Anaphylaxis

Key Features

Essentials of Diagnosis

• Anaphylaxis is an acute life-threatening clinical syndrome that occurs when large quantities of inflammatory mediators are rapidly released from mast cells and basophils after exposure to an allergen in a previously sensitized patient

• Anaphylactoid reactions

  • Mimic anaphylaxis but are not mediated by IgE antibodies

  • May be mediated by anaphylatoxins such as C3a or C5a or through nonimmune mast cell degranulating agents

• Idiopathic anaphylaxis by definition has no recognized external cause

General Considerations

• Common causes of anaphylaxis or anaphylactoid reactions

  • Drugs

    • Antibiotics

    • Anesthetic agents

  • Foods

    • Peanuts, tree nuts, shellfish, and others

  • Biologicals

    • Latex

    • Insulin

    • Allergen extracts

    • Antisera

    • Blood products

    • Enzymes

  • Monoclonal antibodies (eg, omalizumab)

  • Insect venoms

  • Radiocontrast media

  • Aspirin and other nonsteroidal anti-inflammatory drugs

  • Anesthetic agents

  • Idiopathic

Clinical Findings

Symptoms and Signs

• Onset typically occurs within minutes after exposure to the offending agent and can be short-lived, protracted, or biphasic, with recurrence after several hours despite treatment

• Anaphylaxis is highly likely when any one of the following three criteria is fulfilled:

  • Acute onset of an illness (minutes to several hours) with involvement of the skin, mucosal tissue, or both (eg, generalized hives, pruritus or flushing, swollen lips-tongue-uvula) and at least one of the following:

    • Respiratory compromise (eg, dyspnea, wheeze, bronchospasm, stridor, reduced peak expiratory flow, hypoxemia)

    • Reduced blood pressure or associated symptoms of end-organ dysfunction (eg, hypotonia [collapse], syncope, incontinence)

  • Two or more of the following that occur rapidly after exposure to a likely allergen for that patient (minutes to several hours):

    • Involvement of the skin-mucosal tissue (eg, generalized urticaria, itch-flush, swollen lips-tongue-uvula)

    • Respiratory compromise (eg, dyspnea, wheeze, bronchospasm, stridor, reduced PEFR, hypoxemia)

    • Reduced blood pressure or associated symptoms (eg, hypotonia [collapse], syncope, incontinence)

    • Persistent gastrointestinal symptoms (eg, crampy abdominal pain, vomiting)

  • Reduced blood pressure after exposure to a known allergen for that patient (minutes to several hours):

    • Infants and children: low systolic blood pressure (age specific) or greater than 30% decrease in systolic pressure

    • Low systolic blood pressure in children, defined as less than 70 mm Hg in those aged from 1 month to 1 year, less than (70 mm Hg + [2 × age]) in those 1–10 years of age, and less than 90 mm Hg in those 11–17 years

Differential Diagnosis

• Other causes of shock along with cardiac arrhythmias

• Respiratory failure associated with asthma

• Mastocytosis

• Hereditary angioedema

• Scombroid poisoning

• Vasovagal reactions

• Vocal cord dysfunction

• Anxiety attacks

Diagnosis

• Clinical history

Laboratory Findings

• An absence of laboratory findings does not rule out anaphylaxis

• Tryptase released by mast cells can be measured in the serum within 3 hours of onset of the reaction and may be helpful when the diagnosis of anaphylaxis is in question

• However, tryptase ...