The pit vipers receive their name from the heat-sensing pit between their eyes and their nostril. Other characteristics that distinguish these snakes from the nonvenomous snakes include retractable fangs, a triangular rather than rounded head, an elliptical rather than round pupil, and a single row of scales on the ventral side of the tail. Nonvenomous snakes (as well as coral snakes) have a double row of ventral scales. In addition, rattlesnakes that have undergone at least one skin shedding have one or more rattles at the end of their tails.

Coral snakes can be identified by their red-yellow-black-yellow-red banding pattern, with the bands completely encircling the snake’s body. King snakes and milk snakes (nonvenomous) also have banding patterns similar to the coral snake; however, in the king and milk snakes the pattern is red and yellow bands separated by black bands, thus the phrase “red next to black, friendly to jack, red next to yellow, kill a fellow.”

Pit viper venom is a complex mixture of peptides and enzymes that have the potential to create local tissue injury and necrosis, as well as deleterious effects on the cardiovascular, pulmonary, renal, and neurologic systems (2,4). Severe burning at the site usually develops within minutes of the bite. Swelling and ecchymosis progress to a variable extent away from the injury. Complaints of weakness, a minty or metallic taste, as well as perioral or lingual numbness may be present. Tachycardia, hypotension, and respiratory distress, as well as muscle fasciculations and paresthesias, can occur with a number of pit viper venoms (2).

Coral snake envenomation is usually manifest by its neurotoxic effects, with local swelling being uncommon. Systemic signs may be delayed for up to 12 hours and can then progress rapidly, with the neurotoxic effects being extremely difficult to halt once they begin (5). For this reason, it is recommended that antivenin be given for all suspected coral snake envenomations. The earliest complaints following coral snake envenomation are usually of nausea, vomiting, headache, and abdominal pain. The victim may have marked pallor and diaphoresis. Manifestations of cranial nerve dysfunction, such as difficulty with swallowing, ptosis, and slurred speech, can occur.

Management in the field should focus primarily on transporting the victim as quickly as possible to the nearest hospital and application of a circumferential pressure wrap that obstructs lymphatic but not arterial flow. Additional
measures include calming the victim, keeping the injured body part immobilized in a position at or just below the level of the heart, and the removal of rings, watches, and constricting clothes. Previously recommended therapies such as incision and suction, electric shock, and cryotherapy delay transport and potentially exacerbate the injury (2,4). If edema is present, it is helpful to mark the advancing border of edema every 15 minutes to assist professionals in determining the severity of envenomation. If a transport delay of greater than 60 minutes is anticipated, some experts recommend a constriction wrap placed several inches above the bite. The band should be tight enough to occlude only lymphatic flow (2). The decision to use antivenin is based on clinical and laboratory criteria.

Initial hospital management is directed toward the establishment and maintenance of the airway, breathing, and circulation. Hypotension is aggressively treated with crystalloid solutions. A history should be obtained with emphasis on timing of bite, first aid measures taken, and a description of the snake. Details of the past medical history should include any coexisting medical conditions; allergies, particularly to horse or sheep products; and any history of previous snakebites and details of their treatment. A complete physical examination is performed with special attention to the cardiovascular, pulmonary, and neurologic systems. The bite should be examined for fang marks as well as erythema, edema, ecchymosis, and tenderness. Baseline circumferential measurements at several points proximal to the injury should be documented and repeated every 15 to 20 minutes until progression of swelling ceases or subsides (4). Progressive swelling should be used as a guide for the administration of antivenin. Laboratory studies include a complete blood count, coagulation studies, fibrin degradation products, electrolytes, blood urea nitrogen, serum creatinine, and urinalysis. These studies should be repeated after the administration of antivenin. Tetanus prophylaxis should be administered if indicated. It is recommended that patients without any clinical or laboratory manifestation of envenomation be watched for at least 8 hours because signs and symptoms can be delayed (5). Victims of coral snake bites should be admitted for a minimum of 12 hours. If the snake is confirmed to be a coral snake, antivenin should be administered regardless of the presence or absence of signs or symptoms of envenomation because neurotoxicity can progress rapidly and is difficult to reverse (2).

There are two types of antivenin used in pit viper envenomation. Antivenin (crotalidae) polyvalent (ACP) (Wyeth-Ayerst Laboratories, Philadelphia, PA) is derived from horses immunized with two North American and two South American pit vipers, and can be used for bites by any North American pit viper. As a heterologous serum product, ACP carries the risk of anaphylactic (IgE mediated), anaphylactoid (due to direct complement activation), and delayed serum sickness. The manufacturer recommends a test dose, but many have found the initial skin test to be unreliable in predicting anaphylaxis (2). ACP is still recommended in severe cases of envenomation regardless of a positive skin test. Even with a negative reaction to the skin test, the clinician should have equipment and medication on hand in the event of a severe reaction. It has been reported that the manufacturer has planned to discontinue this antivenin (4).

A newer antivenin, CroFab (Protherics, London), is now available. This antivenin is derived from four groups of sheep, each immunized to the venom of one of four species of pit viper. No skin test is recommended. The initial dose is 4 to 6 vials over 1 hour. The patient is then monitored for an additional hour. If progression of signs and symptoms occur, an additional dose of 4 to 6 vials is administered. This cycle continues until there is stabilization in the signs and symptoms. After initial control is achieved, an additional two vials is given at 6, 12, and 18 hours (4). These additional doses are recommended due to the observation that, in some patients, there was a recurrence of effects of venom after the initial dose, probably related to the rapid renal clearance of the Fab fragment (6,7). Another study reported the recurrence of hypofibrinogenemia 7 days after treatment was completed (8).

A separate antivenin is available for bites of the eastern and Texas coral snake, but not for the Sonoral coral snake. The administration is similar to that of ACP (2). However, more recent reports have stated that Wyeth-Ayerst may also discontinue the manufacturing of this antivenin (4).

The wounds should be cleansed thoroughly and the extremity splinted. Surgical debridement of necrotic tissue may be required, but should be delayed until the wound has stabilized. Pit viper venom has antibacterial activity (9), and many do not recommend prophylactic antibiotics (2). However, if first aid efforts included incision and mouth suction, a broad-spectrum antibiotic such as amoxicillin/clavulanate should be considered (2). Routine fasciotomy is not recommended, but should be based on measured compartment pressures more than 30 mm Hg. In the event of elevated pressures, some authors recommend elevation of the extremity and the administration of an additional four to six vials of CroFab. If these measures fail to reduce the compartment pressure in 3 to 4 hours, fasciotomy is indicated (4).

Envenomation is a complex medical emergency. A regional poison control center should be contacted for assistance
in treating a victim of a native or exotic venomous snake (National Hotline: 800-222-1222). These centers can provide a list of consulting physicians throughout the United States who are experienced in the management and treatment of bites from venomous snakes (4).