hey, does anyone want me to share the abysmal paper i wrote in college on crotalid envenomation of canines?
THERE ARE FIVE NOTES ON THIS SO HERE WE GO.
The first thing is a link: https://docs.google.com/document/d/1YAcSazJu9F-WHLoggdDJYOXCg2uZuhTb_mQw6OBAFPo/edit?usp=sharing
If you want to see it in its original format with references and all. Underneath the cut is just The Words™
The emergency
Envenomation by a North American Crotalid is, simply put, a North American pit viper bite. Pit Vipers include: rattlesnakes, water moccasins, and copperheads (Najman DVM, DACVECC & Seshadri DVM, DACVECC, DAVBP, 2007). Dogs are more likely to be bitten on their faces, necessitating immediate treatment as Crotalid venom is neurotoxic and hemotoxic (Seibold DVM, DACVECC, 2007), i.e. it negatively affects the nervous system and the blood of the victim.
Presenting signs
The patient will usually be brought in by the owner after the owner has either witnessed the bite or heard the tell-tale rattle of a rattlesnake (Seibold DVM, DACVECC, 2007). When first examining the dog, you may see puncture wounds, but these may be closed due to edema around the site (Seibold DVM, DACVECC, 2007). Other signs may include: local tissue damage, tachycardia, ataxia, depressed mentation, dilated pupils, hyper-salivation, and pain at or around the site of the bite (Argo BS, 2011).
First Aid
It is important to explain basic first aid to the client if they call you before arriving. Tell them to apply a dry, room temperature compress to the site (Argo BS, 2011); such as a scarf, t-shirt, towel, or even a pair of clean socks. Make sure they keep the dog calm, as excitement will cause the venom to travel faster through the blood stream (Argo BS, 2011).
Remember to tell them that they must never apply a tourniquet tightly or for more than fifteen minutes if the injury is to a limb as this may cut off the blood supply and the dog may lose the limb (Argo BS, 2011). They must also never cut the wound open to suck the venom out as this is contraindicated in dogs because it can cause more tissue damage (Fogle DVM, DACVIM, 2004).
When they arrive at the clinic, be sure to remember your ABCs and make sure the animal has a patent airway, that they are breathing, and that they have a pulse and heartbeat (Najman DVM, DACVECC & Seshadri DVM, DACVECC, DAVBP, 2007). Administer CPCR or an endotracheal tube if necessary.
Emergency Treatment Drugs
Depending on the circumstances and the opinion of your Veterinarian, you may want to administer Diphenhydramine before the antivenin. Diphenhydramine blocks H1 receptors and will suppress the inflammatory response caused by the release of histamine into the bloodstream (Papich, 2011); this action may decrease an anaphylactic response to the antivenin. Diphenhydramine should be administered intramuscularly (IM) at a dose of 2-4mg/kg (Seibold DVM, DACVECC, 2007).
Antivenin is made of purified antibodies from a horse or sheep that work by attaching to the venom molecules and neutralizing them in addition to keeping them away from nervous and blood tissues, causing easier elimination from the dog’s body (Department of Surgical Education, Orlando Regional Medical Center, 2007). The first type of antivenin is the drug of choice for treating envenomation in dogs. Crotalid polyvalent antivenin is manufactured by Fort Dodge Animal Health and is made from horse antibodies (Najman DVM, DACVECC & Seshadri DVM, DACVECC, DAVBP, 2007). You administer this Antivenin intravenously (IV) in doses of one to five 10ml bottles at first (Fogle DVM, DACVIM, 2004). It may be necessary to administer more every two to four hours for effective treatment (Fogle DVM, DACVIM, 2004). Some dogs may be allergic to this antivenin and show signs of anaphylaxis or serum sickness (Fogle DVM, DACVIM, 2004). Serum sickness has not been well documented in dogs (Fogle DVM, DACVIM, 2004), but signs in humans can include: pyrexia, pruritus, arthralgia, swollen lymph nodes, urticaria, and dermatitis (Dugdale III, MD, 2012).
The second type of antivenin is called Crotalid polyvalent immune Fab, or CroFab, for short (Seibold DVM, DACVECC, 2007). It is manufactured by BTG International from sheep antibodies and is currently the antivenin of choice for use in humans. Not much is known about its efficacy in the canine patient (Seibold DVM, DACVECC, 2007).
Analgesia should be administered to the patient, as the bite of a viper is excruciatingly painful. Butorphanol is a good choice because it has limited effects on the respiratory and cardiovascular systems, though the patient should be monitored constantly for signs of respiratory depression (Papich, 2011). This opioid is a mixed agonist/antagonist, making it effective analgesia while still keeping side effects minimal (Papich, 2011). Butorphanol should be administered in doses of 0.1 – 0.2mg/kg every four hours, IV (Fogle DVM, DACVIM, 2004).
