52: Allergic Reactions

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CHAPTER 52 Allergic Reactions

James Duke, MD, MBA

1 Review the four types of immune-mediated allergic reactions and their mechanisms

image Type I, or immediate hypersensitivity, is immunoglobulin (Ig) E–mediated hypersensitivity and in its most severe form results in anaphylaxis. Usually there is a previous exposure to the antigen during which IgE is produced and binds to mast cells and basophils. After reexposure the antigen cross-links two IgE receptors, initiating the cascade that ultimately results in release of potent vasodilating mediators. Type I reactions will be discussed in greater detail subsequently.
image Type II reactions involve IgG, IgM, and the complement cascade to mediate cytotoxicity; an example is Goodpasture’s syndrome.
image Type III reactions are the result of immune-complex formation, and their deposition in tissue leads to tissue damage; an example is hypersensitivity pneumonitis.
image Type IV reactions, or delayed hypersensitivity, are mediated by T lymphocytes; the best example is contact dermatitis.

2 What is meant by anaphylaxis?

Anaphylaxis is an unanticipated and severe allergic reaction with numerous clinical manifestations, including the following:

image Hypotension, tachycardia, and cardiovascular collapse
image Bronchospasm
image Cutaneous symptoms, including flushing, urticaria, and angioedema
image Gastrointestinal symptoms, including abdominal pain, nausea and vomiting, and diarrhea

Because surgical patients are under drapes, the usual presenting features intraoperatively are hypotension, tachycardia, and bronchospasm. Since these are not uncommon problems encountered by anesthesiologists, a degree of clinical acumen is necessary to arrive at the diagnosis of anaphylaxis and quickly institute therapy.

3 What is an anaphylactoid reaction?

Although the symptoms are indistinguishable from anaphylaxis, an anaphylactoid reaction is nonimmune mediated. Release of inflammatory mediators from mast cells and basophils results in activation of the complement cascade.

4 What are the common causes of anaphylaxis in the operating room?

About 80% of all anaphylactic reactions are caused by either muscle relaxants (e.g., succinylcholine, rocuronium, and atracurium) or latex exposure, but there are other causes:

image Antibiotics, usually penicillin and other β-lactam antibiotics (cephalosporins) (see Question 6).
image Propofol and thiopental: The incidence of allergic reaction to the most current preparation of propofol is estimated to be 1:60,000 administrations; current evidence also suggests that egg-allergic patients are not at increased risk for allergic reactions. The incidence of anaphylaxis is 1:30,000 administrations and may be caused by the presence of sulfur in the compound. No allergic reactions to methohexital have ever been reported.
image Colloids: Dextran and gelatin have an allergic reaction incidence of about 0.3%. Hetastarch is the safest colloid.
image Morphine and meperidine: More than likely the reaction seen is to the result of nonimmunologic histamine release.
image Aprotinin, heparin, and protamine: Allergic reactions to aprotinin occur in <1% of patients, but reexposure increases the risk. Allergic reactions to unfractionated heparin are rare and to low-molecular-weight heparin are even rarer. The most common reaction to heparin is heparin-induced thrombocytopenia (HIT), which is nonimmunologic in origin. Patients with prior exposure to protamine such as those taking neutral protamine Hagedorn (NPH) insulin have the greatest risk of allergic reaction, about 0.4% to 0.76%.
image Local anesthetics: Allergies to local anesthetics with amide linkages (e.g., bupivacaine, lidocaine, mepivacaine, ropivacaine) are extremely rare. True allergic reactions to local anesthetics with ester linkages (e.g., procaine, chloroprocaine, tetracaine, benzocaine) are also rare and may be caused by a para-aminobenzoic acid metabolite. Methylparaben, a preservative in local anesthetics, may cause allergic reactions.

5 Review the issues concerning allergic reactions to muscle relaxants

About 70% of all intraoperative anaphylactic reactions are associated with relaxants. IgE immunoglobulins are sensitive to the tertiary or quaternary ammonium groups found in these compounds. Since such chemical groups are commonly found in foods, cosmetics, and over-the-counter medications, prior exposure to muscle relaxants is often unnecessary. Succinylcholine is more likely to result in anaphylaxis than nondepolarizing relaxants because its smaller, flexible molecular structure can more easily cross-link mast cell IgE receptors. Benzylisoquinolium relaxants are more likely to result in anaphylaxis than aminosteroid relaxants, and benzylisoquinolium relaxants can also cause nonimmunologic histamine release.

6 Should a penicillin-allergic patient receive cephalosporins?

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