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Snake Envenomation, Moccasins: Differential Diagnoses & Workup
Updated: Jul 24, 2008
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
- Multimedia
Differential Diagnoses
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 Snake Envenomations, Rattle.
- CBC including platelet count
- 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.
Imaging Studies
- Plain radiographs may depict teeth or fangs retained in wound. However, this finding is uncommon; routine radiography is not recommended.
Other Tests
- Skin testing for allergy to antivenom
- Skin testing is not necessary prior to administration of ovine Fab antivenom (CroFab).
- The manufacturer of equine whole IgG antivenom (Antivenin [Crotalidae] Polyvalent) recommends skin testing prior to antivenom administration and provides a vial of horse serum for this purpose. However, experts disagree about whether this test is necessary or helpful.
- If skin testing is to be performed, first prepare for possible allergic reaction. Antihistamines, epinephrine, intubating equipment, and qualified personnel should be present and immediately available when skin testing is performed and when equine antivenom is administered.
- Dilute 0.02-0.03 mL of horse serum or reconstituted equine antivenom in a 1:10 dilution with normal saline. Inject the entire amount (0.2-0.3 mL) subcutaneously.
- A positive test result is manifested by the development of a wheal within 5-30 minutes.
- Skin testing may be considered variably useful in predicting immediate hypersensitivity in cases of moderate envenomation when it is uncertain if the need for antivenom outweighs the risk of anaphylaxis. However, skin testing is unreliable. False-positive and false-negative results may occur.
- If antivenom is clearly indicated, begin administration as described below, without waiting to conduct a skin test.
- Using antivenom rather than the horse serum control that is supplied may increase the sensitivity and specificity of the test.
- Skin testing may sensitize individuals at risk for future exposures to antivenom, or it may precipitate anaphylaxis.
- Electrocardiogram because moccasin venom is not cardiotoxic, routine examination of the electrocardiogram is not required. An ECG may be useful in cases of shock.
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.
More on Snake Envenomation, Moccasins |
| Overview: Snake Envenomation, Moccasins |
 Differential Diagnoses & Workup: Snake Envenomation, Moccasins |
| Treatment & Medication: Snake Envenomation, Moccasins |
| Follow-up: Snake Envenomation, Moccasins |
| Multimedia: Snake Envenomation, Moccasins |
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References
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Further Reading
Keywords
moccasin snake bite , moccasin snake envenomation , pit viper snake bite, moccasin venom, snake bite, Agkistrodon genus, cottonmouth, Agkistrodon piscivorus, copperhead, Agkistrodon contortrix, cantil, Agkistrodon bilineatus, mamushi, Agkistrodon blomhoffii, Siberian pit viper, Agkistrodon halys, Central Asian pit viper, Agkistrodon intermedius, Malayan pit viper, Calloselasma rhodostoma, hundred-pace snake, Deinagkistrodon acutus
