Answers and Discussion

Case #2-- Rattlesnake Bite

Answers and Discussions to the Questions:

• List some differential diagnoses for facial swelling in the dog.
  Although there are many causes of facial swelling (abscesses, cellulitis, dog bite wounds, salivary cysts, venous thrombosis, etc.), the owner saw "Shone" bitten by a snake which she identified as a rattlesnake after killing it.  Additionally, the time of year (May), the suddenness of the swelling, and the very rapid progession of swelling tends to confirm the suspicion of rattlesnake bite.

• Describe how you can diagnose whether or not "Shone" was envenomated by a rattlesnake.

The presence of bite wounds on the dorsum of the head suggests envenomation but there are reports of "dry bites" (no venom in injected).  If you will collect a small amount of peripheral blood place it on a slide with a drop of saline, and then place a coverslip over the blood/saline, you may examine the sample for the presence of "Type III echinocytes".  This appears to be an extremely accurate means of determining rattlesnake envenomation.



Click here to see an enlargement of these stained echinocytes

• If "Shone's" owner had called and asked you whether he should apply ice packs, apply a tourniquet, or suck out the poison, how would you respond to each of these inquires?

Ice and cold-packing of the swelling is contraindicated.  The area around the bite wound is already devoid of normal blood flow and ice will cause further vasoconstriction and potentially lead to necrosis of the skin.

Where would you place the tourniquet...around the neck!!  In general, tourniquets have not been useful in snakebite.  With the tenuous blood supply to the bite area, an incorrectly placed tourniquet may lead to further complications.  By the time the animal reaches your hospital it is unlikely the tourniquet will be useful.

It is unlikely the aspiration of a bite area will significantly affect the outcome of rattlesnake envenomation.  The injected poison is rapidly disseminated into the area and circulation.  One recommendation you can offer animal owners is to immobilize the area and if at all possible, carry the animal instead of allowing her to walk.

• Describe your treatment priorities for "Shone". 
  The treatment priorities in a potential snakebite are as follows:
  
  • Respiration:  With a bite wound on the head or neck area, there is a real potential for occlusion of the airway.  Fortunately this is not common but should it occur, the only recourse would be an immediate tracheostomy.  On admission to the hospital, oxygen administration is useful.
• Shock:  The venom from rattlesnakes contains some very potent vasoactive substances which contribute to shock.  In shock, the priorities are directed to maintaining volume, blood pressure, blood flow, and cardiac function.  Thus, the first treatment is directed to obtaining a vascular access with a large bore intravenous catheter.   Fluid administration is begun with crystalloid fluids at shock volumes (~50 - 60 ml/kg/hour).  Close monitoring is begun to prevent overhydration or excessive hemodilution.
• Treatment of the envenomation.

• Explain your rationale for the administration antivenin.
  Antivenin is useful in rattlesnake envenomation in that it will help alleviate many of the toxic effects of the venom if administered promptly after the snake bite.  Whether it is "required" is very controversial.   It seems unlikely that a single vial of antivenin would be adequate for dogs or cats.  Antecdotal evidence does suggest the morbidity associated with envenomation is reduced with antivenin administration.  Whether this justifies the expense (~$175.00/vial) has yet to be confirmed clinically.  At present, it would seem antivenin is useful but not required for rattlesnake envenomation in Colorado.

• List one reason corticosteroids might be contraindicated following rattlesnake envenomation.

Literature from studies in humans does suggest increased infection rates with corticosteroid administration following rattlesnake envenomation.  Currently, the administration of corticosteroids (dexamethasone-SP) is the standard of care for dogs and cats bitten by a rattlesnake.  

• Indicate whether antihistamines are contraindicated. 
  Again, use of antihistamines is controversial!  Currently, the use of antihistamines are considered standard of care for dogs and cats.  With the cell death which results from envenomation, it seems likely histamine levels would be increased and thus these drugs would be useful.  An additional benefit from the antihistamines is the soporific effect of the drug.  These drugs do not possess analgesic effects and thus use of butorphenol or fentanyl are indicated for relief of pain..

• Predict what you would expect to see from a total platelet count (increased, decreased, or normal).  Disseminated intravascular coagulopathy (DIC) has long been considered a complication of rattlesnake envenomation.  Thus, one would expect the platelet count to be decreased.  In "Shone" the initial platelet count was 40,000/mm3.  However, the activated clotting times were normal and thus no other clotting studies were ordered.  The following day, the platelet count had risen to 165,000/mm3 and "Shone" was discharged from the hospital.

Follow-Up:

        "Shone" was discharged from the Veterinary Teaching Hospital 24-hours after admission.  The swelling of the head had markedly decreased and there were no other signs of adverse responses to the venom.   The day after leaving the hospital, "Shone's" owner called to report he was nervous and panting and did not want to go out to the backyard.  The facial swelling had resolved, his rectal temperature as 101 F and there were no obvious signs of complications.  It was believed that "Shone" was "nervous" about going to the backyard because of his rattlesnake encounter 3 days previously!  No further follow-up was made.

   Shone 24-hours after being bitten by a rattlesnake.

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Copyright Wayne E. Wingfield, Colorado State University, 1998.  All rights reserved.
This page was last updated:  09/04/98