Snakebite

Snake envenomation is a rare but potentially serious medical emergency in the United States. Internationally, approximately 50 000 people die every year from snakebites. In the United States, approximately 5 people die per year from the 7000 to 8000 bites that typically occur, but morbidity is very common. Prompt identification and appropriate management are essential to reduce complications such as tissue cytotoxicity, coagulopathy, or neurotoxicity. More than 95% of venomous snakebites in the United States are from Crotalidae snakes, also called pit vipers (eg, rattlesnakes, water moccasins/cottonmouth, copperheads). Pit vipers have a triangular head, elliptical eyes, and a pit between each eye and nostril. The remainder of venomous snakebites in the United States are largely attributed to the Elapidae family, which includes the coral snake—famously recognized by the mnemonic “red on yellow, kill a fellow; red on black, venom lack.” Unlike pit vipers, Elapidae bites produce prominent neurotoxicity with minimal local reactions and are treated with species-specific antivenom. According to the North American Snakebite Registry (NASBR), snakebites are more common in men (69%) and affect children younger than 12 years of age in nearly 30% of cases. Most pediatric bites occur on the lower extremities, often without footwear; in one study, one-quarter of patients with lower extremity bites were barefoot, and more than 61% wore sandals or flip-flops. Preventive measures against snakebites can be as simple as wearing closed-toe shoes outside or taking extra precaution to look before stepping and to use extreme caution reaching into holes or under logs or brush. Additionally, it is a good idea to teach children not to provoke or pick up snakes. Snakes primarily produce venom to target prey, but it is also used in self-defense. When venom is released, the clinical effects are a result of both the volume of toxin released and the potency of the venom.This In Brief outlines the appropriate response to a Crotalidae snakebite in a medical setting, how to differentiate venomous bites that warrant antivenom, and expected outcomes. Variations in regional practice patterns exist in the administration of antivenom, and consensus treatment guidelines will be discussed here. Because this is a rare event for many clinicians, early consultation with Poison Control is essential. Medical toxicologists can provide information and guidance for treatment based on the types of snakes in the region. Initial management following a snakebite begins with scene safety and getting to a safe location away from the snake followed by stabilization. After removing any jewelry or tight-fitting items, the bitten limb should be immobilized and kept at or slightly below heart level in the prehospital setting to minimize absorption of the snake venom by the lymphatic system. Constriction bands, ice, suction, and wound incision are strongly discouraged, as these strategies have been shown to cause more tissue damage. Medical attention should be sought as soon as possible and preferably within 6 hours of the bite. In the emergency department (ED), clinicians should focus on overall assessment, pain management, optimal limb positioning, and obtaining laboratory tests. Nonsteroidal medications should initially be avoided because of potential effects of the venom on the coagulation cascade and the risk of increased bleeding. Once patients are in the ED, it is expected that the cytotoxic effects of the venom have started and will cause increasing edema; thus, it is recommended to elevate the affected limb in the ED and avoid joint flexion. Initial measurement of the limb and subsequent measurement of swelling progression are critical to determine whether antivenom is indicated. Complete blood count, prothrombin time, partial thromboplastin time, and fibrinogen are generally recommended every 6 hours, although recommendations may vary on the initial symptoms and regional practice patterns. Tetanus prophylaxis should be updated when indicated. Not all bites by venomous snakes result in envenomation. “Dry” bites, without venom injection, can occur but can be challenging to differentiate clinically. Most “dry” bites present with a wound but no other signs of systemic envenomation; however, these patients still warrant observation for any development of symptoms or signs for a period of at least 8 hours. Crotalidae venomous bites may produce 1 or more of the following: rapidly progressive swelling, local ecchymosis or bullae, hematologic toxicity such as coagulopathy and thrombocytopenia, or neurotoxicity, including paresthesia or fasciculations, which develop within the first 12 to 24 hours. Envenomation severity can vary by species and even within 1 species. For example, copperhead bites often cause local tissue injury and the sensation of a metallic taste, while Mojave rattlesnakes may cause neurotoxicity. Hematotoxicity and neurotoxicity are more closely associated with rattlesnake bites. Patients should be monitored for symptoms and signs that are local or systemic or hematologic. Local symptoms include pain, swelling, ecchymosis, erythema, and, less commonly, necrosis. Systemic signs can include vomiting, hypotension, tachycardia, diarrhea, angioedema, lethargy, paresthesias, muscle weakness, fasciculations, and headache. In children, who may be unable to articulate symptoms, swelling, and unexplained systemic signs such as vomiting or altered mental status may signal systemic involvement. Finally, hematologic symptoms can include bleeding beyond the puncture site.The decision to treat with antivenom is based on clinical presentation and symptom progression. Antivenom (specifically Crotalidae Polyvalent Immune Fab ovine CroFab or Anavip) is indicated for the following: (1) progressive swelling; (2) hematologic abnormalities, including low fibrinogen or