Worldwide, approximately 90,000 to 125,000 fatal snakebites are sustained each year.^1,2 Of the 120 snake species indigenous to the United States, approximately 20% are venomous (Table 134-1). Venomous snakes are classified into two families: Viperidae and Elapidae. Crotalinae is a subfamily of Viperidae better known as pit vipers due to the heat-sensing organs on either side of the head. The Crotalinae subfamily includes three genera: Crotalus (rattlesnakes), Agkistrodon (copperheads and cottonmouths), and Sistrurus (pigmy rattlesnakes and massasaugas).³ While copperhead (Agkistrodon contortrix) and cottonmouth (A. piscivorus) snakes are primarily found in the southern and eastern United States, several species of rattlesnake are found throughout the continental United States. Although snakebites are typically underreported, it is estimated that 8000 crotaline envenomations occur in the United States annually. Approximately 30% of snakebites called to US poison control centers involve patients younger than 20 years, with 12% of all cases being children aged 9 years or younger.⁴

ANATOMY

A few anatomic characteristics differentiate venomous pit vipers from nonvenomous snakes. Pit vipers possess a triangular or arrow-shaped head, whereas nonvenomous North American snakes have a smooth, tapered body and narrow head. Crotalids have facial pits between the nostril and the eye that serve as heat and vibration sensors, enabling the snake to locate prey (Fig. 134-1). While nonvenomous snakes typically possess round pupils, pit vipers have vertical or elliptical pupils. Members of the genus Crotalus also have characteristic tail rattles, depending on maturity, and a single row of ventral anal scales.⁵

PATHOPHYSIOLOGY

Since snakes are defensive animals and rarely attack, they will remain immobile or even attempt to retreat if given the opportunity. Bites most commonly occur in small curious children or in individuals who handle or harass the snake. Because of their small body weight, infants and young children are relatively more vulnerable to severe envenomation. The severity of envenomation also depends on the location of the bite. Bites on the head, neck, or trunk can be more severe than extremity bites.⁶ Bites on the upper extremities are most common and potentially more dangerous than those on the lower extremities, although lower extremity bites may result in delayed clinical signs of toxicity. Male children are more likely than female children to suffer Crotaline snakebites that require antivenom therapy. Males are also more likely to be bitten in the upper extremities.⁷ Direct envenomation into an artery or vein is associated with a higher mortality rate.

It is important to remember that when envenomation occurs, the smaller pediatric patient is typically exposed to a greater milligram per kilogram venom load than an adult, so treating clinicians should anticipate a higher likelihood of systemic symptoms. Intravenous antivenom is always the first-line therapy and dosing should be targeted toward the potential venom load and its clinical sequelae, as opposed to the patient’s weight.⁸

Crotaline venom is a complex mixture of enzymes that primarily function to immobilize, kill, and digest the snake’s prey. Proteolytic enzymes cause muscle and subcutaneous necrosis because of a trypsin-like action. Hyaluronidase decreases the viscosity of connective tissue, phospholipase provokes histamine release from mast cells, and thrombin-like amino acid esterases act as defibrinating anticoagulants.⁹ The major toxic effects occur within the surrounding tissue, blood vessels, and blood components.

CLINICAL PRESENTATION

Local cutaneous changes classically include one or two puncture marks with pain and swelling at the site, while nonvenomous North American snakes may leave a horseshoe-shaped imprint of multiple teeth marks. Approximately 25% of all pit viper bites are considered “dry bites,” resulting in no toxicity.⁴ Children younger than 6 years are more likely than older children and adults to sustain “dry bites,” although when envenomed, these young children are more likely to have major effects from the envenomation.⁴ Some patients may have a delayed onset of symptoms necessitating an observation period prior to a diagnosis of “dry bite.” If the envenomation is severe, however, swelling and edema may involve the entire extremity within 1 hour. Ecchymosis, hemorrhagic vesicles, and petechiae may appear within several hours (Fig. 134-2).

Systemic signs and symptoms include paresthesias, periorbital fasciculations, weakness, diaphoresis, nausea, dizziness, and a “minty” or metallic taste in the mouth. Severe bites can result in coagulopathies, thrombocytopenia, and a disseminated intravascular coagulation (DIC)-like syndrome called venom-induced consumption coagulopathy.¹⁰ Rapid hypotension and shock, with pulmonary edema and renal and cardiac dysfunction, can also result, particularly if the victim suffers a direct intravascular envenomation. Anaphylaxis has been reported in patients with a previous snake venom exposure; however, anaphylactoid reactions without previous sensitization has also occurred.¹¹

PREHOSPITAL MANAGEMENT

The victim’s extremity should be immobilized and physical activity minimized, with the primary goal of prehospital management being evacuation to a healthcare facility that can deliver antivenom if needed. Certain first aid measures can be dangerous and exacerbate limb morbidity. Incision and suction of the bite wound with the human mouth is contraindicated as it will result in increased tissue damage and poses a high risk of secondary infection. Mechanical suction devices are sold commercially but are not recommended for use. Studies using both animal and human models have found suction devices to be inadequate in venom extraction and possibly contribute to increased local tissue damage.^12,13 Cryotherapy can lead to further wound necrosis and is not currently recommended. Electric shock therapy was historically publicized as a first aid treatment for snakebites, but case reports and animal studies have not documented any improvement with this prehospital technique.^14,15 In fact, the technique suggested by the original case series, in which the authors suggest that “an outboard motor is one commonly available source of such a current,” could lead to increased local tissue and systemic injury. It should also be noted that although routine in other areas of the world, pressure immobilization for North American Crotaline snakebites is not recommended because evidence to demonstrate decreased systemic toxicity is lacking, and there is evidence that suggests increased extremity compartment pressures when it is used.¹⁶