Supportive Care for Venomous Snake Bites

Coordinate urgent MEDEVAC directly to appropriate medical facilities where antivenom is stored, if it is known that those products can be used in MWDs.

Hospitalize any MWD with history or signs suggesting envenomation for at least 24-48 hours to monitor progression.

Ensure patent airway, provide supplemental oxygen, and ventilation, as needed. Remove any canine equipment that may become restrictive due to local tissue swelling.

Place an IV catheter.

DIAGNOSTICS

Obtain initial vital signs measurements including a blood pressure to assess for hypotensive shock.

Perform a CBC, blood chemistry panel, and urinalysis. Do not perform a cystocentesis due to risk of coagulopathy.

If possible, perform a PT/aPTT or ACT. Coagulation machines meant for human blood are not reliable for canine coagulation parameters.

Examine a blood smear to evaluate for echinocytosis and perform a manual platelet count.

TREATMENT

Antivenom

Antivenom choice should be determined by the MWD’s geographical area and suspected species of snake involved. Many antivenom products, included recently developed polyvalent antivenoms, such as POLYSERP™ have not been tested or approved for use in dogs.

Dose based on the severity of envenomation and clinical response to antivenom therapy.

Follow manufacturer directions for reconstitution (if applicable), dilution, and administration if antivenom is clinically indicated and available.

Monitor for hypersensitivity reactions.

Analgesia

Fully reversible opioids preferred until patient is no longer a risk for hypotension. (See Analgesia and Anesthesia K9 CPG).

NOTE: Do not treat with NSAIDs, given the propensity for envenomated dogs to develop coagulopathies and secondary acute kidney injuries.

Administer isotonic crystalloids at a rate based on clinical signs and laboratory findings. A fluid rate of 1.5 – 2 times maintenance is often an appropriate initial starting point; however, fluid boluses may initially be necessary. General maintenance fluid rate is 40-60 mL/kg/day. Adjustment to fluid rate is based on patient’s clinical response, monitoring ins and outs and clinical parameters such as body weight, CBC and chemistry values. Monitor for signs of fluid overload such as increasing body weight (>10%), tissue edema, serous nasal discharge, or increased respiratory rate or effort.

Manage any open wounds that develop. (See K9 Wound Management CPG)

Do NOT use tourniquets, ice packs, heating, or local vasoconstriction (e.g., injection of epinephrine locally) in an attempt to slow venom spread.

Confine MWDs to minimize venom distribution.

MONITORING

Snakebite Severity Score (SSS) should be considered as an objective tool to guide antivenom administration. A SSS assigns a score of 0-3 or 0-4 for six body areas to assess neurological, gastrointestinal, cardiac, coagulation, local wound, and pulmonary parameters.10 A score of 20 is consistent with severe envenomation. SSS is most helpful for monitoring trends and can be misleading in the subacute setting as signs can be delayed.11 Consider completing a SSS every six hours during patient hospitalization. (See Table 1.)

Repeat diagnostics as necessary (to include PCV/TS, blood chemistry panel, platelet count, blood pressure) 4-6 hours after initial baseline, as needed based on clinical signs, and at time of discharge.

Measure and track swelling and progression of local tissue effects.

Antivenom Adverse Reactions

Type I hypersensitivity reactions can be minor and local or severe and generalized. Clinical signs include facial swelling, hyperemia of the sclera or pinnae, agitation, bradycardia, tachycardia, vomiting, ptyalism, urticaria, facial pruritus, tachypnea, and/or fever. Most reactions can be treated by slowing the antivenom infusion rate. Additional treatments include diphenhydramine (2-4 mg/kg, IM) and +/- an anti-inflammatory dose (0.1 mg/kg/day), IV) of dexamethasone. Pretreatment with antihistamines or steroids is not recommended to influence development of Type I hypersensitivity.

Delayed Type III hypersensitivity reactions, or serum sickness, can manifest 3 to 21 days after antivenom administration and include fever, lethargy, diarrhea, painful joints, lymphadenomegaly, vasculitis, urticaria, and gastrointestinal signs. Treatment involves a tapering dose of glucocorticoids and antihistamines.12 For gastrointestinal signs, gastroprotection therapy can be initiated with a proton-pump-inhibitor (omeprazole PO 1 mg/kg q 12 hours or pantoprazole IV 1 mg/kg q 12 hours).

Anaphylaxis to antivenom is rare but can have an acute or a delayed onset. Reported anaphylactoid adverse reactions include Type I hypersensitivity clinical signs in addition to hypotension, dyspnea, shock, collapse, and death. Providers should be prepared to treat signs of anaphylaxis with an epinephrine CRI (0.1-1 mcg/kg/min IV) or bolus dosing (0.01 mg/kg, IV or IM), diphenhydramine (2-4 mg/kg IM), and +/- an anti-inflammatory dose (0.1 mg/kg/day, IV) of dexamethasone. Though an epinephrine CRI takes longer to set up, it has demonstrated superiority in the treatment and resolution of anaphylaxis over bolus dosing.7,8

Table 1. Snake Bite Severity Score