Anaphylaxis and anaphylactic shockOn January 23, 2019 by Ronald S. White
Anaphylaxis is a severe, potentially life-threatening, generalized or systemic hypersensitivity reaction (allergic or non-allergic). Hypersensitivity is a repetitive, objective and subjective symptom caused by an overreaction of the immune system to a specific stimulus in a dose that is well tolerated by healthy individuals. Anaphylactic shock (the most severe manifestation of anaphylaxis) is a rapidly developing anaphylactic reaction in which a life-threatening decrease in blood pressure occurs.
The main causes of anaphylaxis:
(a) Medicines – most commonly β-lactam antibiotics, myorelaxants, cytostatics, barbiturates, opiates;
b) food – in adults most often fish, seafood, peanuts, citrus fruits, proteins of cow’s milk, chicken eggs and mammal meat;
c) membrane insect poisons;
d) proteins used parenterally – blood, blood components and blood products, hormones (e.g. insulin), enzymes (e.g. streptokinase), serums (e.g. antitetanus), allergens used for diagnosis in vivo and immunotherapy;
e) inhalation allergens – e.g. horse hair;
(a) Direct release of mediators from fat cells – opioids, myorelaxanths, colloidal solutions (e.g. dextran, hydroxyethylecrahmal, human albumin solution) or hypertensive (e.g. mannitol), physical activity;
b) immune complexes – blood, blood components and blood products, immunoglobulins, animal serums and vaccines, dialysis membranes;
c) change in arachidonic acid metabolism – hypersensitivity to acetylsalicylic acid (ASA) and other anti-inflammatory drugs (AIE);
d) anaphylaxis mediators or similar substances in food (histamine, tyramine), too low activity of enzymes that break down anaphylaxis mediators;
e) other or unknown mechanisms – X-ray-contrast drugs, contaminated food and preservatives.
Since immunological mechanisms are not involved in a non-allergic reaction, shock may occur as early as the first contact with this factor. The most common causes of anaphylaxis are drugs, food and insect poisons; in ≈30 % of cases, despite detailed diagnosis, the cause cannot be determined (idiopathic anaphylaxis). Sometimes anaphylaxis requires 2 or more factors (e.g. allergen action and physical activity).
The most frequent mechanism of anaphylaxis is IgE-dependent reaction, non-immunological reactions occur less frequently. A common feature is the degranulation of mast cells and basophils. Released and produced mediators (among them histamine, tryptaza and arachidonic acid metabolites, platelet activation factor, NO) cause smooth muscle contraction in the airways and gastrointestinal tract, expand and increase the permeability of blood vessels, stimulate the end of sensitive nerves, and activate inflammatory cells, complement system, coagulation system and fibrinolysis.
Under their influence is a chemotaxis of eosinophils, which potentiates and prolongs anaphylactic reaction. Increased permeability of blood vessels and rapid movement of fluid into the extravascular space may cause the loss of up to 35% of the effective volume of circulating blood within ≈ 10 min. Episodes of severe anaphylaxis may occur in individuals with defective enzymes metabolizing its mediators, e.g. thrombocyte activation factor acetylhydrolase (severe anaphylaxis episodes on peanuts and insect venom).
CLINICAL PRESENTATION AND NATURAL FLOW
Symptoms of anaphylaxis most often appear within a few seconds to a few minutes after the exposure of the provoke factor (but sometimes later – even up to several hours): upward.
The faster the symptoms develop, the higher the risk of severe and life-threatening anaphylaxis, and initially mild symptoms (e.g. restricted to skin and subcutaneous tissue) may develop rapidly into life-threatening symptoms unless appropriate treatment is applied immediately. There are also late or two-phase reactions, in which the symptoms manifest or intensify again after 8-12 hours. Symptoms of anaphylaxis may persist for several days despite proper treatment, especially if the etiological factor is the food allergen consumed.
Symptoms of anaphylactic shock (regardless of the cause) are cold, pale skin, evaporation, sleeping subcutaneous veins, hypotension, tachycardia, oliguria or anuria, involuntary stools and loss of consciousness. There could be a stop in the circulation.
Based on typical subjective and objective signs and symptoms that develop shortly after contact with a factor capable of causing anaphylactic reactions.
The faster the symptoms develop, the higher the risk of severe and life-threatening anaphylaxis. The determination of tryptase, histamine or methylhistamine is not generally available and is of no practical importance. After 4 weeks from the anaphylaxis episode, a screening is performed to determine the cause of the anaphylaxis; allergen-specific IgE may be useful, while provocative samples should be performed with great care.
In practice, it is important to distinguish anaphylaxis from the most common vasovagal reactions (loss of consciousness). During fainting, skin covers are usually cold and pale, but there is no hives, swelling, itching, bronchial obstruction, nausea, bradycardia occurs instead of tachycardia.