Anaphylaxis
Anaphylaxis is a potentially life-threatening multisystem allergic reaction that can be triggered by a variety of agents (Table 2.1). The mechanism may be either IgE-mediated (anaphylactic reaction) or non-IgE-mediated (anaphylactoid reaction). Each process, however, leads to the release of immune mediators from mast cells and basophils, so the clinical presentation and treatment is similar and the term “anaphylaxis” is often applied to both.
| Anaphylactic (IgE dependent) |
| Animal dander |
| Antibiotics: beta-lactams, sulfonamides |
| Colorants (carmine dye) |
| Foods: shellfish (crustaceans, mollusks), peanuts, tree nuts (pecans, pistachios, walnuts), egg whites, fish, wheat, milk, soy, sesame |
| Hormones (estrogen, progesterone) |
| Hymenoptera sting (yellow jacket, hornet, wasp, honeybee, fire ant) |
| Latex |
| Anaphylactoid (IgE-independent) |
| Immune aggregates |
| IV Immunoglobulin |
| Medications: opioids, muscle relaxants, nonsteroidal anti-inflammatories, aspirin |
| Physiologic factors: exercise, cold temperature, heat, pressure, sunlight |
| Radiocontrast material (any) |
| Transfusion reaction |
| Idiopathic |
Clinical Presentation
Anaphylaxis can present with a variety of signs and symptoms (Table 2.2). It involves at least two organ systems, most commonly cutaneous, respiratory, gastrointestinal, and/or cardiovascular. A reaction can occur as rapidly as seconds after exposure or it may be delayed for hours. Up to 20% of patients with a severe allergic reaction will have a biphasic response, with symptoms recurring 1–72 hours (average eight hours) after the initial reaction has remitted. In protracted anaphylaxis, symptoms may persist for up to 32 hours.
| Organ system | Signs and symptoms | Frequency (%) |
|---|---|---|
| Cutaneous | Urticaria, angioedema | 88 |
| Cutaneous | Flushing | 46 |
| Cutaneous | Pruritus (no rash) | 5 |
| Respiratory | Wheezing, dyspnea, stridor | 50 |
| Gastrointestinal | Nausea, vomiting, diarrhea, abdominal pain | 30 |
| Cardiovascular | Syncope, hypotension, arrhythmias | 30 |
| Miscellaneous | Sense of impending doom, seizure, diaphoresis, rhinitis, headache, metallic taste | 1–20 |
Diagnosis
The diagnosis of anaphylaxis is based on clinical manifestations fulfilling one of the following three criteria:
1. Acute onset with involvement of skin and/or mucosal tissues and at least one of the following:
a. respiratory compromise
b. hypotension
c. evidence of end-organ dysfunction.
2. Rapid onset of involvement in two or more organ systems after exposure to a known allergen.
3. Hypotension after exposure to a known allergen.
The differential diagnosis of anaphylaxis is summarized in Table 2.3.
| Diagnosis | Differentiating features |
|---|---|
| Airway foreign body | Aspiration history |
| Auscultatory findings may be localized | |
| Angioedema | No respiratory symptoms |
| Asthma | Involves only the respiratory system |
| Cardiac tamponade | Muffled heart sounds, pericardial rub, pulsus paradoxus |
| Croup | Barking cough |
| Food poisoning | Scombroid |
| Flushing syndromes | Catecholamine excreting tumors; carcinoid |
| Globus hystericus | Sensation of a lump in the throat |
| Hereditary angioedema | May have a history of previous similar episodes |
| Panic attack | Precipitating event |
| No cutaneous findings | |
| Pulmonary embolism | Pleuritic pain, fourth heart sound |
| Jugular venous distension | |
| Red man syndrome | History of vancomycin exposure |
| Serum sickness | Fever, lymphadenopathy, arthralgias/arthritis |
| Urticaria | Skin is sole organ system involved |
| Vasovagal episode | Gradual onset after precipitating event |
| Vocal cord dysfunction | Onset is not acute |
ED Management
Anaphylaxis is a medical emergency requiring immediate attention. Institute the ABCs of emergency care. Limit any continued exposure and discontinue any intravenous agents immediately. Avoid using latex products when caring for a latex-allergic patient. If the affected patient is taking beta-blocking medication, be prepared for a difficult recovery; sometimes extraordinary efforts are required to overcome beta-blockade associated with anaphylaxis.