If the veterinarian chooses not to administer antivenin in cases where anaphylaxis is a concern, Dexamethasone sodium phosphate, a corticosteroid, can be given (Fogle DVM, DACVIM, 2004). It inhibits the action of the phospholipase component of the Crotalid venom and like all corticosteroids, inhibits the inflammatory response (Fogle DVM, DACVIM, 2004). Up to three doses of 0.5 – 1mg/kg may be given IV or IM, though IV is the preferred route of administration and because it is quicker and is absorbed more efficiently (Fogle DVM, DACVIM, 2004). Side effects to watch out for include: immune suppression, delayed healing, polyphagia, polydipsia, polyuria, diabetes, hyperlipidemia, hepatopathy, decreased thyroid hormone, GI ulceration, and decreased protein synthesis (Papich, 2011). The side effects of Dexamethasone however, are likely only to occur with long term use of the drug.
Broad spectrum antibiotics should be given to the patient IV until such time as the patient can take them orally (Seibold DVM, DACVECC, 2007). Ampicillin is one such antibiotic. Ampicillin acts by inhibiting bacterial cell wall synthesis (Papich, 2011) and should be administered IV at a dose of 22mg/kg three times a day (tid) (Seibold DVM, DACVECC, 2007). Be watchful for anaphylaxis associated with penicillin allergies (Papich, 2011).
Cefazolin is another option as an antibiotic. It should also be given IV at a dose of 22mg/kg tid (Seibold DVM, DACVECC, 2007). It too, inhibits cell wall synthesis and is more active against gram-negative bacteria than other cephalosporins (Papich, 2011). This drug can also cause anaphylaxis, this time associated with cephalosporin allergy (Papich, 2011).
Fluid therapy
IV fluid therapy should be started for the patient as soon as possible to correct the issue of shock. Crystalloid fluids such as Lactated Ringers Solution, which contains Sodium Chloride, Sodium lactate, potassium chloride, and calcium chloride, or 0.9% Normal saline, can be given to reduce hypotension, increase renal flow and diuresis, and maintain circulatory volume (Fogle DVM, DACVIM, 2004). The emergency rate for these fluids for the canine patient is 90mL/kg/hr or 10mL/lb/15 minutes. Constantly check vitals to assess the capillary refill time, mucous membrane color and character, pulse quality, blood pressure, and auscultate the lungs for crackling noises that mean the fluid rate is too high and is causing pulmonary edema. When the patient is stable, maintain them on maintenance fluids at a rate of ((30 x kg) + 70) mL/24hours to promote diuresis as snake venom can cause acute renal failure by the destruction of blood vessels (Fogle DVM, DACVIM, 2004).
Diagnostic procedures
A full CBC, or complete blood count, should be run as soon as the patient is stable and is out of immediate danger. 70%-90% of the time a blood smear from a dog bitten by a rattlesnake will show Echinocytes, red blood cells that have been crenated and look like burrs (Seibold DVM, DACVECC, 2007). The smear will also give some insight into whether the patient is having clotting problems, though a true platelet count on a hemocytometer is preferred. If thrombocytopenia, or low platelet count, is observed, this may indicate a decrease in the efficacy of primary hemostasis, where the platelets form a plug to prevent further blood loss while a more stable clot is being formed during secondary hemostasis. If thrombocytopenia is observed, then your veterinarian may order a buccal mucosal bleed time test to be performed to determine clotting times. Other parts of the CBC, such as the PCV, or packed cell volume, and TP, or total protein, may be elevated (Seibold DVM, DACVECC, 2007).
A buccal mucosal bleed time test is performed by tying the upper lip of the patient up with gauze and making two puncture wounds with a lancet, then taking a circular swatch of an absorbent material like a paper towel and blotting the blood from the wounds (Hendrix DVM PhD & Sirois EdD, MS, RVT, 2007). Make sure you do not disturb the clot forming at the wound site. The normal clotting time for dogs is one to five minutes (Hendrix DVM PhD & Sirois EdD, MS, RVT, 2007).
Prothrombin Time tests (PTT) and Activated Prothrombin Time tests (aPTT) should be taken every six to eight hours after envenomation because disseminated intravascular coagulopathy, or DIC, may develop even after administration of the antivenin. If either of these tests has a prolonged clotting time the patient may require plasma infusion therapy to replace the damaged proteins with functional ones.
The PTT tests for the efficacy of secondary hemostasis and for the clotting factors of the extrinsic pathways (Hendrix DVM PhD & Sirois EdD, MS, RVT, 2007), which are: I, II, V, VII, and X. If the time of the test is prolonged, it may indicate a decrease in the efficacy of secondary hemostasis as the normal time in canines is 7-10 seconds (Hendrix DVM PhD & Sirois EdD, MS, RVT, 2007). To perform this test you must take a sample in a blue top vacutainer tube, one that has the anticoagulant sodium citrate in it (Hendrix DVM PhD & Sirois EdD, MS, RVT, 2007). You then spin the vacutainer down and separate the plasma out by putting it in a red top tube. After that, you add a reagent to the plasma to recalcify the sample and start timing (Hendrix DVM PhD & Sirois EdD, MS, RVT, 2007).
The aPTT tests for the intrinsic pathway clotting factors (Hendrix DVM PhD & Sirois EdD, MS, RVT, 2007) e.g. XII, XI, IX, and VIII. , This sample is also taken in a blue top tube, spun down to collect the plasma and reagents are added to start the clotting process (Hendrix DVM PhD & Sirois EdD, MS, RVT, 2007). Both of these tests can be automated with the right kind machinery.
