Snakebite Treatment & Management

Updated: May 15, 2017
  • Author: Brian J Daley, MD, MBA, FACS, FCCP, CNSC; Chief Editor: Joe Alcock, MD, MS  more...
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Treatment

Severity of Envenomation

Treatment is based on the severity of envenomation; it is divided into field care and hospital management. See Tables 1 and 2 below.

Table 1. Snakebite Severity Scale (Open Table in a new window)

Criteria Signs/Symptoms Score
Pulmonary    
  No symptom/sign 0
  Dyspnea, minimal chest tightness, mild or vague discomfort, or respirations of 20-25 breaths/min 1
  Moderate respiratory distress (tachypnea, 26-40 breaths/min, accessory muscle use) 2
  Cyanosis, air hunger, extreme tachypnea, or respiratory insufficiency/failure 3
Cardiovascular    
  No symptom/sign 0
  Tachycardia (100-125 beats/min), palpitations, generalized weakness, benign dysrhythmia, or hypertension 1
  Tachycardia (126-175 beats/min) or hypotension with systolic blood pressure < 100 mm Hg 2
  Extreme tachycardia (>175 beats/min) or hypotension with systolic blood pressure < 100 mm Hg, malignant dysrhythmia, or cardiac arrest 3
Local wound No symptom/sign (swelling or erythema < 2.5 cm of fang mark) 0
  Pain, swelling, or ecchymosis within 5-7.5 cm of bite site 1
  Pain, swelling, or ecchymosis involving less than half of the extremity (7.5 cm from site) 2
  Pain, swelling, or ecchymosis extending beyond affected extremity (>100 cm from site) 3
Gastrointestinal    
  No symptom/sign 0
  Pain, tenesmus, or nausea 1
  Vomiting or diarrhea 2
  Repeated vomiting or diarrhea, hematemesis, hematochezia 3
Hematological    
  No symptom/sign 0
  Coagulation parameters slightly abnormal (PTa < 20 seconds, PTTb < 50 seconds, platelets 100,000-150,000/µL, fibrinogen 100-150 mcg/mL) 1
  Coagulation parameters abnormal (PT < 20-50 seconds, PTT < 50-75 seconds, platelets 50,000-100,000/µL, fibrinogen 50-100 mcg/mL) 2
  Coagulation parameters abnormal (PT < 50-100 seconds, PTT < 75-100 seconds, platelets 20,000-50,000/µL, fibrinogen < 50 mcg/mL) 3
  Coagulation parameters markedly abnormal, with serious bleeding or threat of spontaneous bleeding (PT or PTT unmeasurable, platelets < 20,000/µL, fibrinogen undetectable), with severe abnormalities in other laboratory values, including venous clotting time 4
Central nervous system    
  No symptom/sign 0
  Minimal apprehension, headache, weakness, dizziness, chills, or paresthesia 1
  Moderate apprehension, headache, weakness, dizziness, chills, paresthesia, confusion, or fasciculation in area of bite site, ptosis, and dysphagia 2
  Severe confusion, lethargy, seizure, coma, psychosis, or generalized fasciculation 3
  Extremely severe envenomation leading to death 4
a PT = Prothrombin time.



b PTT = Partial thromboplastin time.



Patients are eligible for therapy with CroFab if they have moderate or severe envenomation as described or any degree of envenomation with progression of the envenomation syndrome. Note: As the antivenom dose reflects venom size, not patient size, the US Food and Drug Administration recommends the same initial and subsequent doses for pediatric patients. Data show efficacy and safety for patients as young as 14 months.

Table 2. Severity of Envenomation (Open Table in a new window)

Type of Signs/Symptoms Minimal Moderate Severe
Local Swelling, erythema, or ecchymosis confined to bite site Progression of swelling, erythema, or ecchymosis beyond bite site Rapid swelling, erythema, or ecchymosis involving the entire body part
Systemic No systemic signs or symptoms Non–life-threatening signs or symptoms (nausea/vomiting, mild hypotension, perioral paresthesias, myokymia) Markedly severe signs or symptoms (hypotension [systolic < 80 mm Hg], altered sensorium, tachycardia, tachypnea, and respiratory distress)
Coagulation No coagulation abnormalities or other laboratory abnormalities Mild abnormal coagulation profile without significant bleeding Abnormal coagulation profile with bleeding (INRa, aPTTb, fibrinogen, platelet count < 20,000/µL
Snakebite Severity Score 0-3 4-7 8-20
a INR = International normalized ratio.



b aPTT = Activated partial thromboplastin time.



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General Management Principles

Important considerations when encountering patients with snakebites are described.

Patients with acute presentations require a rapid assessment of the patient's airway. Obstruction or respiratory failure requires the acquisition of a definitive airway, which might require rapid sequence intubation (RSI). Breathing and circulation should also be assessed in the initial state once an airway has been established.

Remove the patient from the snake's territory as soon as stabilization has occurred in order to avoid further harm.

Remove any jewelry or constricting clothing from the patient's affected area. If clothing is not causing any compression or constriction, it can be left alone until the patient is transferred to a hospital for further care.

In the immediate/acute setting, withhold all alcohol and any drugs that may confound clinical assessment or interfere with treatment.

Do not incise the bite site or perform suction. [10]

The most urgent priority, following the initial assessment, is to promptly evacuate the patient to a hospital where antivenin can be given if needed.

A secondary priority is to mark the extent of the redness and swelling with ink, indicating the date and time, so that further progression can be measured.

Further inpatient care

Admission to the hospital is appropriate for most envenomation cases. A "dry bite" without envenomation can occur in a significant percentage of cases (50% in coral snake, 25% from pit viper). Observation in the emergency department for 8-10 hours may be needed for dry bites to ensure lack of progression of symptoms. Patients with severe envenomation need specialized care in the ICU, including provision of blood products, invasive monitoring, and airway protection. Coral snakebites should be observed for a minimum of 24 hours.

