injuries poisoning
Snakebites
Diagnosis of Snakebites
Identification of the snake Grading severity of envenomation Definitive diagnosis of a snakebite is aided by positive identification of the snake and clinical manifestations of envenomation. History should include the time of bite, description of the snake, type of field therapy, underlying medical conditions, allergy to horse or sheep products, and history of previous venomous snakebites and therapy. A complete physical examination should be done. A marker should be used to indicate the leading edge of edema on the affected limb or area, and the time the mark was made should be recorded. Snakebites should be assumed to be venomous until proved otherwise by clear identification of the species or by a period of observation. Patients often cannot recall details of the snake’s appearance. Pit vipers and nonvenomous snakes can be distinguished by some physical features (see figure Identifying pit vipers ). Consultation with a zoo, an aquarium, or a poison center (1-800-222-1222) can help in the identification of snake species. Pit vipers have the following features, which help differentiate them from nonvenomous snakes: Arrowhead-shaped (triangular) heads Elliptical pupils Heat-sensing pits between the eyes and nose Retractable fangs A single row of subcaudal plates extending from the anal plate on the underside of the tail Coral snakes in the US have round pupils and black snouts but lack facial pits. They have blunt or cigar-shaped heads and alternating bands of red, yellow (cream), and black, often causing them to be mistaken for the common nonvenomous scarlet king snake, which has alternating bands of red, black, and yellow. The distinguishing feature in the coral snake is that the red bands are adjacent to only yellow bands, not black bands (“red on yellow, kill a fellow; red on black, venom lack”). Coral snakes have short, fixed fangs and inject venom through successive chewing movements. Fang marks are suggestive but not conclusive; rattlesnakes may leave single or double fang marks or other teeth marks, whereas bites by nonvenomous snakes usually leave multiple superficial teeth marks. However, the number of teeth marks and bite sites may vary because snakes may strike and bite multiple times. A dry pit viper bite is diagnosed when no symptoms or signs of envenomation appear within 8 hours after the bite. Severity of envenomation depends on the following: Size and species of the snake (rattlesnakes>cottonmouths>copperheads) Amount of venom injected per bite (cannot be determined by history) Number of bites Location and depth of the bite (eg, envenomation in bites to the head and trunk tends to be more severe than in bites to the extremities) Age, size, and health of the patient Time elapsed before treatment Patient’s susceptibility (response) to the venom Severity of envenomation can be graded as minimal, moderate, or severe based on local findings, systemic symptoms and signs, coagulation parameters, and laboratory results (see table). Grading should be determined by the most severe symptom, sign, or laboratory finding. Envenomation may progress rapidly from minimal to severe and must be reassessed continually. If systemic symptoms begin immediately, Anaphylaxis should be assumed. 