Approach
Treatment for snakebites depends on whether or not envenomation has occurred and, when envenomation has occurred, the type of snake responsible. Generally speaking, four broad classes of snakebite exist, each requiring a unique approach to treatment:
Snakebite without envenomation
Domestic Crotalinae envenomation
Domestic Elapidae envenomation
Exotic or non-native snake envenomation.
Wound care and analgesia
Prehospital wound care:
Local wound care includes to rest and immobilize the bitten extremity and minimize exertion of the patient to delay centripetal spread of the venom.[31][32][33] Complete immobilization is key in that movement of the extremity leads to centripetal spread of the venom. Potentially constricting objects (i.e., rings, bracelets) should be removed as subsequent soft tissue swelling may make later removal more difficult.[34]
For venomous snakebites that do not cause local tissue damage and are neurotoxic (i.e., Elapidae or coral snakes) a pressure-immobilization bandage may be considered if the snake is definitively identified as a coral snake and not a crotaline or pit viper.[35] However, studies have demonstrated that medical personnel and lay rescuers have a low rate of applying such bandages at the appropriate pressure, which may limit their benefit.[34] An elastic bandage should be applied with 40 to 70 mmHg pressure for an upper limb or 55 to 70 mmHg pressure for a lower limb.[36] A finger should be able to pass easily underneath the bandage. Elastic bandages may be superior to crepe bandages in maintaining an ideal pressure and preventing centripetal spread of venom.[37]
The use of pressure-immobilization bandages in snakebites that do cause local tissue damage (i.e., Crotalinae or pit vipers) should be avoided as it does not improve outcomes and may increase intracompartmental pressures in the bitten extremity.[34][38]
Tourniquets should be avoided as they may increase local tissue destruction. Incising the wound should be avoided as it does not improve patient outcomes and may cause tendon damage. There is no evidence that suction cups in commercially available extractor kits improve outcome following envenomation, and they should be avoided.[34]
[Figure caption and citation for the preceding image starts]: The pressure-immobilization methodFrom Warrell DA. BMJ. 2005 Nov 26;331(7527):1244-7. [Citation ends].
Hospital wound care:
The wound should be inspected for foreign bodies (snake fangs or teeth); tendon or blood vessel damage should be considered based on clinical suspicion. The wound should be copiously irrigated and left to close by secondary intention. Adequate anesthesia is necessary to allow thorough wound exploration. Any foreign bodies should be removed. Anesthesia may be obtained with a regional nerve block or local infiltration.
The affected limb should be immobilized and elevated and the leading edge of the affected area (erythema, swelling) serially marked every 15 to 30 minutes to assess for symptom progression. The circumference of the bitten limb should be measured above and below the snakebite for later comparison and determination of subsequent swelling.[20]
A tetanus immunization or booster is indicated if the patient is not immunized or up to date. Because of the risk of infection, wound closure is relatively contraindicated.
The use of prophylactic antibiotics is not generally thought to be necessary. Prospective trials found that snakebite patients who do not receive prophylactic antibiotics do not develop wound infections, and suggest reserving antibiotics for cases where necrosis or signs of infection are present.[39][40][41][42] No infectious complications were noted in pediatric patients who abandoned prophylactic antibiotic treatment.[42] The risk of snakebite infection in immunocompromised patients is not well defined, and the use of prophylactic antibiotics may be prudent.
If prophylactic antibiotics are indicated due to the presence of necrosis or signs of infection, wound cultures following snakebite infection predominantly grow gram-negative aerobic bacilli (primarily Enterobacteriaceae) and gram-positive aerobic cocci, so antibiotic therapy should be directed against these bacteria.
If there is any uncertainty as to whether the bite was from a venomous snake, the patient should be observed for 8 to 12 hours to assess for developing toxicity. Elapidae envenomation may initially be asymptomatic, but if neurologic deficits develop they are difficult to reverse. Therefore, patients who are suspected of, but not confirmed as, having been bitten by the Texas coral snake or Eastern coral snake should be observed for 24 hours for signs and symptoms of envenomation and treated with antivenom as soon as such signs and symptoms develop.
Analgesia:
Pain may be treated with nonsteroidal anti-inflammatory drugs (NSAIDs) or with opioids if severe. Clinicians should use opioids cautiously in patients with hypotension and respiratory impairment because they may lead to further deterioration of the patient's condition.
