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Allergy in anaesthesia

Created: 20/2/2008
Updated: 9/10/2008
 

Allergy in anaesthesia

Classification of immunological reactions

They are classified into four types based on the antibody involved and have the following characteristics:

Reaction

Antibody involved

Chemical mechanism

Example

Type I

(Immediate hypersensitivity)

IgE

Antigen + IgE (on mast cells and basophils) → mast cell product release

Anaphylaxis

Cutaneous wheal and flare

Type II

(Cytotoxic)

IgG, IgM

IgG, IgM + antigen on cell membranes → complement activation → release of anaphylotoxins and cell destruction

Transfusion reactions

Haemolytic anaemia

Rh incompatibility

Type III

(Immune complex)

IgG, IgM

IgG, IgM + antigen (fluid phase) → deposition in blood vessels → complement activation + cell destruction

Serum sickness

Glomerulonephritis

Type IV

(Delayed hypersensitivity)

(cell-mediated)

Sensitised lymphocytes + antigen → release of lymphokines

Contact dermatitis

Antigens and antibodies

Antigens are molecules capable of stimulating an immunological response when injected and antibodies are large protein molecules that are capable of binding to antigens. An important characteristic of this response is specificity (unique antibodies are produced against specific chemical structural antigens).

Antigens may be:

1. Complete antigens (e.g. protamine, streptokinase, insulin)

2. Haptens (e.g. penicillin, thiobarbiturates, sulpha drugs etc.). These are smaller molecules which become antigenic after binding to larger molecules.

Antibodies are protein molecules and have the unique ability to bind to the antigens which stimulated their production. Immunoglobulins are proteins with specific structures that function as antibodies. All antibodies are immunoglobulins, but not all immunoglobulins have antibody function.

Nomenclature

The European task force set up by the Association of Allergists and Immunologists issued a revised nomenclature in 2001. They classified anaphylaxis into allergic and non-allergic anaphylaxis. Allergic anaphylaxis may be both IgE mediated or non-IgE mediated. The older, traditional classification into anaphylactic (immune, IgE-mediated) and anaphylactoid (non-immune) reactions is no longer followed. The task force recommended that the term ‘anaphylactoid’ should no longer be used.

The term ‘anaphylaxis’ stems from the Greek words ‘ana’, meaning against and ’phylaxis’ meaning protection (opposite of prophylaxis). It was first reported by Charles Richet and Paul Portier in 1902. The following resource will deal with anaphylaxis, which is the most serious form of reaction, and clinically the most important for anaesthetists.

Anaphylaxis is a life-threatening immediate hypersensitivity reaction which presents as upper airway obstruction, dyspnoea, syncope and/or hypotension. This complex of physiological changes involving the cardiovascular, respiratory and cutaneous systems is caused by an allergic reaction. An allergic reaction is caused by immunological mechanisms, in contrast to reactions that mimic allergy (drug idiosyncrasies, direct toxicity, drug interactions or overdosage).


ArticleDate:20080220
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