Bites and envenomations account for 3% of phone calls to poison control centers.¹ In North America, venomous animals vary by specific region and include varied terrestrial vertebrates and invertebrates. Venomous bites are of particular concern in the pediatric population, with the highest morbidity and mortality occurring in smaller patients. Diagnosis and management strategies for envenomation vary according to the type of animal, specific toxic properties of the venom, location of the bite, time elapsed since exposure, appearance of the wound, systemic symptoms, size of the child, and history and physical examination findings (Table 176-1). It is important to keep in mind that unwitnessed bites can occur in younger children. This chapter specifically addresses the presentation and management of common snake bites, as well as black widow and brown recluse spider bites.

In North America, the most common venomous snakes belong to the Viperidae family (Crotalinae subfamily) and are commonly referred to as pit vipers.

Common features of their general appearance that differentiate them from nonpoisonous snakes include a triangular head, vertically positioned elliptical pupils, heat-sensing nostril pits, and a single row of scales at the tail. In North America, common crotaline snakes include (1) eastern and western diamondbacks and other multiple species of rattlesnakes, (2) copperheads, and (3) water moccasins (also called cottonmouths); envenomation by rattlesnakes is usually more severe. In addition to pit vipers, coral snakes (Elapidae family) can be found in the southeastern and southwestern United States. Coral snake envenomation is less common than pit viper bites but can cause serious neurologic dysfunction.

CLINICAL PRESENTATION

About 75% of snake bites, from venomous snakes, occur with envenomation. It is important to remember that a snake bite deposits the same amount of venom regardless of the size of the victim. Therefore a smaller patient will have a more significant venom load per kilogram and will be at higher risk for morbidity and mortality than larger children and adults. Crotaline venom contains a mixture of multiple enzymes and toxic substances. It is usually deposited subcutaneously, but rarely there can be subfascial or intravascular deposition. Local effects start approximately 15 to 30 minutes after the bite and include pain, paresthesias, numbness, edema, ecchymosis, necrosis, bleeding, and hemorrhagic blisters and blebs. Swelling can be extensive and is of particular concern if respiratory obstruction occurs from bites to the mouth, face, or neck. Although the appearance of a swollen bite site may mimic compartment syndrome, the subcutaneous location of envenomation makes compartment syndrome unlikely.

Systemic symptoms can include diaphoresis, lightheadedness, chills, nausea, and vomiting. Rhabdomyolysis is a rare complication. With crotaline snakes, systemic effects primarily involve the hematologic system, with laboratory abnormalities typical of disseminated intravascular coagulation: decreased fibrinogen and platelets and increased prothrombin and partial thromboplastin times, fibrin split products, and D-dimer. Certain crotaline snakes (Mojave rattlesnakes) also have neurotoxic venom. Coral snake envenomation has neurologic sequelae as its primary feature and minimal local effects. Neurologic symptoms of Mojave and coral snake envenomation can include fasciculations, paresthesias, cranial nerve deficits, and muscular weakness that could involve the respiratory muscles (Table 176-2).

DIAGNOSTIC EVALUATION

For every envenomation, initial management includes stabilization of respiratory and cardiovascular status and local wound care. Local wound care with irrigation is important. Venom should never be removed by oral suction because it has not been proven to be effective and may increase the risk for infection. Use of tourniquets is not recommended, but the affected location should be immobilized and not elevated to minimize mobilization of toxins. Tetanus immunization status should be confirmed and a toxoid administered if indicated. Prophylactic antibiotics have not been shown to be helpful. Laboratory markers that should be monitored for suspected crotaline envenomation include complete blood count (CBC), prothrombin and partial thromboplastin times, fibrinogen, fibrin split products, D-dimer, electrolytes, blood urea nitrogen, creatinine, creatine kinase, urinalysis, and type and screen.

MANAGEMENT

Crotaline antivenom is indicated for swelling that compromises local structures such as in the hands and, in particular, airway-compromising obstruction at the neck or face, and for neurologic and hematologic abnormalities. Crotalidae polyvalent immune Fab–ovine (CroFab) is an ovine antibody preparation that has become the preferred antivenom for the treatment of envenomation by North American crotaline snakes and is safe for use in the pediatric population.^2,3 It is less immunogenic⁴ and better tolerated than the older horse serum–derived antivenoms, which have a high incidence of anaphylaxis and serum sickness. Crotaline polyvalent immune Fab is administered at a dose sufficient to neutralize the injected venom, and therefore the recommended dose is identical for patients of all sizes and ages. A consensus guideline was created to support a unified treatment algorithm.⁵ Four to six vials should be administered initially, with additional vials given to achieve clinical control of the envenomation syndrome. The Fab antivenom has a short pharmacodynamic half-life, and the manufacturer recommends maintenance dosing at 6-hour intervals. If Crotalidae polyvalent immune Fab is not available, patients may be treated with Crotalidae antivenom-equine. Fasciotomy is not indicated except for the rare situation of subfascial envenomation with resultant compartment syndrome that is not ameliorated with antivenom administration.