NSAIDs should be avoided in patients with symptomatic Crotalinae envenomation or with clinical or laboratory evidence of coagulopathy as they may increase the risk of hemorrhage.
Snakebite without envenomation
Occurs when the snake responsible for the injury is nonvenomous or when a venomous snake does not inject venom into its victim (known as a "dry" bite). Crotalinae snakebites are frequently dry.[1][43] All Crotalinae snakebites should be observed for 8 to 12 hours for signs of local or systemic toxicity. Prior to patient discharge, a disseminated intravascular coagulation panel and complete blood count should be repeated to exclude developing systemic toxicity. If the patient remains asymptomatic and laboratory studies do not reveal systemic toxicity, it can be concluded that it was a dry bite. The exception is patients bitten by the Mojave rattlesnake, who should be admitted and require 12 to 24 hours' observation.
All Elapidae snakebites should be observed for a 24-hour period. Snakebite casualties bitten by nonvenomous snakes may be discharged home after local wound care.
Domestic Crotalinae envenomation
Patients with minimal swelling at the bite site or without progressive worsening of local symptoms should be observed and antivenom should not be administered. Patients bitten by crotalines other than the Mojave rattlesnake may be discharged after 8 to 12 hours of observation if they are asymptomatic. Patients bitten by the Mojave rattlesnake should be admitted for observation for at least 12 to 24 hours as delayed neurologic sequelae may occur. The Mojave rattlesnake is a crotaline with predominantly neurologic sequelae and less prominent local tissue effects. Patients with local or systemic symptoms should be admitted to an intensive care unit to monitor for hypotension, bleeding, and compartment syndrome. Patients should be closely monitored for developing respiratory insufficiency.
Consideration of Crotalidae antivenom
Two antivenoms are available in the US: Crotalidae polyvalent immune Fab (ovine) antivenom (known as CroFab®), and Crotalidae immune F(ab’)2 (equine) antivenom (known as Anavip®). Antivenom is indicated in all patients with systemic symptoms, laboratory derangements, or progressively worsening local symptoms.[20] Around 11% of Crotalinae envenomations in adults and 6% in children produce these clinical features and require antivenom.[42][44]
Clinicians should closely monitor patients for allergic reactions, including anaphylaxis, and serum sickness. Antivenom is contraindicated in patients with hypersensitivity to: CroFab® or Anavip® antivenom, other related antivenoms, papain, papaya, latex, dust mites, or any ingredient in the formulation. It should be used with caution in patients who have been previously treated with CroFab® or Anavip® antivenom. In patients with contraindications, the risk of antivenom administration must be weighed against the severity of envenomation.
Data from animal models shows that CroFab® is effective, with varying potency, against 10 US crotalines, while Anavip® is effective against 7 US crotalines.[45][46] However, both CroFab® and Anavip® are thought to be effective against all US crotalines.
The initial infusion should be started at a low rate (25-50 mL/hour) while assessing for any allergic reaction. If no allergic reaction occurs in the first 10 to 15 minutes, the rate of infusion may be increased. After the initial infusion is complete, the treating clinician should assess whether initial control of the envenomation (defined as complete arrest of local manifestations and normalization of vital signs and coagulation parameters) has been attained. If initial control has not been attained, the initial dose should be repeated until initial control has been achieved. Some patients with initial improvement after CroFab® antivenom administration may experience a recurrent coagulopathy hours to days later.[47][48] In one study, medically significant delayed hemorrhage was reported in approximately 0.5% of North American crotaline snakebite victims treated with CroFab® antivenom.[49] These patients may benefit from repeat administration or use of the longer-acting Anavip®, if available.[50]
Locally, the increased capillary permeability may result in elevated compartment pressures and compartment syndrome. Optimal treatment of venom-induced compartment syndrome is debated, with some authors promoting only antivenom administration and others recommending antivenom and fasciotomy.[51][52][53]
Treatment of systemic complications of Crotalinae envenomation
Hypotension, pulmonary edema, and venom-induced consumption coagulopathy require additional supportive measures.
Cardiogenic and noncardiogenic pulmonary edema may occur. Supplemental oxygen should be provided to maintain oxygenation. Patients with hypoxemia despite supplemental oxygen may require noninvasive positive pressure ventilation such as bi-level positive airway pressure. Endotracheal intubation and mechanical positive pressure ventilation may be necessary in severe pulmonary edema. Positive end-expiratory pressure may minimize atelectasis and improve oxygenation.
Crotalinae envenomation may, in some cases, cause severe coagulopathy leading to hemorrhage. Although reversal of coagulopathy generally occurs with antivenom administration, some patients may require transfusion of blood products such as platelets, packed red blood cells, or fresh frozen plasma. Routine repletion of clotting factors in patients with venom-induced consumption coagulopathy is controversial but may be associated with earlier improvement in coagulation function. It is unclear whether the improvement in coagulation function is associated with any clinical benefit.[54][55] Hypotension secondary to capillary third-spacing or cardiac myotoxicity should be treated with fluid resuscitation and vasopressors.
Domestic Elapidae envenomation
Elapidae envenomation may initially be asymptomatic, but can progress to life-threatening paralysis. Once neurologic deficits develop, they are difficult to reverse and may not immediately resolve with antivenom administration. Therefore, in addition to local wound care and close observation, treatment requires antivenom administration (antivenin, North American coral snake), unless the patient is known to have been bitten by the Arizona coral snake (where only mild symptoms may be anticipated). Pain may be treated with NSAIDs in the absence of coagulopathy, or with opioids if severe. Observation in an intensive care unit is mandatory for all patients with suspected domestic Elapidae envenomation so that progressive respiratory insufficiency may be closely followed and intubation and mechanical ventilation may be expeditiously performed if needed.
Patients who are known to have been bitten by the Texas coral snake or Eastern coral snake should receive antivenom even if they are asymptomatic.[1][26] Further doses of antivenom should be administered to patients who develop symptoms of envenomation.
Patients who have been bitten by the Arizona coral snake (also known as the Sonoran coral snake) generally develop only mild symptoms. Antivenom is not typically used. In the unlikely event of a severe Arizona coral snake envenomation, there is no evidence for antivenom efficacy and the clinician should weigh the risks and benefits of antivenom administration in that patient.
The antivenom consists of equine immunoglobulin G. A history of atopy or allergy to horses or horse serum is a relative contraindication to the antivenom. A skin test to evaluate for allergic reaction to the antivenom should be performed prior to antivenom administration. Vial administration is either by slow piggyback injection into a wide-open line of normal saline or by dilution in 250 mL of normal saline and running it wide-open. When giving the initial dose, the treating clinician should start by infusing slowly while monitoring for allergic reaction. Additional vials should be administered as needed to control signs or symptoms of Elapidae envenomation.
Exotic (or non-native) snake envenomation
Exotic snakebites and envenomations present unique problems. They are considered exotic because exposure to these snakes is typically due to their presence in a collection (e.g., zoo, private collector). Native or domestic species are not considered exotic by virtue of their being extant in the environment. Difficulties with snake identification, and with procuring and administering antivenom, may all complicate management. Management of exotic snake envenomation is variable and should be performed in consultation with a medical toxicologist. Symptoms of exotic snake envenomation will vary with the species of snake involved and may not be well defined in the medical literature. Close observation in an intensive care unit may prevent unexpected morbidity or mortality.
In addition to local wound care and close observation, exotic snake envenomation requires treatment with antivenom, if obtainable, and supportive measures. Antivenom for exotic snakes is not commercially available in the US; however, zoos, herpetologists, and certain specialist emergency services, such as the Miami-Dade Fire Rescue Venom Response Unit, have antivenom on hand for a variety of exotic snakes. Miami-Dade Fire Rescue: Venom Response Unit Opens in new window Foreign medical institutions may have antivenom for species native to their areas.
Because of the variety of exotic poisonous snakes, and interspecies variations in venom, clinical presentation and supportive measures will vary significantly among patients:
Envenomation by exotic snakes of the family Viperidae may cause systemic derangements similar to those caused by their Crotalinae relatives. Clinicians should be aware of the risks of pulmonary edema, hypotension, and coagulopathy, and treat accordingly.
Envenomation by exotic Elapidae snakes may produce symptoms similar to those produced by domestic elapids.
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