August 2011

Snake Attack

By: Dustin Weaver DVM

A 4yr old female spayed Chocolate Labrador Retriever was presented to the San Juan Veterinary Hospital on emergency. One hour prior the dog was west of Bayfield on a hike with her owners and sustained a rattle snake bite on her fron foot. The patient was driven to Pagosa and was immediately admitted. She was found to be in a state of shock-a very high respiratory rate with weak and rapid pulse. Her pupils were dilated and changing in size. The affected leg was edematous, painful, and swollen. The bite puncture wounds were easily identified. The owners, being in the medical profession, had access to predinose and administered 20mg orally prior to admittance. Other than the aforementioned medication the patient was not taking medication and did not have any preexisting conditions.

Copperhead bites are the most common snake bite reported in the U.S. but rattle snake bites are the deadliest. Although infrequent in the Pagosa area, rattle snake bites are both the most common and most deadly snake bite. This summer the San Juan Veterinary Hospital treated 2 rattle snake attacks. Rattle snakes are grouped with other poisonous snakes called pit vipers (Crotalid spp.). They have heat seeking sensors between the nose and eyes, retractable venom releasing fangs, and a triangular shaped head. The venom is released when they contract their facial musculature from a modified salivary gland. It is not surprising that our victims present with tissue swelling, obtundation, inability to move, seizures, bleeding, and hempdynamic.

Two types of antivenin are available for use in the United States for pit vipers but both are expensive ($500 per dose and most require multiple doses). The antivenin should be administered within two hours of the bite. Antivenin can and has intensified the problem should the patient react to the proteins in it. It becomes more important to use antivenin in cases where the patient is bitten on the face or in a state of shock. Unfortunately, due to the infrequent number of attacks and cost no veterinary clinic in this area carries antivenin. However, for the large majority of cases it is not needed.

The cornerstone of therapy for snake attacks is treating the shock with fluid therapy. Our chocolate lab was given an IV catheter and an initial shock fluid bolus. This improved her pulse quality and rate. Pain was treated with a constant rate infusion of fentanyl. Often in emergency medicine initial stabilization must precede further diagnostic work up. Following stabilization, blood was collected and a blood smear was performed. The effects of the venom will alter the surface of the red blood cells. Unfortunately this abnormality was confirmed in our patient. More blood was saved for a coagulation analysis if needed. Steriod therapy is controversial in the treatment of snake bites. It will counteract some of the toxic effects of the venom, decrease swelling, and decrease the patient's response to the venom. But it may also delay healing and predispose the patient to secondary infections. In our patient steriods were administered prior to presentation and so it was decided that steriod therapy would be continued.

Our patient was hospitalized for three days and the swelling was controlled well with steriod therapy. Her pulse quality and respiratory rate continued to improve and she was taken off of fluid support. To control for secondary infection she was started on IV antibiotics. She was discharged and is doing well, and using the leg. Her owners told us that she no longer enjoys walking in tall grass!


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