This chapter outlines general principles for the evaluation and management of victims of envenomation and poisoning by venomous snakes and marine creatures. Because the incidence of serious bites and stings is relatively low in developed nations, there is a paucity of relevant clinical research; as a result, therapeutic decision-making often is based on anecdotal information.
Venomous snakes belong to the families Viperidae (subfamily Viperinae: Old World vipers; subfamily Crotalinae: New World and Asian pit vipers), Elapidae (including cobras, kraits, coral snakes, and all Australian venomous snakes), Hydrophiidae (sea snakes), Atractaspididae (burrowing asps), and Colubridae (a large family in which most species are nonvenomous and only a few are dangerously toxic to humans). Bite rates are highest in temperate and tropical regions where populations subsist by manual agriculture. Recent estimates indicate somewhere between 1.2 million and 5.5 million snakebites worldwide each year, with 421,000–1,841,000 envenomations and 20,000–94,000 deaths. Such wide-ranging estimates bear testimony to two facts: collection of data is problematic in the regions most affected by venomous snakes (the "developing world"), and what constitutes a "snakebite" varies among researchers. Some count all snakebites (a figure that may include bites by nonvenomous snakes), whereas others count only apparent envenomations.
The typical snake-venom apparatus consists of bilateral venom glands situated below and behind the eye and connected by ducts to hollow anterior maxillary teeth. In viperids (vipers and pit vipers), those teeth are long mobile fangs that retract against the roof of the mouth when the animal is at rest. In elapids and sea snakes, the fangs are smaller and are relatively fixed in an erect position. In ∼20% of pit viper bites and higher percentages of other snakebites (up to 75% for sea snakes), no venom is released ("dry" bites). Significant envenomation probably occurs in ∼50% of all venomous snakebites.
Differentiation of venomous from nonvenomous snake species can be difficult. Viperids are characterized by somewhat triangular heads (a feature shared with many harmless snakes), elliptical pupils (also seen in some nonvenomous snakes, such as boas and pythons), enlarged maxillary fangs, and, in pit vipers, paired heat-sensing pits (foveal organs) on each side of the head. The New World rattlesnakes generally have a series of interlocking keratin plates (the rattle) on the tip of the tail; this rattle is used to dissuade potential threats. Color pattern is notoriously misleading in identifying most venomous snakes. Many harmless snakes have color patterns that closely mimic those of venomous snakes found in the same region.
Venoms and Clinical Manifestations
Snake venoms are complex mixtures of enzymes, low-molecular-weight polypeptides, glycoproteins, metal ions, and other constituents. Among the deleterious components are hemorrhagins that promote vascular leakage and cause both local and systemic bleeding. Proteolytic enzymes cause local tissue necrosis, affect the coagulation pathway at various steps, and impair organ function. Myocardial depressant factors reduce cardiac output, and ...