Moccasin Envenomation Workup

Updated: Aug 10, 2016
  • Author: Sean P Bush, MD, FACEP; Chief Editor: Joe Alcock, MD, MS  more...
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Workup

Laboratory Studies

Coagulopathy and thrombocytopenia may occur with pit viper envenomation. However, these problems are much less common after moccasin envenomations than after rattlesnake envenomations. Numeric coagulopathy and/or thrombocytopenia occur in approximately 10% of copperhead envenomations; clinically significant bleeding occurs in less than 5%. For a more detailed discussion of coagulopathy induced by pit viper venom, see Rattlesnake Envenomation. Perform the following laboratory tests:

  • CBC count including platelet count
  • Prothrombin time/international normalized ratio (PT/INR)
  • Activated partial thromboplastin time (aPTT)
  • Fibrinogen
  • Type and screen, only if severe coagulopathy/thrombocytopenia are present or clinical bleeding is suspected

Additional laboratory and other diagnostic data should be obtained on a case-by-case basis. Factors to consider may include severity of envenomation, physician preference, and cost. Bacterial cultures are rarely helpful. The incidence of infection in these envenomations is approximately 2%. Patients who develop shock, respiratory failure, or signs suggesting rhabdomyolysis may benefit from measurements of electrolytes, BUN, creatinine, creatine phosphokinase (CPK), and arterial blood gases, on a case-by-case basis.

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Imaging Studies

Plain radiographs may depict teeth or fangs retained in wound. However, this finding is uncommon; routine radiography is not recommended.

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Other Tests

Skin testing for allergy to antivenom: Skin testing is not necessary prior to administration of ovine Fab antivenom (CroFab).

Because moccasin venom is not cardiotoxic, routine examination with electrocardiography is not required. An ECG may be useful in cases of shock.

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Procedures

Fasciotomy is rarely indicated in cases of moccasin envenomation.

Because envenomation produces limb swelling, severe pain, and pain with passive stretch, it is common for envenomated limbs to appear similar to limbs with compartment syndrome. However, true compartment syndrome is present in less than 2% of moccasin envenomations.

Compartment pressure monitoring is indicated in cases of suspected compartment syndrome.

The preferred therapy for compartment syndrome due to moccasin envenomation is administration of antivenom. Crotaline Fab antivenom has been shown to improve perfusion pressures in an animal model and in human case reports.

Fasciotomy should be reserved for cases in which compartment pressures remain elevated despite administration of adequate doses of antivenom, or in cases of compartment syndrome when antivenom cannot be obtained.

Because tissue pressures in the fingers and toes cannot be measured accurately, the diagnosis of suspected compartment syndrome in the digits is difficult. If capillary refill is poor, administer antivenom to reduce swelling and attempt to restore perfusion. If capillary refill remains poor after administration of adequate doses of antivenom, digit dermotomy may be indicated.

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