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Emergency and Acute Medicine – Snake Envenomation
Snake envenomation is a medical emergency caused by the injection of venom, most commonly from pit vipers, which contain proteolytic enzymes and thrombin-like substances. These toxins cause local tissue destruction and systemic coagulopathy known as venom-induced consumption coagulopathy (VICC). While extremity bites are most common, bites to the head, neck, or trunk are more severe. Notably, up to 25% of pit viper bites are “dry bites” and do not result in envenomation.
In the United States, pit vipers (rattlesnakes, copperheads, and cottonmouths) account for the vast majority of envenomations. Coral snakes, though less common, produce primarily neurotoxic venom. International and exotic snakes may also be encountered, particularly in zoos or private collections. Children are at higher risk for severe toxicity due to smaller body mass.
Local symptoms of pit viper bites typically include one or two puncture wounds, immediate pain, swelling, and progressive edema. Over time, ecchymosis, petechiae, and hemorrhagic blisters may develop. Regional lymphadenopathy is common. Systemic symptoms may include weakness, nausea, diaphoresis, metallic taste, and neurologic findings such as paresthesias or fasciculations. Severe envenomation can lead to coagulopathy, hypotension, pulmonary edema, kidney injury, and cardiac dysfunction. Coral snake envenomation may initially show minimal local findings but can cause delayed neurologic symptoms such as weakness, diplopia, and respiratory failure.
Evaluation requires careful and repeated physical examination, including marking the margins of swelling to monitor progression. Laboratory studies include CBC, coagulation profile, fibrinogen, electrolytes, renal function, creatine phosphokinase, and urinalysis. These help assess severity and complications such as coagulopathy or rhabdomyolysis.
Prehospital care focuses on safety and supportive measures. The patient should move away from the snake, minimize activity, and keep the affected limb immobilized at heart level. Constrictive items should be removed. Harmful interventions such as incision, suction, tourniquets, cryotherapy, or electrical treatment should be avoided, as they worsen outcomes.
Initial management in the emergency setting follows airway, breathing, and circulation principles, along with fluid resuscitation to maintain renal perfusion. Pain is managed with IV opioids. Tetanus prophylaxis should be updated, but routine antibiotics and steroids are not indicated unless treating antivenom reactions.
Antivenom is the cornerstone of treatment for significant envenomation. Indications include progressive swelling, systemic toxicity, coagulopathy, or unstable vital signs. CroFab is the primary treatment for North American pit viper envenomation. Initial dosing is typically 4–6 vials IV, with higher doses for severe cases. Response is assessed after infusion, and additional or maintenance dosing may be required. Pediatric patients receive the same dosing as adults.
Patients must be monitored closely for allergic reactions to antivenom. If reactions occur, treatment includes antihistamines, corticosteroids, fluids, and epinephrine if severe. Decisions about restarting antivenom should involve a toxicologist or poison control center.
Patients with moderate to severe envenomation or those receiving antivenom require admission, often to the ICU. Even asymptomatic patients with potentially venomous bites should be observed for several hours. Discharge is appropriate only if there are no signs of envenomation after observation and laboratory evaluation remains normal.
Key points include avoiding harmful first-aid measures, recognizing that symptoms may initially be mild, administering antivenom promptly when indicated, and ensuring close monitoring for progression or complications.
Snake envenomation is a medical emergency caused by the injection of venom, most commonly from pit vipers, which contain proteolytic enzymes and thrombin-like substances. These toxins cause local tissue destruction and systemic coagulopathy known as venom-induced consumption coagulopathy (VICC). While extremity bites are most common, bites to the head, neck, or trunk are more severe. Notably, up to 25% of pit viper bites are “dry bites” and do not result in envenomation.
In the United States, pit vipers (rattlesnakes, copperheads, and cottonmouths) account for the vast majority of envenomations. Coral snakes, though less common, produce primarily neurotoxic venom. International and exotic snakes may also be encountered, particularly in zoos or private collections. Children are at higher risk for severe toxicity due to smaller body mass.
Local symptoms of pit viper bites typically include one or two puncture wounds, immediate pain, swelling, and progressive edema. Over time, ecchymosis, petechiae, and hemorrhagic blisters may develop. Regional lymphadenopathy is common. Systemic symptoms may include weakness, nausea, diaphoresis, metallic taste, and neurologic findings such as paresthesias or fasciculations. Severe envenomation can lead to coagulopathy, hypotension, pulmonary edema, kidney injury, and cardiac dysfunction. Coral snake envenomation may initially show minimal local findings but can cause delayed neurologic symptoms such as weakness, diplopia, and respiratory failure.
Evaluation requires careful and repeated physical examination, including marking the margins of swelling to monitor progression. Laboratory studies include CBC, coagulation profile, fibrinogen, electrolytes, renal function, creatine phosphokinase, and urinalysis. These help assess severity and complications such as coagulopathy or rhabdomyolysis.
Prehospital care focuses on safety and supportive measures. The patient should move away from the snake, minimize activity, and keep the affected limb immobilized at heart level. Constrictive items should be removed. Harmful interventions such as incision, suction, tourniquets, cryotherapy, or electrical treatment should be avoided, as they worsen outcomes.
Initial management in the emergency setting follows airway, breathing, and circulation principles, along with fluid resuscitation to maintain renal perfusion. Pain is managed with IV opioids. Tetanus prophylaxis should be updated, but routine antibiotics and steroids are not indicated unless treating antivenom reactions.
Antivenom is the cornerstone of treatment for significant envenomation. Indications include progressive swelling, systemic toxicity, coagulopathy, or unstable vital signs. CroFab is the primary treatment for North American pit viper envenomation. Initial dosing is typically 4–6 vials IV, with higher doses for severe cases. Response is assessed after infusion, and additional or maintenance dosing may be required. Pediatric patients receive the same dosing as adults.
Patients must be monitored closely for allergic reactions to antivenom. If reactions occur, treatment includes antihistamines, corticosteroids, fluids, and epinephrine if severe. Decisions about restarting antivenom should involve a toxicologist or poison control center.
Patients with moderate to severe envenomation or those receiving antivenom require admission, often to the ICU. Even asymptomatic patients with potentially venomous bites should be observed for several hours. Discharge is appropriate only if there are no signs of envenomation after observation and laboratory evaluation remains normal.
Key points include avoiding harmful first-aid measures, recognizing that symptoms may initially be mild, administering antivenom promptly when indicated, and ensuring close monitoring for progression or complications.
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