for the remainder of venomous bites. 

Snakebites are most common from April to October, when people spend time outdoors. White males make up 76% of snakebite victims, with 50% of victims aged between 18 and 28 years. The overwhelming majority of snakebites occur to an extremity. 

Venomous snake bites can cause symptoms ranging from mild, such as puncture wounds and local swelling, to severe, such as coagulopathy, renal failure, and shock. 

Venom 101

Not all snakebites are created equal. The amount of venom delivered by the snake depends on the amount of time that has elapsed since the last bite, the perceived level of threat by the snake, and the size of prey. The goal of releasing venom is to immobilize the victim, and begin the digestive process. 

There are two classifications of snake venom: 

  1. Hemotoxic - attacks blood and tissue
  2. Neurotoxic - damages or destroys nerve tissue

Pit vipers deliver hemotoxic venom. Coral snakes deliver neurotoxic venom. 

Venom contains proteins and enzymes that destroy tissue allowing venom to spread. Hemolytic enzymes destroy red blood cell membranes and muscle tissue, while thrombogenic enzymes cause coagulopathy. 

The concentration of enzymes present in venom varies by species. Copperhead bites, for example, typically result in local tissue destruction. In contrast, rattlesnake bites result in systemic toxicity. Coral snake bites may be almost unnoticeable at first, but later result in respiratory failure as a result of neurotoxins. 

Clinical Presentation

If possible, it is important to get a description of the snake from the patient. Most snakes remain within 20 feet after biting a human, and may be visualized after the bite incident. Asking the patient about the exact timing and early symptoms of the bite is imperative. Early and intense pain at the site of the bite is a sign of more significant envenomation.

The effects of snakebites range from mild, local discomfort and swelling, to life-threatening systemic complications. Children are more likely to experience significant reactions as they receive a larger amount of venom compared to body size.

Locally, patients may experience symptoms of pain, swelling, and paresthesias. Systemic symptoms of snakebite include nausea, syncope, and difficulty swallowing or breathing. Local tissue destruction is characterized by pitting edema, typically developing over 6 to 12 hours, erythema, discoloration, bullae, and/or contusions. Systemic envenomation may be marked by hypotension, petechiae, epistaxis, hemoptysis, paresthesia, and respiratory distress.  

Evaluation 

Lab studies for snakebite typically include a CBC, prothrombin time, INR, creatinine phosphokinase (CPK), and chemistries including creatinine, BUN, and electrolytes. Patients with systemic symptoms should also have an arterial blood gas and lactate level. Urinalysis is also helpful to evaluate for myoglobinuria. Labs should not be drawn from the affected extremity. 

Additionally, consider ordering an X-ray of the affected area to rule out a retained foreign body, such as a fang. A chest X-ray may also be necessary in patients with respiratory symptoms to rule out pulmonary edema. 

Treatment

Patients presenting with snakebites should be evaluated in the emergency department. Poison control must be consulted to guide treatment. Stabilization is the first priority in treating snakebite victims. Assess the patient's airway, breathing, and circulation. Jewelry or constructing clothing should be removed from the affected extremity. Restrict activity of the affected extremity and immobilize the area with a splint if possible.

In the initial evaluation of the patient, the bite size and at least two other proximal locations should be measured to assess discoloration. The circumference of the affected limb should also be measured. Reassess limb circumference and size of the affected area every 15-30 minutes until swelling is no longer progressing. Check distal pulses regularly. Consult a specialist immediately if there is concern for developing compartment syndrome. Finally, the bite wound must be cleaned, and if indicated, a tetanus shot administered. 

Snakebite envenomation can be measured using the Snakebite Severity Scale. Treatment measures depend on severity of the condition. Monitor the patient's condition frequently, as symptoms may develop over time requiring a change in the course of treatment. 

Patients with less severe envenomation should be monitored for a minimum of 12 hours following a pit viper bite. If swelling has not progressed, and no signs of coagulopathy are present after 12 hours of observation and serial labs, the patient may be sent home with strict follow-up instructions. Patients with coral snakebites must be observed for a minimum of 24 hours given their potential for neurotoxicity. 

Patients with moderate to severe envenomation are eligible to receive CroFab antivenom. Symptoms qualifying as moderate include severe local pain, edema, nausea, vomiting, and/or alterations in lab values. Severe symptoms include petechiae, hypotension, hypoperfusion, ecchymsis, renal dysfunction, and abnormal coaguopathy results. Antivenom is most effective if administered within the first 4 hours after the snakebite, but can be effective for the first 24 hours after the injury. 

While mortality from snakebites is quite low in the United States, complications such as compartment syndrome, and shock can occur. Healthcare providers must carefully assess and monitor patients presenting with snakebites to ensure the best possible outcome. 

 

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