Page 1842 - Cote clinical veterinary advisor dogs and cats 4th

924 Snake Envenomation (Pit Viper)

in severe cases, azotemia and hepatic enzyme treatment. For moderate cases (more severe for venom-induced coagulopathy is adequate
elevations can occur as injury progresses. swelling, mild systemic signs), typically 1-2 treatment with antivenom.
Creatine kinase level may be increased
VetBooks.ir • Urinalysis: hematuria, hemoglobinuria, minutes, and the patient is reassessed. Chronic Treatment
vials of antivenom are given over 30-60
secondary to tissue damage.
For severe cases (very severe swelling or
Surgical debridement of necrotic tissue is
or myoglobinuria is possible (avoid
be administered at initiation of treatment.
cystocentesis). severe cardiovascular signs), 2-4 vials can sometimes necessary; most cases of necrosis
become apparent by day 3-5. Occasionally,
• Baseline arterial blood pressure measurement These severely affected patients may wounds with severe necrosis become infected;
(p. 1065): normal or low require further treatment with antivenom antibiotic therapy is indicated in these cases.
• Coagulation profile (p. 1325): prolonged even if their signs initially stabilize; watch Rarely, a recurrence of envenomation occurs
activated clotting time (ACT), prothrom- for recurrence of clinical signs. Dosing of after improvement with antivenom administra-
bin time (PT), partial thromboplastin antivenom is controversial because venom tion; it is thought that this is due to a depot
time (aPTT); thromboelastography (TEG) concentration assays are not rapidly avail- of venom that was mobilized anew. This is
evidence of hypocoagulability and/or able; the key is to use enough antivenom associated with a worsening of clinical signs and
hyperfibrinolysis to control and reverse the clinical signs. may merit another treatment with antivenom.
In general, the more severely affected the
Advanced or Confirmatory patient, the more antivenom is required. Nutrition/Diet
Testing Provide adequate antivenom promptly and Almost all snake bite victims surviving the
Echinocytes on a blood smear are a common continually reassess the patient’s need for initial intoxication begin to eat in 1-3 days. In
finding in envenomated animals. Echinocytes ongoing treatment. patients with severe wounds around the mouth,
are burred red blood cells that appear soon ○ Several antivenoms are now available in nasoesophageal or esophagostomy feeding tubes
after envenomation and last in circulation the United States. may be indicated until they can comfortably
24-48 hours. ■ Lyophilized products requiring reconsti- eat (pp. 1106-1107).
tution: Antivenin Crotalidae Polyvalent
TREATMENT (ACP; Boehringer Ingelheim, St Joseph, Behavior/Exercise
MO); CroFab (polyvalent immune Rest until recovered
Treatment Overview Fab-ovine; BTG International, West
Goals are management/prevention of hypoten- Conshohocken, PA); the Fab1 product Possible Complications
sion, neutralization of venom (minimizing local is less antigenic, dissolves more rapidly Monitor during infusion because antivenom
and systemic effects), pain management, and and is more potent but is extremely may cause an anaphylactic reaction (p. 54).
avoidance of iatrogenic complications (par- expensive. • Signs of mild to moderate anaphylaxis
ticularly during administration of antivenom). ■ New equine-origin products that do include salivation, vomiting, abdominal
not require reconstitution: VenomVet pain, hives, and fever.
Acute General Treatment (Instituto Biologica Argentino, Buenos • Signs of severe anaphylaxis also include
• All animals that are bitten by a snake, regard- Aires, Argentina) and Rattler Antivenin collapse, pale or white mucous membranes,
less of their apparent hemodynamic stability, (Mg Biologics, Ames, IA) severe hypotension, cardiac arrhythmias, or
should be hospitalized for a minimum of 8 • Antibiotics (controversial): not usually sudden death.
hours to assess for delayed clinical signs that required. If wound infection occurs (usually • Anaphylaxis can usually be treated if rec-
manifest during this period. after day 3), choose a broad-spectrum ognized at an early stage. Life-threatening
• IV fluid therapy antibiotic with adequate gram-negative reactions can occur with infusion of even
○ First line of therapy is to treat hypotension coverage while cultures are pending. Routine tiny amounts of antivenom.
or hypovolemic shock (p. 911). culture of bite wounds is probably not • Treatment includes
○ Crystalloids (e.g., lactated Ringer’s helpful. ○ Epinephrine 0.01 mg/kg IV in severe cases
solution) to replace deficit and provide • Analgesics: opioids should be used judi- or IM in milder cases; in very severe cases,
replacement of ongoing losses and normal ciously. Avoid sedation initially because repeated doses q 3-5 minutes or CRI may
maintenance. For hypovolemic patients, mental status is an excellent clinical indicator be necessary.
initial bolus doses of 20-30 mL/kg over of response to treatment. Options include ○ Glucocorticoids (e.g., dexamethasone
10-15 minutes followed by reassessment buprenorphine 0.01-0.02 mg/kg IV q 0.25 mg/kg IV or IM)
and repeat as required. 6-8h, hydromorphone 0.05-0.1 mg/kg IV ○ H1-blockers (e.g., diphenhydramine 2 mg/
• Antivenin (Crotalidae) polyvalent q 4-6h, fentanyl continuous-rate infusion kg IM)
○ Administered immediately for viper bites (CRI) 2-5 mcg/kg/h after loading dose of ○ H2-blockers (e.g., famotidine 1 mg/kg IV
that cause moderate to severe systemic 1-3 mcg/kg IV. or IM)
signs (e.g., hypotension, hemorrhage, • Nonsteroidal antiinflammatory drugs should • Acute kidney injury can occur due to
neurologic abnormalities). It increases be avoided due to potential for nephrotoxico- pigmenturia from hemolysis and/or rhabdo-
survival when given closer to time of bite, sis in hypovolemic patients and their effects myolysis. Risk is reduced by use of antivenom
but beneficial effects noted for at least 60 on platelet function. to prevent further hemolysis, adequate
hours after envenomation. Most victims of • Glucocorticoids and antihistamines: not crystalloid fluid therapy, and avoidance of
pygmy rattlesnake and copperhead bites recommended (unless anaphylaxis) artificial colloids.
do not require antivenom. • Urgent airway management: rarely needed
○ A dosage of up to 6-25 vials of polyvalent in dogs; dogs with bites inside the mouth Recommended Monitoring
immune Fab-ovine is recommended in (e.g., on the tongue) are the exception (p. • Respiratory rate and effort, blood pressure,
humans after crotalid envenomation; 1166). electrocardiogram, urine color/output, and
however, patients with less severe clini- • Transfusion (p. 1169) is indicated in patients mentation
cal signs may not require this amount of with clinically significant anemia secondary • Reassess fully if deteriorating mentation is
antivenom. For dogs, a mild case (mild to hemorrhage or hemolysis. Fresh-frozen recognized. Recheck packed cell volume
localized swelling only, no other clinical plasma is sometimes used when a coagulopa- (PCV), total protein, blood lactate concentra-
signs) usually does not require antivenom thy is not improving, but the best treatment tion, ± coagulation status q 6-12 hours for

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