platelets and elevated prothrombin time; or (3) systemic symptoms, such as hypotension, gastrointestinal symptoms, or neurotoxicity. The clinical decision to give antivenom balances the benefit of antivenom against the high cost and potential antivenom side effects. Children and adults both receive an initial dose of 4 to 6 vials, infused over an hour, with repeat dosing if clinical control is not achieved. For severe cases with shock or uncontrolled bleeding, higher initial doses (8–12 vials) can be appropriate and guided by the expertise of Poison Control. Contrary to typical weight-based dosing for children, the pediatric dose of antivenom is the same as the adult dose because the antivenom neutralizes the amount of venom injected. Patients should be closely monitored during antivenom infusion for adverse reactions, including anaphylaxis, which requires prompt treatment with epinephrine and infusion cessation. Milder reactions that share some symptoms with anaphylaxis, such as pruritus and urticaria, are nonallergic infusion-related reactions and are estimated to occur in up to 6% of patients. The treating physician should examine the patient and repeat labs within 1 hour after antivenom is administered to evaluate treatment response. It is rare to require more than 2 doses of antivenom to achieve initial control of venom effects. Repeating the dose is sometimes used to prevent the recurrence of limb swelling, although this practice is institution dependent. Unified treatment guidelines emphasize the early use of antivenom when indicated and discourage prophylactic antibiotics, nonsteroidal anti-inflammatories, steroids, and fasciotomy. Observation alone, for a minimum of 8 hours, is appropriate for apparent dry bites or mild envenomation with no progression of swelling and absence of systemic symptoms. Compartment syndrome can occur but is an exceedingly rare complication of snake envenomation and requires pressure measurements to diagnose and manage. Once initial control is achieved—defined by stable laboratory values, no progression of swelling, and improving systemic signs—patients should be monitored for a period of observation ranging from 8 to 24 hours. At discharge, patients should be instructed to return for worsening swelling that is not improved by elevation or abnormal bleeding. Patients bitten by a rattlesnake or with coagulopathy should be counseled on bleeding precautions, including avoiding contact sports, elective surgery, or dental work for 2 weeks, and that coagulopathy tests may need to be repeated. Families should also be educated on the signs and symptoms of serum sickness in response to the antivenom that may develop 5 to 14 days after treatment. Serum sickness typically presents as an influenza-like illness with a rash and is estimated to occur in 5% to 10% of patients treated with antivenom. It is generally mild and easily treated with antihistamines and steroids. The prognosis for snakebite victims in the United States is favorable after early intervention. In the NASBR review, no deaths were reported during the study period of 2 years. Rehospitalization occurred in 4% of cases, usually because of recurrence of swelling or hematologic abnormalities. Children may be at higher risk for systemic effects from a given venom dose, given their smaller vascular volumes. Most children fully recover after appropriate care, although long-term complications such as tissue loss, chronic pain, or complex regional pain syndrome can occur, particularly when care is delayed or suboptimal.In summary, while infrequent, snakebites demand a structured and evidence-based approach to evaluation and treatment. Prompt recognition of envenomation, early use of antivenom when indicated, and close follow-up are critical. Pediatric providers should be familiar with these principles and work closely with Poison Control and toxicology experts when managing cases.Comment: Snakebites are an international problem, and The World Health Organization in 2017 identified snake envenomation as a category A neglected tropical disease. This has allowed for more research on the topic and potential enhanced funding for development of antivenom. I found it fascinating that snakebites occur on every continent except Antarctica. While a rarer diagnosis for those who practice in urban settings, it can be challenging to make the diagnosis if the bite sight shows only a single fang mark, the puncture site is obscured because of localized edema, and there is only an abrasion, as seen with a “dry bite.” Challenges with pediatric patients include the history they are able to give—whether they saw the snake and can accurately identify the type of snake. I did care for a 10-year-old in my urban practice who had had a snakebite by a copperhead snake. In this case, we were fortunate, as he was a good observer and historian. He did meet the criteria for administration for antivenom, and this In Brief describes the steps we needed to follow to ensure high-quality care. The bite was on his leg, and he experienced quite marked swelling. Because this is a fairly rare event for many clinicians, consulting with Poison Control and toxicologists is an essential resource for information to provide guidance and better understanding of local and geographic aspects of the types of snakes in the region. Having witnessed the fear in both my patient and his parents following the dramatic reaction his body exhibited from the bite, it did make me more mindful of preventive strategies. While they are not foolproof, teaching both children and adults to not step in a hole where they cannot see the bottom or put their hand in a hole, the benefit of wearing closed-toe shoes, and to never provoke or try to pick up a snake are all good advice. I also learned a new word. One symptom of neurotoxicity is myokymia, which is eyelid twitching.Janet Serwint, MDEditor Emeritus, In Brief