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This 25-year-old black woman presents to the emergency department (ED) 2 hours after the onset of lip swelling that has progressed to difficulty in breathing. With the exception of newly diagnosed hypertension, she is otherwise well. Last week, her primary care physician began a course of a new antihypertensive medication, lisinopril. She has had no history of swelling and there is no family history of disorders characterized by swelling. Her vital signs are temperature 37°C, heart rate (HR) 100 beats per minute (bpm), respiratory rate (RR) 22 breaths per minute, blood pressure (bp) 165/90 mm Hg, and SpO2 is 99% on 2 L·min−1 of O2 by nasal prongs.

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The patient is seated (Figure 24-1) with markedly edematous lips. She has a muffled voice (hot potato voice) and is unable to swallow her own secretions due to the swelling. There is no stridor. The remainder of the physical examination is unremarkable.

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24.2.1 What Is the Pathophysiology of Angioedema?

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Angioedema is defined as the abrupt onset of non-pitting swelling of the skin, mucous membranes, and deep subcutaneous tissues, including the linings of the upper respiratory and intestinal tracts.1 Angioedema develops because of a local increase in permeability of the submucosal or subcutaneous capillary vessels, causing local plasma extravasation. This is exacerbated by the release of vasoactive substances such as histamines, prostaglandins, bradykinins, and cytokines.2 Angioedema can be divided into hereditary angioedema (HAE) and acquired angioedema.

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Hereditary angioedema is extremely rare, affecting 1 in 50,000 people.2 It develops due to a C1 esterase inhibitor deficiency, which is inherited in an autosomal dominant pattern. This deficiency results in an abnormal increase in the activation of C1 and subsequently excessive formation of the enzyme kallikrein. The excess kallikrein transforms kininogen into kinins, including bradykinin. Bradykinin is highly vasoactive and produces the characteristic tissue swelling.2 HAE is commonly precipitated by trauma and stress, and can recur. If the patient has known HAE, then treatment with fresh frozen plasma (FFP) is beneficial, as it contains C1 esterase inhibitor. In some centers, vapor-heated C1 inhibitor concentrate is available and is proving beneficial in recurrent attacks of HAE.2

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Acquired angioedema is due to faulty activation of the complement and kallikrein–kinin systems. It comprises several types, including the traditional IgE-mediated allergic response, precipitated by exposure to an allergen (such as peanuts, antibiotics, and shellfish). Anaphylaxis is characterized by an acute onset and not only causes angioedema of the upper airways but also has a more systemic effect causing wheeze secondary to bronchoconstriction and hypotension secondary to vasodilation and third spacing.3 Anaphylaxis (or anaphylactoid) reactions can cause angioedema through other mechanisms such as direct mast cell degranulation (opiates, radio-contrast media) or by altering arachidonic acid metabolism (benzoates, angiotensin-converting enzyme inhibitors ...

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