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Treatment of anaphylaxis in a dog | VETgirl Veterinary Continuing Education Videos

In this VETgirl online veterinary continuing education video, we discuss how to recognize and treat anaphylaxis in dogs. In this video, an 8-month-old, male neutered, Black Labrador presented for acute collapse. He was carried in by the pet owners and presented to the emergency room with pale gums and a CRT of > 3 seconds. The dog was actively vomiting and was extremely hypotensive, despite having a normal heart rate (making us highly suspicious of uncompensated shock). Based on the clinical presentation, our primary differential was severe anaphylaxis.

Anaphylaxis can present in different ways, depending on what “type” of allergic reaction it is. Type 1 hypersensitivity is immediate and is an immune response to antigen-specific antibody reactions, resulting in the release of histamine, leukotrienes, and bradykinins. Examples of this type are seen due to drug or food reactions (e.g., such as what is seen in people with peanuts, seafood, penicillin, etc.). This is considered “true” anaphylaxis, and is life-threatening, but rarely seen in veterinary medicine. Type II hypersensitivity reactions are considered cytotoxic and IgG and IgM dependent. Examples of this type include blood transfusion reactions. Type III hypersensitivity is due to immune complexes and is IgG and IgM complex dependent; examples include glomerulonephritis, immune-mediated joint disease, and vasculitis. Finally, Type IV is a delayed, T lymphocyte dependent reaction; examples include allergic contact dermatitis and rheumatoid arthritis.

In this video, anaphylaxis was most commonly due to an immunologic mechanism, in which IgE binds to the Ag, activating mast cells and causing a massive release of histamine. Again, anaphylaxis can be a rapid life threatening reaction, which can occur within minutes of exposure from an insect bite or sting, medications (e.g., vaccines), or no identified cause. Pets with a history of allergies tend to be more likely to develop anaphylaxis. This dog had a history of allergies, and was also being treated for heartworm disease.

Signs can present in any of the following manners:
1) Skin: generalized hives, angioedema, facial swelling or conjunctival swelling
2) Respiratory: bronchospasm, causing difficulty breathing and wheezing
3) Cardiovascular: Arrhythmias, tachycardia, bradycardia, hypotension
4) Gastrointestinal: Severe vomiting and diarrhea, commonly hemorrhagic

This dog was stabilized with 2 aliquots of fluid boluses (e.g., 20 mL/kg), a 10 mL/kg bolus of a colloid (e.g., Vetstarch), epinephrine and diphenhydramine. GI medications, such as maropitant, pantoprazole, or famotidine, are also commonly used, as histamine can stimulate increased acid production in the stomach. Steroids are commonly used to help reduce the risk of secondary allergic reactions, which usually will occur within 6 hours of the anaphylactic episode.

In 2009, Quantz et al correlated a thickened gallbladder wall, called the halo sign, with anaphylaxis in dogs. This is due to the liver and GI tract being the shock organ in the dog. As the shock organ of the cat is the lungs, cats do not get the halo sign. Using the diaphragmatic-hepatic (or DH) view of the AFAST3 ultrasound, a distinct halo sign was noted in this dog, further reinforcing the diagnosis of anaphylaxis. This gallbladder wall edema can occur within minutes of an anaphylactic reaction and is characterized by a hyperechoic inner and outer wall, with a sonolucent line between. This is a useful tool to immediately diagnose anaphylaxis, as the dramatic rise in ALT may take several hours. It is important to remember, however, that the gallbladder halo sign can be caused by other conditions, such as right-sided heart failure, pericardial effusion and tamponade, volume overload, vasculitis, gallbladder disease, and pancreatitis. Be careful and use the entire constellation of symptoms when diagnosing anaphylaxis.

Luckily, with a quick diagnosis and rapid treatment, this dog showed a dramatic recovery. To the owner’s disbelief, he was up and walking, with normal vitals, within 30 minutes of presentation.

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