Rattle Snake Envenomation Workup

  • Author: Sean P Bush, MD, FACEP; Chief Editor: Rick Kulkarni, MD   more...
 
Updated: Nov 2, 2010
 

Laboratory Studies

Coagulopathy commonly occurs with rattlesnake envenomation, although clinical bleeding is uncommon.[10, 11, 12, 13] Defibrination and/or thrombocytopenia most often characterize snakebite coagulopathy. Defibrination is manifested by low serum fibrinogen, elevated prothrombin time, and elevated fibrin split products (FSP). Venom-induced thrombocytopenia may exist in association with or independently of defibrination. Abnormal coagulation parameters may last for a week or more. Recurrence of coagulopathy after resolution with antivenom has been reported.

  • Complete blood count (CBC) with differential
  • Platelets
  • Prothrombin time
  • Activated partial thromboplastin time
  • Fibrinogen
  • Type and screen
  • Urinalysis

Rhabdomyolysis may occur from severe envenomation but is best described after canebrake (Crotalus horridus atricaudatus)[14] and Mojave (Crotalus scutulatus)[15] rattlesnake envenomations. Rhabdomyolysis may lead to myoglobinuric renal failure and subsequent electrolyte abnormalities, such as hyperkalemia, hypokalemia, or hypocalcemia.

  • Creatine kinase (CK)
  • Electrolytes
  • Blood urea nitrogen (BUN), creatinine
  • Calcium
  • Phosphorus
  • Urinalysis

For respiratory difficulty, consider arterial blood gases (ABGs), although arterial puncture should be avoided if a severe venom-induced coagulopathy develops.

Obtain laboratory and other diagnostic data on a case-by-case basis. Factors to consider may include severity of envenomation, physician preference, and cost.

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Imaging Studies

Plain radiographs may depict teeth or fangs retained in the wound.

Consider a head CT if the patient has a headache or altered level of consciousness (ALOC) with a severe coagulopathy.

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Other Tests

Obtain an electrocardiogram (ECG), if indicated.

Skin testing is not necessary before administering Crotaline Fab antivenom (CroFab) therapy. Skin testing is described below for educational purposes or for the unusual case in which a practitioner determines it is indicated.[16]

Intracutaneous injection of 0.02-0.03 mL of a 1:10 dilution of horse serum or antivenom is recommended in the Antivenin (Crotalidae) Polyvalent package insert. A positive test result is manifested by the development of a wheal within 5-30 minutes. However, skin testing is very unreliable. False-positive and false-negative test results may occur. Using antivenom (further diluted to 1:100), rather than the horse serum control that is supplied, may increase the sensitivity and specificity of the test.

Skin testing may be considered useful in variably predicting immediate hypersensitivity in cases of moderate envenomation when it is uncertain whether the need for antivenom outweighs the risk of anaphylaxis.

Skin testing may sensitize individuals at risk for future exposures to antivenom, or it may precipitate anaphylaxis.

If antivenom is clearly indicated, it should be started as described below, without waiting to conduct a skin test.

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Procedures

Central venous or interosseous access may need to be obtained. However, avoid placing a central line in a noncompressible site (eg, internal jugular) because of the risk of bleeding from venom-induced coagulopathy.

Fasciotomy may be indicated if measured compartment pressures remain persistently and severely elevated despite adequate antivenom. CroFab has been shown to limit the decrease in perfusion pressure associated with compartment syndrome. Compartment syndrome may manifest subjectively, with complaints of increasing pain, and objectively, with tenderness on passive muscle stretch, a rock hard feel to the compartment or a diminished capillary refill. True compartment syndrome is rare following snakebite, even in patients with severe edema, because most envenomations are believed to be subcutaneous. Myonecrosis has been shown to occur from direct myotoxicity, even after fasciotomy of the affected compartment.

Distinguishing compartment syndrome from the effects of envenomation may be difficult. Similar to compartment syndrome, rattlesnake envenomation may cause a bluish discoloration of the skin or pallor (because of subcutaneous bruising), severe swelling, paresthesias, and pain. If effects are only caused by envenomation and the patient does not have compartment syndrome, capillary refill is normal and compartmental pressure is not elevated.

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Contributor Information and Disclosures
Author

Sean P Bush, MD, FACEP  Professor of Emergency Medicine, Loma Linda University School of Medicine; Consulting Staff, Envenomation Specialist, Department of Emergency Medicine, Loma Linda University Medical Center

Sean P Bush, MD, FACEP is a member of the following medical societies: American College of Emergency Physicians, International Society on Toxicology, Society for Academic Emergency Medicine, and Wilderness Medical Society

Disclosure: Protherics Consulting fee Consulting; Nycomed (formerly Fougera) Grant/research funds Speaking and teaching; Rare Disease Therapeutics Grant/research funds Research; Bioclon Grant/research funds Research

Specialty Editor Board

Robert L Norris, MD  Professor, Department of Surgery, Chief, Division of Emergency Medicine, Stanford University Medical Center

Robert L Norris, MD is a member of the following medical societies: American College of Emergency Physicians, American Medical Association, California Medical Association, International Society of Toxinology, Society for Academic Emergency Medicine, and Wilderness Medical Society

Disclosure: Nothing to disclose.

John T VanDeVoort, PharmD  Regional Director of Pharmacy, Sacred Heart and St Joseph's Hospitals

John T VanDeVoort, PharmD is a member of the following medical societies: American Society of Health-System Pharmacists

Disclosure: Nothing to disclose.

James Steven Walker, DO, MS  Clinical Professor of Surgery, Department of Surgery, University of Oklahoma College of Medicine

James Steven Walker, DO, MS is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American College of Osteopathic Emergency Physicians, and American Osteopathic Association

Disclosure: Nothing to disclose.

John D Halamka, MD, MS  Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center

John D Halamka, MD, MS is a member of the following medical societies: American College of Emergency Physicians, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Chief Editor

Rick Kulkarni, MD  Attending Physician, Department of Emergency Medicine, Cambridge Health Alliance, Division of Emergency Medicine, Harvard Medical School

Rick Kulkarni, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Emergency Physicians, American Medical Association, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine

Disclosure: WebMD Salary Employment

References

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Juvenile southern Pacific rattlesnake (Crotalus oreganus helleri). Photo by Sean Bush, MD.
A recent study suggests that the Extractor (Sawyer Products) does not reduce swelling after rattlesnake envenomation and may be associated with skin necrosis beneath the suction cup. Photo by Sean Bush, MD.
Moderate rattlesnake envenomation in a toddler after treatment with antivenom. Photo by Sean Bush, MD.
 
 
 
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