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57 JULY/AUGUST 2017 ■ TVPJOURNAL.COM CONTINUING EDUCATION Respiratory Respiratory signs often result from laryngeal and pharyngeal edema, bronchoconstriction, and increased mucus secretion. They include dyspnea, bronchospasm, stridor, tachypnea, and coughing. Cardiovascular Because of the intensity of vasodilation during anaphylaxis, hypotension is the primary cardiovascular sign. Hypotension is further exacerbated by fluid extravasation as vascular permeability increases; intravascular blood volume can decrease up to 35%, leading to both a hypovolemic and a distributive shock state. 15 Tachycardia due to hypovolemia may also be present in anaphylaxis patients. Conversely, bradycardia may be caused by increased vagal reactivity. Careful auscultation may reveal cardiac arrhythmias. Signs of decreased perfusion may exist, including pale mucous membranes, increased capillary refill time, decreased pulses, hypothermia, and depressed mentation. Because of vasodilation, injected or "brick red" mucous membranes may be noted on physical examination. Gastrointestinal Gastrointestinal signs may include nausea, vomiting, and diarrhea. A recent study of 96 dogs revealed that during anaphylaxis, blood flow is altered throughout the liver (portal circulation) and gastrointestinal tract, and hepatocytes are directly affected, 17 resulting in excessive leakage of alanine aminotransferase (ALT). The ALT levels in this study increased in the first 12 hours and peaked 24 to 48 hours later. This study also revealed that changes in the gallbladder wall may be detectable on ultrasound evaluation almost immediately following an episode of anaphylaxis. Striations in the gallbladder wall ("halo effect") may be seen because of inflammation as well as impaired venous drainage. 17 Primary Clinical Signs in Dogs Cutaneous signs, such as urticaria, erythema, angioedema of the face and muzzle, hypersalivation, and pruritus, can be seen but may be subtle and short lived. 2 Hemorrhagic enteritis caused by portal hypertension is one of the most commonly noted clinical antemortem signs as visceral pooling of blood in the intestines increases, leading to vomiting and diarrhea. 12,16 As a result of the degree of liver involvement, dogs typically exhibit signs of cardiovascular impairment due to hepatic venous congestion. Other common clinical signs include hypotension and cardiovascular collapse; dyspnea, bronchospasm, and stridor may be noted as well. Primary Clinical Signs in Cats Cats typically exhibit respiratory and gastrointestinal signs. Respiratory distress is often the first sign exhibited. Cats' clinical signs may also include hypersalivation, laryngeal swelling, edema, pruritus, and signs of hypovolemic shock. 12,16 Cats are less likely than dogs to experience cutaneous effects. DIAGNOSTIC CRITERIA Anaphylaxis may be difficult to diagnose and is often overlooked. Diagnostic differentials include severe asthma, a vasovagal event, and neoplasia, such as a pheochromocytoma or mast cell tumor degranulation. 10 Rate of onset of clinical signs is an important diagnostic criterion. Anaphylaxis usually occurs within the first 30 minutes after allergen exposure and progressively worsens. However, a general rule of thumb is that the more quickly the signs manifest, the more severe the anaphylaxis will be. Box 1 presents criteria that can be used to assess the likelihood of anaphylaxis in a presenting patient. BOX 1. Likelihood of Anaphylaxis 12 Anaphylaxis is highly likely when any 1 of the following 3 criteria are fulfilled. 1. Acute onset of an illness with involvement of the skin, mucosal tissue, or both (ie, pruritus, edema, facial swelling), plus at least 1 of the following: a. Respiratory compromise (ie, dyspnea, bronchospasm, stridor, hypoxemia) b. Symptoms of end-organ dysfunction (ie, hypotension, syncope, incontinence) 2. Two or more of the following that occur rapidly after exposure to a likely allergen: a. Involvement of the skin-mucosal tissue b. Respiratory compromise c. Reduced blood pressure or associated symptoms d. Persistent gastrointestinal symptoms (ie, vomiting, diarrhea) 3. Reduced blood pressure after exposure to known allergen for that patient