Anaphylaxis

Anaphylaxis (Table 10) is a Type I hypersensitivity reaction. Initial exposure to an allergen results in antigen-specific antibody production dominated by the immunoglobulin E (IgE) isotype. Following re-exposure, IgE antibodies bind to mast cells and basophils associated with mucosal and epithelial tissues. The simultaneous binding of an antigen to adjacent IgE molecules fixed to Fc receptors triggers degranulation of mast cells and basophils resulting in the release of histamine, leukotrienes, prostaglandins, chemokines, enzymes and cytokines in target tissues.

Table 10. Anaphylaxis.

Prevention:

Identify at-risk patient
- A negative history of prior anaphylactic reaction does not rule out the possibility of a type I allergic reaction

Signs and symptoms:

1 to 15 minutes following exposure to a specific allergen
- Pruritus, urticaria, angioedema
- Coughing, stridor, dyspnea, wheezing,
- Agitation, flushing, palpitation
- Unresponsiveness, convulsion,
- Hypotension, cardiogenic shock

Emergency response:

Place patient in a supine position
- Select an auto-injector with the appropriate dosage strength predicated on the patient’s body weight: patients ≥30 kg (≥66 pounds): 0.3 mg
  - Remove the auto-injector from its protective case
  - Check to make sure the expiration date has not passed.
  - Confirm that the liquid inside the auto-injector is not discolored (i.e., not pinkish or brownish), cloudy, and is free of particles.
- Grasp the auto-injector in the dominant hand, with thumb closest to the safety cap; and, with the other hand, remove the cap.
  - Hold the patient’s leg to keep it steady while injecting.
    - Place (jab) the needle end of the auto-injector at right angle against the anterolateral aspect of the thigh.
    - The needle is designed to go through clothing.
  - Press on the auto-injector firmly to release the needle and inject the epinephrine.
  - Remove the auto-injector and massage the injection site for 10 seconds.
    - Some auto-injectors have a needle that retracts back into the case after use.
    - If the needle remains exposed, insert the injector (needle first) back into its case.
  - Immediately following the administration of epinephrine, the patient must be referred for additional medical care – Call 911.
    - Tell the dispatcher you just administered epinephrine to a patient to treat a suspected anaphylactic reaction.
  - With severe persistent anaphylaxis a repeat injection of epinephrine, with an additional auto-injector, may be necessary in 15-20 minutes.
    - More than two sequential doses of epinephrine should not be administered without direct medical supervision of the patient.
  - Do not discard the auto-injector
- Patients with stridor and wheezing unresponsive to epinephrine should be given O₂
  - 4 to 6 L/minute by nasal cannula
- Monitor vital signs
  - If at any time the patient becomes unresponsive, no normal breathing, and no palpable pulse consider the diagnosis of cardiac arrest
    - Immediate CPR and defibrillation congruent with current recommendations.

Nota bene:

Signs of recovering: character of respiration returns to normal, vital signs return to baseline values
Signs of deterioration: loss of consciousness, breathing unstable, vital signs labile
For patients with cardiovascular diseases and/or diabetes mellitus, start treatment with smaller doses of epinephrine
- Paradoxically, patients taking beta-adrenergic blocking agents may require more epinephrine to reverse the effects of anaphylaxis.

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