A chemistry panel may also be run, and this test may show elevated liver and renal enzymes (Seibold DVM, DACVECC, 2007). This may progress to a more serious condition of hypoalbuminemia if the edema is severe enough or if vasculitis is present (Seibold DVM, DACVECC, 2007).
Patient discharge information
The client will be given detailed information on the treatments, diagnostics, and long term home treatment of the patient. Instructions will include that the client needs to be aware that there may be massive skin sloughing, i.e. dead tissue will be separating from healthy, living tissue and coming off of the patient’s injury site(Fogle DVM, DACVIM, 2004). Explain that the bandages need to be kept clean and dry, while making sure that the bandage covers the whole wound site. Also tell the client to watch for any swelling and to wash the wound with sterile saline (Ward DVM), given to him or her by the clinic and a demonstration given by the technician, before applying a new bandage each day. The client will also need to receive an e-collar as the dog is likely to chew the bandage off and cause infection by licking at the wound (Ward DVM).
Broad spectrum antibiotics should be given to the client upon discharge as well. Ampicillin is a good choice at a dose of 20-40mg/kg and should be given every eight hours by mouth (Papich, 2011) for as long as the veterinarian prescribes it. The importance of finishing out the prescribed dose should be pressed upon the client.
Medicine for pain management should also be sent home with the client. Avoid NSAIDs (non-steroidal anti-inflammatory drugs) as they may cause coagulation abnormalities even after recovery (Fogle DVM, DACVIM, 2004). In a 10-20 kg dog, a Fentanyl patch at a dose of 50mcg/hr every three days may be appropriate (Papich, 2011). Side effects of this opioid analgesic are rare, but slight skin irritation may occur at the site of the patch (Papich, 2011). Clients should wear gloves when applying the patch to their dog’s skin so as to avoid an accidental dose (Papich, 2011).
Shock
Shock, simply put, is systemic hypoperfusion, a lack of blood flow to tissue. Early stages of shock are called hyperdynamic shock and have signs that are quite different from late stage or, hypodynamic shock (McCurnin DVM, MS, DACVS & Bassert VMD, 2010). Hyperdynamic shock is indicated by a bounding pulse, brick red mucous membranes, an increased heart rate and respiration rate as the animal’s body tries to compensate for the disease or injury that cause shock to occur(McCurnin DVM, MS, DACVS & Bassert VMD, 2010). Hypodynamic shock is indicated with pale mucous membranes, a weak and thready pulse, and weakness (McCurnin DVM, MS, DACVS & Bassert VMD, 2010). This type of shock will occur if the hyperdynamic mechanisms fail (McCurnin DVM, MS, DACVS & Bassert VMD, 2010).
There are four types of shock that merely differ in their mechanism of action (McCurnin DVM, MS, DACVS & Bassert VMD, 2010). Hypovolemic shock is the most common in small animals and is caused by a lack of intravascular volume caused by blood loss or severe dehydration (McCurnin DVM, MS, DACVS & Bassert VMD, 2010). Obstructive shock is caused by a physical obstruction of the blood flow in the patient’s body (McCurnin DVM, MS, DACVS & Bassert VMD, 2010). This can occur due to a thromboembolism, or even a dislodged Dirofilaria immitis, or heartworm. Cardiogenic shock is cause by heart failure (McCurnin DVM, MS, DACVS & Bassert VMD, 2010). The heart’s preload and afterload increase, but the contractility decreases (McCurnin DVM, MS, DACVS & Bassert VMD, 2010). Last is Distributive shock, this can be caused by sepsis, anaphylaxis, heatstroke, trauma, or envenomation (McCurnin DVM, MS, DACVS & Bassert VMD, 2010). The blood is still in the patient’ body, but it is not where it is supposed to be and is pooling in the capillaries (McCurnin DVM, MS, DACVS & Bassert VMD, 2010).
Distributive shock is the type of shock that would be dealt with in the case of a rattlesnake envenomation, but all shock is dealt with the same way. Fluids should be administered at emergency rates, as mentioned previously. The patient should be started on pure oxygen either by mask, intubation, or flow by (McCurnin DVM, MS, DACVS & Bassert VMD, 2010).
Shock is a secondary condition that is best resolved by taking care of the underlying cause (McCurnin DVM, MS, DACVS & Bassert VMD, 2010). In the case of envenomation, treatment is the antivenin. The patient is stable when the heart rate has normalized, the systolic blood pressure has stabilized at 90mmHg or has gone higher, and the mucous membranes are no longer white with a prolonged CRT (McCurnin DVM, MS, DACVS & Bassert VMD, 2010).
Conclusion
Crotalid envenomation, while being a life threatening issue, does not have high mortality rates if proper treatment is given. The presenting signs and history give clear insight into the cause of the emergency and treatment can be quick and decisive. Once the patient is stable and the antivenin is given success rates are high and death is often avoided. The diagnostic tests that are done give more insight into the continued good prognosis of the patient.
thisacelovesheadcanons 