Hemostatic aspects of envenomation by North American snakes.

1. North American poisonous snakes have a wide spectrum of complex venoms. 2. Venom, especially that of the rattlesnakes, may cause a variety of hemostatic abnormalities by directly, yet only partially, cleaving fibrinogen, activating the fibrinolytic system, or activating and clearing platelets through the action of proteolytic enzymes. 3. Because these venoms do not result in the generation of thrombin, the syndrome is distinct from true DIC. Bleeding or thrombosis is rare. 4. As thrombin generation remains intact, hemostasis is largely preserved despite dramatic changes in hemostatic tests. 5. Therapy with heparin, blood, or blood products is rarely indicated. 6. Therapy with antivenin in selected cases is logical and efficacious.