Prognosis and Grading Severity of Envenomation

The symptoms, signs, and prognosis of envenomation are dependent on a number of factors, including species and size of the snake, nature of the bite (location, number of bites, character of clothing between fangs and skin,

Table 32.3. Snake venom properties.

Local tissue damage (necrotoxins)

Coagulation defects (hemotoxins)

Hemolysis Neurotoxins

Myotoxins Nephrotoxins

Proteases and small peptides damage the epithelial cells and basement membranes of capillaries, altering blood vessel permeability, which leads to loss of blood and plasma into tissues, which causes edema, shock from fluid shifts

Capillary damage and DIC-like state lead to decreased platelets and fibrinogen, hemorrhage, and sometimes shock; not seen with elapid venom Phospholipases induce red cells to swell, causing hemolytic anemia, hemoglobinuria Major components in Mojave rattlesnake and elapid venom, can cause flaccid paralysis of skeletal muscle by blocking transmission at the neuromuscular junction, lead to death by respiratory paralysis Can result in massive skeletal muscle breakdown, myoglobinuria, potential renal failure Cause primary and secondary damage to kidneys

Source: Data from White (6), Iyaniwura (7), Kitchens (23), Wingert (27), and Iyaniwura (36).

Table 32.4. Grade of envenomation.

Severity Type of signs or symptoms

Grade 0 (no envenomation) ■ fang marks, minimal pain and erythema but no local swelling or hemorrhage no systemic symptoms; normal coagulation and no bleeding fang marks with swelling (1-5 inches), moderate pain, and ecchymosis no systemic symptoms; normal coagulation and no bleeding swelling (6-12 inches), pain and ecchymosis progressing rapidly beyond the site of the bite (such as elbow or knee) decreased fibrinogen and/or platelets, but without clinical bleeding (may have minor hematuria, nosebleed) nausea, vomiting, oral paresthesias, unusual tastes, weakness, mild hypotension, mild tachycardia swelling (>12 inches), pain and ecchymosis involving more than an entire extremity or threatening the airway abnormal coagulation measures with hemorrhage altered mental status, falling blood pressure, severe tachycardia, tachypnea, or respiratory insufficiency seen with bite by a large or highly toxic snake (e.g., C. atrox), or multiple bites

Grade IV (very severe) ■ seen with bite of large rattlesnakes (eastern and western diamondback rattlers, timber rattler)

■ sudden pain and rapid local swelling that spreads proximally and may involve the ipsilateral trunk; ecchymoses follow rapidly; bleb formation with spontaneous rupture; areas of necrosis

■ rapid onset of weakness, vertigo, numbness, fasciculation, painful muscular cramping, and tingling about the face (particularly lips); shock may be apparent within a few minutes; nausea and vomiting often appear in the first 10 to 15 minutes; may lead to kidney shutdown, hepatic and cardiovascular damage; coma and death can occur within 30 minutes.

Source: Data from Kunkel et al. (9), Dart et al. (22), Parrish (25), Wingert (27,28), McCollough (32), Lawrence et al. (37), and Scharman and Noffsinger (38).

amount of venom injected), victim's age, size and sensitivity to venom, and subsequent medical care (26,27,32).

There is a fairly uniform system of grading envenomation that has evolved over the past 4 decades. It ranges from no envenomation to very severe, based on such factors as spread of edema, systemic signs (nausea, vomiting, hypotension, tachycardia), and coagulation status (Table 32.4) (9,22,25,27,28,32,37,38).

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