First aid measures should never substitute for definitive medical care or delay the administration of antivenom (Table 212-1). Take all patients bitten by a pit viper to a healthcare facility. Avoid dangerous first aid treatments such as suction and incision. Do not use Snake Bite Kit and similar products because they contain cups that produce little suction and seal poorly on digits. The blade in the kit, or any method of incision, can injure digital nerves, arteries, and tendons. The Sawyer Extractor (Sawyer Products, Inc., Safety Harbor, FL) suction pump is said to remove venom without incision, but safety and efficacy of the product are questioned.4 Electric shock treatment of the bite site is dangerous and ineffective and can cause electrical injuries. Ice water immersion worsens the venom injury.
TABLE 212-1Recommended First Aid Measures for Snakebite ||Download (.pdf) TABLE 212-1 Recommended First Aid Measures for Snakebite
Retreat well beyond striking range. Many victims are bitten again while trying to capture the snake.
Remain calm. Movement will increase venom absorption.
Immobilize the extremity in a neutral position below the level of the heart.
Ensure prompt transport to a medical facility whether or not there are signs of envenomation.
Constriction bands (see text) can be applied if there is no nearby medical facility.
Do not use tourniquets because they obstruct arterial flow and cause ischemia. Constriction bands may be useful, especially when immediate medical care is not available. A constriction band is an elastic bandage or Penrose drain, thick rope, or piece of clothing wrapped circumferentially above the bite, applied with enough tension to restrict superficial venous and lymphatic flow while maintaining distal pulses and capillary filling. Apply the band snugly but loose enough to avoid arterial compromise. A constriction band can delay venom absorption without causing increased swelling.5
In the prehospital phase, immobilize the limb, establish IV access in another limb, administer oxygen, and transport the victim to a medical facility. Do not remove tourniquets or constricting bands until antivenom is available.
Institute advanced life support measures as indicated. If the patient is hypotensive, rapidly administer IV isotonic fluids. Continue to immobilize the limb in a neutral position during transport to reduce further venom absorption. Consult with a physician or poison control center familiar with the management of snake envenomation for most cases.
Antivenom is the mainstay of therapy for venomous snakebites2,6 (Table 212-2). Antivenom is composed of heterologous antibodies derived from the serum of animals immunized with the appropriate snake venoms. The antibodies bind and neutralize the venom molecules.
TABLE 212-2Clinical Features and Treatment of Reptile Envenomation ||Download (.pdf) TABLE 212-2 Clinical Features and Treatment of Reptile Envenomation
|Reptile ||Clinical Findings ||Antivenom |
|Crotaline snake (pit viper) || |
Local tissue injury
|Crotalidae Polyvalent Immune Fab |
|Coral snake ||Neurologic dysfunction ||Antivenom (Micrurus fulvius) |
|Elapid snake || |
Coagulopathy for some species
Systemic effects, primarily neurologic dysfunction
Cardiac arrhythmias and dysfunction
Local injury for some species
|Each species has monovalent or polyvalent antivenoms |
|Gila monster || |
Local pain and swelling
Infections from retained teeth
|No antivenom available |
Crotalidae Polyvalent Immune Fab (Ovine) (FabAV) is used in the United States; equine-derived products (Antivenom [Crotalidae] Polyvalent; see below) are no longer available. FabAV is produced by immunizing herds of sheep with one of four crotaline snake venoms: eastern diamondback (Crotalus adamanteus), western diamondback (Crotalus atrox), Mojave (Crotalus scutulatus), or cottonmouth (Agkistrodon piscivorus). The immune serum is harvested from each group and then digested with papain to produce antibody fragments (Fab and Fc). The more immunogenic Fc portion of the antibody is eliminated during purification. The four individual monospecific Fab preparations are combined to form the final antivenom product.
Treat all patients with bites who develop progressive signs and symptoms with antivenom promptly. Progression is defined as worsening of local injury (e.g., pain, ecchymosis, or swelling), abnormal results on laboratory tests (e.g., worsening platelet count, prolonged coagulation times, or decreased fibrinogen level), or systemic manifestations (e.g., unstable vital signs or abnormal mental status) (Table 212-3).
