PATHOPHYSIOLOGY AND CLINICAL MANIFESTATIONS Crotaline Envenomation

The severity and clinical manifestations of envenomation depend on a number of factors, including number of strikes, depth of envenomation, size of the snake, potency and amount of venom injected, size and underlying health of the victim, and location of the bite. Larger snakes generally inject more venom. Children and small adults, as well as those with underlying medical conditions (diabetes mellitus, cardiovascular disease), may be more seriously affected by envenomation.

Local Reactions

Pit vipers produce a characteristic bite when they strike, and distinct fang marks can usually be identified. Fang marks can be single, double, or, occasionally, multiple.

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FIG. 117-1. Features of pit vipers and harmless snakes. (Modified and reprinted with permission from Parrish HM, Carr CA: Bites by copperheads in the United States. JAMA 1967;201:927.)


Crotaline (pit viper) venom is usually injected only into the subcutaneous tissue, although deeper, intramuscular (subfascial) envenomation does (rarely) occur. Not every bite releases venom; so-called dry bites occur in up to 20% of strikes. Symptoms may range from mild to severe, but the initial benign presentation of a pit viper bite can be very misleading (Table 117-2). Compared with the venom of rattlesnakes, the venom of water moccasins (cotton-mouths) produces less-severe local and systemic pathology, and envenoma-tion from copperheads tends to be less severe than that of either rattlesnakes or water moccasins.

Envenomation is a dynamic and ever-changing process that can rapidly and unpredictably progress to serious local or systemic involvement. It may require a number of hours for the fuU extent of envenomation to become evident. As a general rule, however, it may be assumed that if no symptoms develop within 8-12 hours from the time of the bite, envenomation from a North American pit viper has not occurred (dry bite).

Systemic Signs

When venom is injected subcutaneously, it travels by lymphatic and superficial venous channels and spreads rather slowly to reach the general circulation. It generally requires a number of hours for subcutaneous envenomation to produce systemic symptoms, but this timetable is quite variable. Intravascular en-venomation produces significant systemic symptoms in a matter of minutes. Systemic signs often include nonspecific weakness, malaise, nausea, and restlessness. More severe envenomation produces confusion, abdominal pain, vomiting, diarrhea, sweating, dyspnea, tachycardia, hypotension, blurred vision, salivation, and a metallic taste in the mouth. Rarely, patients may exhibit disseminated intravascular coagulation (DIC) with spontaneous bleeding, along with significant hypotension and multiorgan system failure. Although local tissue destruction dominates most crotaline envenomations, neurotoxic effects occur with the Mojave rattlesnake (Crotalus scutulatus scutulatus).

Hematologic

Significant crotaline envenomation may produce complex and dramatic hematologic abnormalities secondary to the effects of the venom on the blood coagulation pathways, endothelial cells, and platelets. Fibrinogen concentrations drop and the platelet count falls. The prothrombin time (PT) and partial thromboplastin time (PTT) are prolonged and frequently unmeasurable.

Anaphylaxis

Rarely, a patient bitten by a crotaline may experience anaphylaxis from the venom itself. This can complicate evaluation or mimic a severe systemic reaction to venom. The presence of pruritus and urticaria or wheezing, which is uncommon with envenomation, suggests anaphylaxis. The symptoms respond to standard treatment for anaphylaxis (epinephrine, antihistamines, and corticosteroids).

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