According to Coombs and Gell, allergies are divided into four different types:
- Immediate-type allergic reaction
- Cytotoxic-type allergic reaction
- Immune complex-type allergic reaction
- Delayed-type allergic reaction
Anaphylactic shock belongs to the type 1 hypersensitivity or immediate-type allergic reaction. The most common anaphylactic reactions are caused by:
- Food (including nuts, eggs, soy, etc.)
- Insect bites
- Medication (metamizole, penicillin, NSAR)
- Inhalation of allergens (pollen, latex, etc.)
A “first exposure“ with the antigen occurs prior to an allergic reaction. As a result of initial exposure, the body produces IgE-antibodies, which bind to the surfaces of mast cells and are specific to the sensitizing allergen. The complex immunological reaction then proceeds quickly. Once there is a second exposure to the same or similar allergen, the bound IgE-antibodies interlink with each other and lead to degranulation of mast cells. This leads to the release of inflammatory mediators, especially histamine and prostaglandins, followed by vascular dilatation (which leads to a drop in blood pressure) with an increase in the permeability of the vessels (which leads to swelling).
Anaphylactic shock is the most severe form of the type 1 reaction. This leads to redistribution of blood volume in the peripheral circulation (distributive shock), with reduced venous return and reduced cardiac output. This leads to decreased tissue perfusion and tissue hypoxia.
|Symptoms||The release of histamine causes…|
|Bronchospasm, colic and rhinitis, conjunctivitis, bronchial asthma||Peripheral vasodilation and increased vascular permeability|
|Erythema||Accumulation of blood in the capillary bed|
|Edema, pulmonary edema||Fluid shift into the stroma|
|Flushing, dizziness, exanthema → hypotension, laryngeal edema, bronchospasm with dyspnea, tachycardia, altered mental status → circulatory failure with multiple organ failures!||Hypovolemia, hypoxia, vasodilation|
Acute Therapy of Anaphylaxis
Treatment of anaphylactic shock includes:
- Recognize the condition early (this is critical).
- Remove or discontinue (in the case of medication or other agents) the offending allergen.
- Administer oxygen via face mask.
- Obtain adequate (i.e. large bore) venous access as soon as possible (needed to administer medications).
- Administer corticosteroids (e.g. prednisolone), and H1- and H2- antihistamines intravenously (high doses).
- Administer epinephrine (i.m. or i.v.)- patients may not have easy venous access when in shock.
- Administer crystalloids intravenous crystalloids to maintain volume.
- Administer fast-acting inhaled β2-sympathomimetic.
- Recognize that a GCS- score of < 8 requires endotracheal intubation for airway protection and oxygenation.
In Order to Avoid a Shock…
Desensitization: The specific immunotherapy can be used for prophylactic sensitization to specific allergens, e.g. bee or wasp venom and certain types of pollen. A steady increase of the injected (subcutaneous or sublingual) antigen in minimal dosage can achieve a physiological reaction rather than an excessive IgE-antibody production. Especially younger patients with a monovalent allergy benefit from desensitization therapy.
Emergency-kit: Patients should carry an emergency kit with them at all times and know how and when to administer various medications, including H1-antihistamine, corticosteroids, and epinephrine.
Breast milk diet: reduction of developing atopic predisposition by exclusive breastfeeding during the first 4-6 months of life.
Stimulating climate: in the event of pollen allergies, relocation is an extreme form of prophylaxis.