Today's Veterinary Practice

JUL-AUG 2017

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

Issue link: http://todaysveterinarypractice.epubxp.com/i/840151

Contents of this Issue

Navigation

Page 55 of 79

54 ANAPHYLACTIC SHOCK PEER REVIEWED antibodies cause mast cell and basophil activation and start the immediate hypersensitivity reaction. Cross-linking induces a membrane change, causing an influx of calcium ions into the cell that initiates degranulation and, thus, a release of mediators (eg, histamine). Interactions between mediators and host organs cause clinical signs to appear. 2 Anaphylactoid Reaction: Immunologic IgE Independent In contrast, immunologic IgE-independent reactions occur through IgG antibody production. Allergen exposure activates IgG antigen binding to low-affinity receptors on macrophages. IgE-independent reactions require Specific Causes of Anaphylaxis Hymenoptera Hymenoptera is an order of insects that includes bees, wasps, and ants. The venom of each species has different effects in patients. Bees Bees pose an anaphylactic threat because the venom in their stings contains peptide 401, phospholipase A2, melittin, and hyaluronidase. Peptide 401 is also known as mast cell–degranulating peptide and causes histamine release. Phospholipase A2 works with melittin to cause intravascular hemolysis. Hyaluronidase changes vascular permeability by disrupting collagen and allowing other venom components to penetrate cells. Melittin hydrolyzes cell membranes, thus altering permeability. It also causes biogenic amines and potassium to leak from cells and induces catecholamine release. Melittin is the primary cause for localized pain. 4,5 A bee can only sting once because of the barbs on its stinger. Wasps and Hornets Wasps, unlike bees, have smooth stingers and may sting multiple times. They are much more aggressive than bees. Hornets defend their nests aggressively and have much more painful stings than either wasps or bees due to the amount of acetylcholine in their venom. Wasp and hornet stings contain the same proteins associated with bee venom with the exception of melittin. Bites and stings may produce a toxic envenomation response. The estimated lethal dose is 20 stings/kg. 5 Fire Ants Fire ants can be very aggressive. They attach to their prey with their mandibles and may sting with a nonbarbed stinger multiple times. Their venom contains hyaluronidase, phospholipase, and water-insoluble alkaloid compounds. Alkaloid venom causes cytotoxic, hemolytic pustules. Fire ants do not elicit an IgE- mediated anaphylactic response but an anaphylactoid one. 6 Other Causes Other common causes of anaphylactic reactions include ophthalmic antibiotic ointment (in cats), drugs (some chemotherapy agents, contrast material, and antibiotics), and blood transfusions. Ophthalmic Antibiotic Ointment in Cats In a retrospective evaluation of observed cases of anaphylaxis in cats that were administered a topical ophthalmic antibiotic, 56% of evaluated cats had anaphylactic reactions within 10 minutes. All ointments used contained polymyxin B. Clinical signs manifested in at least 2 body systems. Most commonly reported signs included respiratory and gastrointestinal compromise. Other organ systems involved were cardiovascular and cutaneous. Standard, symptomatic treatment aided in recovery; however, 13% of patients in this study died. 7 Contrast Agents A case study of 3 canine patients recorded severity of anaphylactoid reactions to magnetic resonance imaging contrast media in anesthetized patients. Clinical signs ranged from very mild (cutaneous edema, which resolved during recovery) to severe (cardiovascular collapse, which necessitated swift emergency care). 8 Blood Transfusions IgE-mediated anaphylactic reactions may occur in patients receiving blood transfusions because of the presence of IgE and mast cells. Reported mild clinical signs include edema, urticaria, vomiting, and dyspnea. At onset of mild signs, the transfusion should be stopped. If the signs resolve in a timely fashion, the transfusion may continue at a slower rate (25%–50%). If there is evidence of more severe clinical signs, the transfusion should be discontinued and emergency action taken. 9 shutterstock.com/nutsiam

Articles in this issue

Links on this page

Archives of this issue

view archives of Today's Veterinary Practice - JUL-AUG 2017