Snakebite envenomation is a complex poisoning because of the combination of the effects of venoms and the human and snake variables that influence venom toxicity Venoms are mixtures of potent enzymes, primarily proteinases, and low– molecular-weight peptides that possess extensive pathophysiologic properties A crotalid venom often has a combination of necrotizing, hemotoxic, neurotoxic, nephrotoxic, and cardiotoxic substances Many venoms induce increased endothelial permeability and venous pooling, creating intravascular depletion A transient hemoconcentration may be present during this plasma “leak.” Hemotoxic effects induce hemolysis, fibrinogen proteolysis, and thrombocytopenia, which along with activation of plasminogen, can lead to a bleeding diathesis in severe envenomation Respiratory failure may occur because of pulmonary edema or a shock state Human factors that influence toxicity to snakebites include the victim’s size and general health and wound characteristics A small child is more susceptible to a given volume of venom than a larger person and unfortunately, young children are commonly bitten more than once Fang penetration of a vessel or subfascial compartment ensures a more rapid absorption and serious systemic effects Likewise, a bite on the head, neck, or trunk hastens systemic absorption FIGURE 90.21 Coral snake Snake variables include the snake’s size, the amount of venom injected, and the potency of the particular species’ venom Conditions that facilitate venom secretion (e.g., long, healthy fangs or full stores of venom) add to the toxicity of the bite An angered and hungry rattlesnake unloads more venom than a recently satiated and surprised rattlesnake It is important for the emergency provider to be aware that coral snake venom may be absorbed without a bite through routes such as the ocular mucous membranes, which can lead to severe neurotoxicity Since the FDA-approved coral snake antivenin is in limited supply, clinicians should consider non–FDA-approved alternative antivenins as well as adjunctive pharmacologic treatments such as neostigmine, under the guidance of a toxicologist Clinical Recognition Generally, it is useful to have a photograph of the snake responsible for the attack when possible, since it can be shared with an expert and used for identification and further management Pit viper A Crotalus envenomation causes intense local pain and burning within a couple of minutes Victims of a significant rattlesnake bite often complain within minutes of perioral numbness, extending to the scalp and periphery, with a metallic taste in the mouth Local ecchymoses and vesicles usually appear within the first few hours, and hemorrhagic blebs are often present by 24 hours Lymphadenitis and lymph node enlargement may also become apparent Without appropriate therapy, there may be progression to necrosis that may extend throughout the bitten extremity Secondary infection is a risk as the snake’s oral flora includes gram-negative bacteria Table 90.22 summarizes local characteristics of pit viper bites Patients may have nausea, vomiting, weakness, chills, sweating, syncope, and other more ominous symptoms of systemic venom absorption such as bleeding, angioedema, and hypotension A copperhead or pygmy rattlesnake envenomation produces fewer local symptoms, and systemic consequences are often minimal or nonexistent unless a small child, multiple bites, or larger than average snake is involved The water moccasin’s effects are more variable There is a relative lack of serious pain or swelling with the Mojave rattlesnake bite, although, as in other Crotalus bites, the patient may complain of paresthesia in the affected extremity Within several hours, these patients may develop neuromuscular symptoms such as diplopia, difficulty in swallowing, lethargy, nausea, and progressive weakness from the large dose of neurotoxin delivered by this species TABLE 90.22 LOCAL SIGNS OF CROTALID (PIT VIPER) ENVENOMATION Pain Edema Vesicles Hemorrhagic blebs Erythema Ecchymosis Necrosis TABLE 90.23 SYSTEMIC SIGNS AND SYMPTOMS OF CROTALID (PIT VIPER) ENVENOMATION General Anxiety, diaphoresis, pallor, unresponsiveness Cardiovascular Tachycardia, decreased capillary perfusion, hypotension, shock Pulmonary Pulmonary edema, respiratory failure Renal Oliguria, hemoglobinuria, hematuria Neuromuscular Fasciculations, weakness, paralysis, convulsions Hematologic Bleeding diathesis The wound should be inspected for fang punctures, and if two are present, the distance between them should be noted An interfang distance of less than mm suggests a small snake; to 12 mm, a medium snake; and more than 12 mm, a larger snake Fang wounds by small snakes such as the pygmy rattler may be extremely subtle; in larger crotalid snakebites, the fang marks may be hidden within hemorrhagic blebs and edema Occasionally, only one puncture or two scratches will be present, but both wounds may be potentially venomous Up to 20% of known rattlesnake strikes not inject venom Other causes of puncture wounds such as rat bites and thorn wounds must also be kept in mind ... rattlesnake unloads more venom than a recently satiated and surprised rattlesnake It is important for the emergency provider to be aware that coral snake venom may be absorbed without a bite through routes