The first priority is to maintain airway patency. If adequate ventilation and oxygenation are documented by pulse oximetry, do not change the patient’s position, but administer 100% oxygen as tolerated. Place a hypotensive patient in the recumbent position and elevate the lower extremities. If stridor is present, prepare to intubate the patient if initial therapy with epinephrine (see below) is not effective. Monitor the ECG and oxygen saturation continuously, and if the patient is tachycardic or hypotensive, establish IV access and give a 20 mL/kg normal saline bolus. Make a rapid assessment of the rate of progression and the extent of the reaction.
Epinephrine
Epinephrine is the mainstay of treatment of anaphylaxis. The alpha-adrenergic effects reverse peripheral vasodilation, decreasing hypotension and reducing angioedema and urticaria; the beta-adrenergic effects cause bronchodilation, increase myocardial contractility, and suppress further release of mast cells and basophils.
For a normotensive patient, give 0.01 mL/kg (0.5 mL maximum) of 1:1000 epinephrine intramuscularly. Repeat the dose every 5–15 minutes, as needed.
Give a hypotensive patient 0.01 mg/kg (0.1 mL/kg, 10 mL maximum) of 1:10,000 epinephrine intravenously. Repeat every 3–5 minutes. If venous access is not available, administer epinephrine (0.1 mL/kg of 1:1000) via the endotracheal tube. If the initial response to epinephrine is inadequate, use an intravenous drip, starting with 0.1 mcg/kg/min (1.5 mcg/kg/min maximum).
Vasopressor Infusion
A vasopressor infusion is indicated for hypotension refractory to epinephrine and volume repletion. Give dopamine at 2–20 mcg/kg/min.
Antihistamines
H1 and H2 antihistamines block the effect of circulating histamines but do not decrease mediator release. H2 blockers may also inhibit the histamine effects on peripheral vasculature and myocardial tissues. The onset of action of antihistamines is delayed, so epinephrine is still necessary. Give diphenhydramine (H1), 1–2 mg/kg IV or PO q 6 h (50 mg/dose maximum, 200 mg/day maximum) and ranitidine (H2), 2 mg/kg q 6–8h IV or PO (50 mg/dose maximum).
Albuterol
Treat bronchospasm resistant to epinephrine with nebulized albuterol 0.15 mg/kg/dose, either hourly or continuously (2.5 mg minimum, 10 mg maximum). See Asthma (p. 625) for the treatment of bronchospasm not responsive to albuterol.
Corticosteroids
Give systemic corticosteroids to a patient with a history of asthma, idiopathic anaphylaxis, or severe or prolonged symptoms. Steroids may also reduce the risk of recurrent or protracted anaphylaxis. Use methylprednisolone 1–2 mg/kg/day divided q 6 h IV (60 mg/day maximum) or prednisone 1–2 mg/kg/day PO (60 mg/day maximum), for three days.
Glucagon
Anaphylaxis may be very difficult to treat in a patient taking beta-adrenergic blockers, which blunt the response to epinephrine. The patient is at increased risk for bronchospasm, hypotension, and paradoxical bradycardia. Glucagon has both inotropic and chronotropic effects that are mediated independently of alpha- and beta-receptors and therefore can reverse refractory hypotension and bradycardia. Give a loading dose of 20–30 mcg/kg IV (1 mg maximum) over five minutes, followed by a continuous infusion of 5–15 mcg/min, titrating the dose to the desired blood pressure. Glucagon may cause emesis; therefore, protect the airway if the patient is drowsy or obtunded.
Discharge Considerations
1. Observe for 6–8 hours. Most late-phase reactions occur within this time period.
2. Give prednisone 1–2 mg/kg/day (60 mg/day maximum) for three days.
3. Give diphenhydramine (5 mg/kg/day div q 6h, 50 mg/dose maximum) for 2–3 days to treat urticaria.
4. Give an H2 antihistamine, ranitidine (2 mg/kg q 6–8h, 50 mg/dose maximum) for 2–3 days.
5. Prescribe injectable epinephrine (EpiPen Jr. <30 kg, EpiPen >30 kg) and instruct the parent and/or child when and how to administer it in the anterolateral aspect of the thigh, through the clothing, while avoiding placing the thumb over the tip.
6. Educate the family regarding avoidance of the trigger(s).
7. Inform the family about MedicAlert bracelets (1-888-633-4298 or www.medicalert.org).
8. Refer all patients with an episode of anaphylaxis to an allergist.
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