Snakebite

• • Distinguishing whether the patient has been bitten and envenomed, bitten but not envenomed, or bitten by a nonvenomous snake is critical prior to starting treatments

  • Treatments may not only cause discomfort but may also produce serious side effects

  • Bite by a venomous snake results in envenomation in only 50-70% of cases

  • Degree of envenomation depends on the size of the snake and the duration of contact

Venomous Snakes

• • Indigenous venomous snakes of North America can be placed in 4 groups:

  • 1. Rattlesnake

    2. Copperhead

    3. Cottonmouth

    4. Coral snake

Pit Vipers

• • Include rattlesnakes, copperhead, and cottonmouth

  • Can be distinguished from nonvenomous snakes by a round mouth and a pit between the eyes and the nares on each side

  • Have retractable canaliculated fangs that can rapidly spring into biting position and deliver venom

  • The large venom glands also give the head a triangular or diamond shape

  • Have vertically oriented elliptiform irises

  • Most deliver a primarily hemotoxic venom

  • Hemotoxic effects are mediated by proteolytic enzymes, peptides, and metalloproteins that cause local tissue destruction directly and by intimal injury to blood vessels, followed by thrombosis and necrosis

  • Activation of the coagulation cascade can occur at multiple points, resulting in net anticoagulation

Coral Snakes

• • Have small mouths, short teeth, and deliver secreted venom into prey through created lacerations

  • Bite lacks the characteristic fang marks of bites by pit vipers, sometimes making it hard to detect

  • Body coloration pattern is red bands immediately adjacent to yellow bands

  • Coral snake venom is primarily neurotoxic

  • Neurotoxic venom can cause dysphagia, dysphonia, diplopia, headache, weakness, and respiratory distress

Nonvenomous Snakes

• • Most snakebites in the United States are from nonvenomous snakes

  • Nonpoisonous snakes such as the red milk snake and the scarlet king snake mimic the bright red, yellow, and black coloration of the coral snake

  • -True coral snakes have red bands immediately adjacent to yellow bands

    -The mimics have black bands immediately adjacent to the red bands, thus the mnemonic: "Red on black, venom lack; red on yellow, kill a fellow"

Epidemiology

• • About 8000 people are bitten by venomous snakes in the United States each year

  • Death from serious envenomation occurs in 9-15 victims per year in the United States

Symptoms and Signs

• • Puncture marks, local ecchymosis and discoloration, vesicles and bullae, and rapid appearance of swelling and edema at the injured area

  • Pain of the bite can be quite severe

  • Additional signs of hypotension, diaphoresis, nausea, weakness, and faintness are common

  • Perioral or peripheral paresthesias, taste changes, and fasciculations

  • Signs suggestive of neurotoxic envenomation include dysphagia, dysphonia, diplopia, headache, weakness, and respiratory distress