Perform serial evaluations for further grading and to rule out compartment syndrome. Depending on clinical scenarios, measure compartment pressures every 30-120 minutes. Fasciotomy can be considered for pressures greater than 30-40 mm Hg. However, fasciotomy has not been shown to improve outcomes, even when compartment pressures are elevated, and is not routinely indicated for crotalid snake envenomation. [11, 12] Antivenin alone has successfully treated documented elevated compartment pressures. [13]

Depending on the clinical severity of the bite, further blood work may be needed, especially clotting studies, platelet count, and fibrinogen level. Late coagulopathy has been reported after using FABAV. F(ab’)2 immunoglobulin derivatives under development have a longer half life than CroFab and have been shown to decrease late coagulopathy after antivenin treatment. [12, 14]

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Prehospital Care

As with all medical emergencies, the goal is to support the patient until arrival at the emergency department. The dictum " primum no nocere " (first, do no harm) has significant meaning here because many poorly substantiated treatments may cause more harm than good, including making an incision over the bite, mouth suctioning, tourniquet use, ice packs, or electric shock.

Appropriate field care should adhere to the basic tenets of emergency life support.

Reassure the patient during the implementation of ABCs.

Monitor vital signs and establish at least one large-bore intravenous line and initiate 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, unless it is necessary to expedite evacuation.

Immediately transfer to definitive care.

Do not give antivenin in the field.

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Emergency Department Care

Physicians who have little experience treating snakebites frequently care for such patients.

Regional centers often have more experience in the care of snakebite victims. Surgical evaluation for an envenomation victim is paramount.

Definitive treatment includes reviewing the ABCs and evaluating the patient for signs of shock (eg, tachypnea, tachycardia, dry pale skin, mental status changes, hypotension).

For victims of pit viper (crotaline snake) bites, evenomation grading determines the need for antivenin. Grades are defined as mild, moderate, or severe. Mild envenomation is characterized by local pain, edema, no signs of systemic toxicity, and normal laboratory 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 laboratory values (eg, decreased hematocrit or platelet count). 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 test results defining consumptive coagulopathy. See Tables 1 and 2 above.

Grading envenomations is a dynamic process. Over several hours, an initially mild syndrome may progress to a moderate or even severe reaction.

For pit viper envenomations, horse-serum antivenin was made available in 1956. The older equine antivenin has been replaced in 2000 by an improved polyvalent antivenin with fewer adverse effects (see Medication). The antigen-binding fragment antivenom (CroFab) is the only FDA-approved snakebite antivenin on the market in the United States. With the reduced adverse-effect profile and demonstrated improvement in tissue injury with antivenin administration, the threshold for dosing is lower. One study from the southwest United States demonstrated a reduction in rate of fasciotomy after more liberal CroFab dosing. [15] In a randomized study of scheduled versus as-needed CroFab dosing in patients whose symptoms were worsening, the Rocky Mountain Poison and Drug Center demonstrated a reduction in pain and other venom effects but noted a 20% acute and 23% delayed drug reaction. [16]

Although copperhead bites are generally self-limiting, morbidity was reduced in moderate envenomation 4 hours after 4 vials of CroFab in 88% of cases. The cases that failed to respond were not changed by further CroFab doses. [17]

CroFab is generally considered safe for children, as many of the studies did not discriminate in age. One large study from Mexico demonstrated no immediate or late allergic reactions to CroFab when administered according to grade of envenomation. [6]

Although CroFab helps control local tissue effects and hemotoxicity, aggressive antivenom therapy does not usually ameliorate neurotoxic effects such as myokymia (spontaneous, fine fascicular contractions of muscle without muscular atrophy or weakness) and major muscle fasciculations. The physician must maintain continuous monitoring of those patients with myokymia, especially of the shoulders, chest, and diaphragm, for the development of respiratory failure and need for mechanical ventilation. [18, 19]

Coral snakes are not pit vipers and their bites should not be treated with CroFab. A previously available Wyeth antivenin for Micruris fulvius is no longer manufactured in the United States. Victims of bites by M fulvius (eastern coral snake) and M tener (Texas coral snake) should receive general wound care and supportive care, including respiratory support in the event of respiratory failure. Poison control and toxicologist consultation should be contacted for suspected coral snake envenomations to obtain the latest location-specific treatment recommendations. See also Coral Snake Envenomation.

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Surgical Care

Surgical assessment focuses on the injury site and concern for the development of compartment syndrome. Fasciotomy is controversial in snakebites and should be considered only for those patients with objective evidence of elevated compartment pressure. If compartment pressures cannot be measured directly, use the physical hallmark of compartment hypertension (pain with passive range of motion), along with distal pallor, paresthesia, or pulselessness for the clinical assessment.

Tissue injury after compartment syndrome is not reversible but is preventable.

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Consultations

Contacting the poison control center is important. Consultation with a surgeon often is warranted in bite management. General and trauma surgeons often have experience with envenomation, resuscitation, complications, and wound care. They can lead the inpatient treatment.

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Complications

Coagulopathy, including delayed coagulopathy, is a frequent complication of pit viper snakebite. Local wound complications may include infection and skin loss.

Cardiovascular complications, hematologic complications, and pulmonary collapse may occur. Neurotoxicity with myokymia of the respiratory muscles may lead to respiratory failure and mechanical ventilation. True compartment syndrome is a rare complication. Death is rare.

Prolonged neuromuscular blockade may occur from coral snake envenomation.

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. Newer studies now report a lower incidence (5.4%) of acute hypersensitivity reactions with CroFab. [20]

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Prevention

Wear protective clothing and never handle snakes.

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