TABLE 212-3Laboratory Evaluation in Crotaline or Elapid Snakebite ||Download (.pdf) TABLE 212-3 Laboratory Evaluation in Crotaline or Elapid Snakebite
INR or prothrombin time*
Fibrin degradation product levels
Serum electrolyte levels
Creatine kinase level
Arterial blood gas analysis‡
Administer FabAV IV as a large "initial control" dose followed by three smaller maintenance doses (Figure 212-2). Initial control is cessation of progression of three clinical evaluation parameters: local effects, systemic effects, and hematologic abnormalities. The initial dose is four to six vials, which may be repeated to establish initial control of the envenomation. After initial control has been established, two-vial maintenance doses are recommended (Figure 212-2). After reconstitution, dilute each dose of FabAV in 250 mL of crystalloid and infuse over 1 hour. The total volume, but not the number of vials, may be reduced in small children.7 If IV access is unavailable, consider intraosseous administration.
Administration of Crotalidae Polyvalent Immune Fab (Ovine) (FabAV). *Initial control is cessation of progression of all components of envenomation: local effects, systemic effects, and coagulopathy.
Do not inject antivenom directly into a digit, or IM, because venom-induced hypovolemia may retard absorption of antivenom. Hospital pharmacies in those regions of the United States where venomous snakes are prevalent should maintain adequate stocks of antivenom. Unfortunately, many hospitals stock insufficient amounts of antivenom, even in endemic areas.8
The package insert is useful as a guide for antivenom preparation. Give antivenom in a critical care facility such as an ED or intensive care unit, under direct physician supervision, and with resuscitative drugs and equipment immediately available (including epinephrine). The incidence of acute reactions to FabAV is <10%.9 If an acute allergic reaction occurs, stop the infusion immediately and administer antihistamines (both histamine-1 and histamine-2 receptor blockers). Epinephrine should be readily available and administered for anaphylaxis.
Continue to observe for progression of edema and systemic signs of envenomation during and after antivenom infusion. Measure limb circumference at several sites above and below the bite, and outline the advancing border of edema with a pen every 30 minutes. These measures serve as an index of the progression as well as a guide for antivenom administration. Repeat laboratory determinations every 4 hours or after each course of antivenom therapy, whichever is more frequent. Additional doses of FabAV may be warranted if the patient's condition worsens. FabAV has been formally tested only in the treatment of rattlesnake bites. Initial case reports support its efficacy in treatment of copperhead snakebites.10
The value of aggressive supportive care cannot be overemphasized. Administer isotonic fluid resuscitation followed by vasopressor agents for hypotension. Antivenom is the best treatment for hematologic abnormalities, but if active bleeding occurs, blood component replacement may be necessary. Compartment syndrome is another complication of snakebite: increased compartment pressure may occur when venom is injected or spreads into a compartment. This is often manifested by severe pain, localized to a compartment and usually resistant to opiate analgesia. Table 212-4 presents the suggested treatment of compartment syndrome.11 The use of fasciotomy is controversial, and there is no firm evidence supporting its use.
TABLE 212-4Management of Compartment Syndrome Caused by Crotalinae Snake Envenomation*† ||Download (.pdf) TABLE 212-4 Management of Compartment Syndrome Caused by Crotalinae Snake Envenomation*†
Determine intracompartmental pressure.
If pressure is not elevated, continue standard management.
If signs of compartment syndrome are present and compartment pressure is >30 mm Hg:
Administer mannitol, 1–2 grams/kg IV over 30 min.
Simultaneously administer additional FabAV, 4–6 vials IV over 60 min.
If elevated compartment pressure persists another 60 min, consider fasciotomy.
Clean the bite wound and determine the need for tetanus immunization. Obtain wound specimens for culture and administer antibiotics if signs of infection are present. Although antibiotic prophylaxis is recommended by some authors, the data available do not support its use.12 Steroids are not effective and could be harmful. Steroids should be reserved for the treatment of allergic reactions or serum sickness.
Serum sickness develops in about 5% of patients after FabAV treatment. The symptoms are fever, rash, and arthralgias. Start oral prednisone, 1 milligram/kg/d, and taper over 1 to 2 weeks.