Types of Snakes:

Elapidae includes the coral snakes (Micrurus fulvius fulvius and Micrurus fulvius tenere). The eastern and western species that inhabit the United States are brightly colored with red, yellow, and black rings. The nonvenomous king snakes share the same colors but not in the same order. A common warning is "red on yellow, kill a fellow; red on black, venom lack." Coral snake pupils are round, and their subcaudal scales are arranged in double rows. The southern and southwestern states provide the dry sandy conditions (and often a body of water) that coral snakes prefer.

Cobras, mambas, and kraits also are also members of the family elapidae but are not indigenous to the Americas. However, an increasing number of exotic species are kept by both zoos and private collectors making bites by non- indigenous species increasingly common.

Pathophysiology:

Coral snakes have shorter fangs and smaller mouths. This allows them less opportunity for envenomation than the crotalids, and their bites more closely resemble chewing rather than the strike for which the pit vipers are famous. Both methods inject venom into the victim to immobilize it quickly and begin digestion.

Venom is mostly water. Enzymatic proteins in venom impart its destructive properties. Proteases, collagenase, and arginine ester hydrolase have been identified in pit viper venom. Neurotoxins comprise the majority of coral snake venom. Enzyme concentrations vary among species, thereby causing dissimilar envenomations. Copperhead bites generally are limited to local tissue destruction. Rattlesnakes can leave impressive wounds and cause systemic toxicity. Coral snakes may leave small wounds that later result in respiratory failure from the typical systemic neuromuscular blockade.

The local effects of venom serve as a reminder of the potential systemic disruption of organ system function. One effect is local bleeding; coagulopathies are not uncommon with severe envenomations. Another effect, local edema, increases capillary leak and interstitial fluid in the lungs. Pulmonary mechanics may be altered significantly. The final effect, local cell death, increases lactic acid concentration secondary to changes in volume status and requires increased minute ventilation. The effects of neuromuscular blockade result in poor diaphragmatic excursion. Cardiac failure can result from hypotension and acidosis. Myonecrosis raises concerns about myoglobinuria and renal damage.

Frequency/Mortality/Morbidity:

A 20-year review of data from the National Vital Statistics Systems identified 97 fatalities. The state of Texas had the most fatalities (17), followed by Florida (14), and Georgia (12). Deaths secondary to snake bites are rare. With the proper use of antivenin, they are becoming rarer still. The national average has been less than 4 deaths per year for the last several years. Local tissue destruction rarely contributes to long-term morbidity. Occasionally, skin grafting is required to close a defect from fasciotomy, but wounds requiring fasciotomy to reduce compartment pressures from muscle edema are infrequent. Data gathered in a 5-year retrospective chart review from the University of Tennessee Medical Center at Knoxville (UTMCK), a level-I trauma center, focused on 25 bites. Of these, 4 required fasciotomy and 2 subsequently needed split-thickness skin grafting. The average length of stay was 3.2 days. No deaths occurred, and morbidity was limited to the local wounds.

History/Physical:

It is important to inquire about the time the bite occurred and details about the onset of pain. Early and intense pain implies significant envenomation. Local swelling, pain, and paresthesias may be present. Systemic symptoms include nausea, syncope, and difficulty swallowing or breathing. Paresthesias and dysthesias forewarn neuromuscular blockade and respiratory distress (more common with coral snakes).

The following established routine should be followed for a complete comprehensive examination:

• 1) Vital signs, airway, breathing, circulation,
• 2) Fang marks or scratches (determine coral snake bite pattern by expressing blood from the suspected wound),
• 3) Local tissue destruction,
• 4) Soft pitting edema that generally develops over 6-12 hours but may start within 5 minutes,
• 5) Finally, examine for bullae, streaking, erythema, contusions, systemic toxicity, hypotension, petechiae, epistaxis, and hemoptysis.

Lab Studies/Imaging Studies/Other Tests:

Imaging studies are done on an as-needed basis and includes: Baseline chest radiograph in patients with pulmonary edema, and plain radiograph to rule out retained fang(s). Compartmental pressures may need to be measured. Measurement of compartmental pressures is indicated when significant swelling is present, pain is out of proportion to exam, and if paresthesias are present in the affected limb.

Medical Care:

As with all medical emergencies, the goal is to support patients until they arrive at the emergency department. The phrase "first, do no harm" has significant meaning here because many poorly substantiated treatment plans may do more harm than good, including making an incision over the bite, mouth suctioning, tourniquets, ice packs, or electric shock. Appropriate field care should adhere to the basic tenants of emergency life support. Reassure the patient to preclude hysteria during the implementation of ABCs. Monitor vital signs and establish at least 1 large bore intravenous and crystalloid infusion. Administer oxygen therapy. Keep a close watch on the airway at all times in case intubation becomes necessary. Restrict activity and immobilize the affected area (commonly an extremity); keep walking to a minimum. Negative-pressure suctioning devices offer some benefit if used within several minutes of envenomation. Again, do not make an incision in the field. Immediately transfer to definitive care. Do not give antivenin in the field.

When the patient arrives to the hospital, the emergency physician should call the poison control center and contact the general surgeon on-call. Surgical evaluation for envenomation is paramount. Definitive immediate treatment includes reviewing the ABCs and evaluating the patient for signs of shock (eg, tachypnea, tachycardia, dry pale skin, mental status changes, hypotension). Envenomation grading determines the need for antivenin in pit viper victims. Grades are defined as mild, moderate, or severe. Mild envenomation is characterized by local pain, edema, no signs of systemic toxicity, and normal lab values. Moderate envenomation is characterized by severe local pain; edema larger than 12 inches surrounding the wound; and systemic toxicity including nausea, vomiting, and alterations in lab values (eg, fallen hematocrit or platelet values). Severe envenomation is characterized by generalized petechiae, ecchymosis, blood- tinged sputum, hypotension, hypoperfusion, renal dysfunction, changes in prothrombin time and activated partial thromboplastin time, and other abnormal tests defining consumptive coagulopathy. Grading envenomations is a dynamic process. Over several hours, an initially mild syndrome may progress to a moderate or even severe reaction.

Antivenin should be given for coral snake bites as a standard of care if the patient presents within 12 hours of the bite, regardless of local or systemic signs. Neurotoxicity may develop without warning and lead to respiratory failure.

Surgical Care:

Complications:

Antivenin-associated complications include immediate (anaphylaxis, type I) and delayed (serum sickness, type III) hypersensitivity reactions. Anaphylaxis is an event mediated by immunoglobulin E (IgE), involving degranulation of mast cells that can result in laryngospasm, vasodilatation, and leaky capillaries. Death is common without pharmacological intervention.

Serum sickness occurs 1-2 weeks after administering antivenin. Precipitation of antigen-immunoglobulin G (IgG) complexes in the skin, joints, and kidneys is responsible for the arthralgias, urticaria, and glomerulonephritis (rarely). Usually more than 8 vials of antivenin must be given to produce this syndrome. Supportive care consists of antihistamines and steroids.

Medical/Legal Concerns: