Snake Bites
Snake bite management in the United States
Snake bites account for approximately 125,000 deaths annually worldwide. The venom from four families of snakes (Atractaspididae, Colubridae, Elapidae, and Viperidae) are toxic to humans. Snake bites are more common worldwide than they are in the United States. The principles of management of snake bites outside the United States are discussed separately.
Estimates from the 1960s suggested that there were approximately 8000 bites each year from poisonous snake species in the United States, with 10 to 12 deaths annually Approximately one-half of snake bites occur in children.
Most bites in the United States result from envenomation with snakes of the family Viperidae, subfamily Crotalinae, which includes rattlesnakes and copperheads. A small number of bites are caused by coral snakes and imported exotic snakes.
The appropriate management of snake bites is controversial, and little data exist about the relative efficacy of management strategies. A suggested algorithm for the management of snake bites in the United States is illustrated in the algorithm.
The following general principles are agreed upon:
-- The patient should be removed from the snake's territory, kept warm and at rest, and be reassured.
-- The injured part of the body should be immobilized in a functional position below the level of the heart.
-- The wound should be cleansed.
-- Withhold alcohol and drugs that may confound clinical assessment.
-- Attempt to identify the snake, without endangering the patient or rescuer. A digital photo taken at a safe distance may be useful. Snake parts should not be handled directly. The bite reflex may remain intact in recently killed snakes, possibly being able to inflict a bite
-- Transport the patient to the nearest medical facility as quickly as possible.
Venomous or nonvenomous? — Snake bites should be differentiated from bites from other animals and from lesions induced by sharp objects. Among patients with a snake bite, the following characteristics may help differentiate venomous from nonvenomous snakes
Venomous rattlesnakes have a triangular shaped head and the pupil is elliptical. They also have hollow retractable fangs through which venom is injected into the victim. In contrast, the head of nonvenomous snakes is rounded as is the pupil. They do not have fangs.
Coral snakes have small heads and fangs, but can be identified by their brightly colored bands. They can be differentiated from similar nonvenomous snakes by their banding patterns. Venomous coral snakes within the United States have red and yellow bands adjacent to each other (remembered by the phrase "red and yellow, kill a fellow; red and black, friend of Jack")
Although one survey found that 81 percent of people at a street fair could accurately differentiate venomous from nonvenomous snakes, misidentification (particularly in an emergency situation) may have potentially serious outcomes and patients with possible envenomation should be observed closely
Pressure immobilization — The pressure immobilization technique to delay systemic absorption of snake venom is widely used in Australia where elapid toxin primarily causes neurotoxicity without tissue necrosis. It is usually not advised following bites from snakes with locally necrotic venom, such as vipers present in the United States. However, it may be useful for bites by elapids and when there may be significant delays in transfer to medical facilities.
Methods not recommended — Methods such as incision and oral suction, mechanical suction devices, cryotherapy, surgery, and electric shock therapy have been widely used but are no longer recommended. As an example, a common misconception is that one should apply a tourniquet, suck out the poison, and spit it out. However, this approach is strongly discouraged, since it can damage nerves, tendons, and blood vessels and lead to infection.
Furthermore, venom removal by suction is minimal. This was illustrated in a study of mock venom extraction with a mechanical suction device in human volunteers; suction reduced the total body venom burden by only two percent
HOSPITAL MANAGEMENT — Snake envenomation is a medical emergency that is readily treatable by antivenom. However, approximately 25 percent of bites from venomous snakes do not result in significant envenomation; thus, the principle of primum non nocere ("first, do no harm") applies.
Following clinical assessment and baseline testing, the patient should be closely observed for features of local and systemic toxicity. Should none develop and repeat laboratory tests remain normal after 8 to 12 hours, the patient can be reassured that no significant envenomation has occurred and discharged from acute medical care. A somewhat longer period of observation (minimum of 12 hours) is recommended for suspected coral snake bite, since neurotoxicity may be delayed
Assessing for envenomation — An understanding of the effects of snake venom is important when assessing and treating patients; toxins from snakes can result in…
-- Coagulopathy
-- Rhabdomyolysis
-- Nephrotoxicity
-- An increase in vascular permeability and consequent hypotension
-- Local tissue damage
Neurotoxicity, which can lead to respiratory depression
Following envenomation by snakes of the subfamily Crotalinae, local tissue destruction, coagulopathy, and hypotension are prominent.
The Mojave rattlesnake (Crotalus scutulatus) is the only rattlesnake species associated with significant neurotoxicity, which can produce respiratory depression or respiratory failure.
The Elapidae family of snakes is less common in the United States, but coral snakes are found in a number of regions. Envenomation occurred in 75 percent of patients bitten by Eastern coral snakes (Micrurus fulvius fulvius) in one series and neurotoxicity was common
The initial and subsequent clinical evaluation should be directed at the following features, which should be meticulously documented:
-- Systemic reactions such as nausea, vomiting, abdominal pain, paresthesias, and dizziness.
-- Physical examination findings such as postural hypotension and tachycardia, local oozing or blistering (outlining the extent of tissue involvement with an indelible marker), lymphadenopathy, and local tissue damage, clinically evident signs of bleeding.
-- Laboratory evaluation should include prolonged whole blood clotting time, prothrombin time, partial thromboplastin time and fibrin degradation products, serum creatine kinase, and urinalysis. Other routine tests should be performed as a baseline, such as a complete blood count, blood urea nitrogen, serum creatinine and electrolytes, electrocardiogram and arterial blood gases.
-- For suspected coral snake or Mojave rattlesnake envenomation, serial neurologic examinations should be performed. As mentioned above, neurologic involvement may be delayed up to 12 hours.
COMPLICATIONS AND OUTCOMES OF SNAKE BITES — Compartment syndromes are rare following snake bites, but the clinical appearance may mimic the local pain and swelling following an uncomplicated snake bite. Fasciotomy should only be performed following confirmation of raised intracompartmental pressure (>40 mmHg in adults) by means of a Stryker needle (Stryker Instruments, Kalamazoo, MI) or an intravenous catheter with pressure transducer and the correction of any coagulopathy with antivenom and/or clotting factors.
In the review of 227 patients with rattlesnake bites, of whom 211 received ACP, almost all patients had a favorable outcome. The only death in this series occurred in an 80 year-old man who had a myocardial infarction. One other patient required reconstructive surgery for significant local tissue loss; no fasciotomies were performed. The median duration of admission was one day, and only 10 percent of those admitted required hospitalization for longer than three days.
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