الفهرس 
Immune mechanisms associated with anaphylaxisOnly 14 pages are availabe for public view
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Abstract
damage resulting from prolonged or repeated antigen exposure. These reactions, called hypersensitivity reactions, cause tissue injury by the release of chemical substances that attract and activate cells and molecules resulting in inflammation. These reactions are classified into four hypersensitivity types depending upon the mechanism(s) that underlie the tissue damage. The first three types involve antigen-antibody reactions, while the fourth is antibody-independent, involving cell-mediated immune responses only.
Anesthesiologists administer a diversity of parenteral drugs in the perioperative period, including blood products and drugs, or manage patients during exposure to multiple foreign substances, all of which have the potential to produce a spectrum of adverse reactions. Allergic reactions are one type of an adverse reaction, and the most severe form is anaphylaxis. Unfortunately, patients may not always know they have been sensitized to a drug or protein by previous exposure. Intraoperative anaphylaxis, especially after anesthesia induction, is problematic because the patient is exposed to multiple drugs in an extremely short period— including induction drugs, opioids, antibiotics, and neuromuscular blocking drugs (NMBDs)—and occult antigens such as latex or drug additives/ preservatives. The clinical diagnosis of intraoperative anaphylaxis is problematic because most anesthetics, including propofol, cause vasodilatation, hypotension, and potentially cardiopulmonary dysfunction because of their direct and indirect effects on sympathoadrenergic responses, the heart, and the vasculature. Further, the patient with preexisting cardiovascular disease and hypovolemia may even be more acutely affected by the changes that occur after anesthetic induction.
The overall distribution of the various causal agents is very similar in most reported series. Neuromuscular blocking agents represent the most frequently involved substances with a range of 50–70%, followed by latex (12–16.7%),then followed by antibiotics (15%) .
A careful history regarding adverse drug reactions and allergies should be conducted before any surgical procedures requiring anesthesia. Identification of at risk patients will lead to avoidance of a particular drug and is likely to prevent anaphylaxis. Atopic individuals with increased IgE are at risk for allergic reactions to propofol and latex Health-care workers and patients with multiple prior surgical procedures can be sensitized to latex and may develop anaphylaxis when exposed to latex.
Patients with anaphylaxis who have no alternative drug available can be desensitized. Eligible reactions are usually due to the paraaminobenzoic acid metabolite from esters or methylparaben (a preservative) Epinephrine and metabisulfite, often present in local anesthetics, can also cause adverse drug reactions. Vasovagal responses, tachycardia, lightheadedness, metallic taste, and perioral numbness can result from intravascular injection of the local anesthetic, epinephrine or both. The most common immune-mediated reaction to local anesthetics is a delayed hypersensitivity reaction (Type IV reaction), or contact dermatitis. Skin and challenge tests are used for diagnosis, and it is important to use preservative-free local anesthetics. There is no cross-reactivity between amide and ester local anesthetics, except in cases in which a preservative is the allergen. Although cross-reactivity occurs among esters, it is very unusual among amides.
Anaphylaxis is the maximal variant of an acute life-threatening immediate-type allergy. Due to its often dramatic onset and clinical course, practical knowledge in the management of these reactions is mandatory both for physicians and patients. It has to be distinguished between acute treatment modalities and general recommendations for management of patients who have suffered from an anaphylactic reaction. Acute treatment comprises general procedures like positioning, applying an intravenous catheter, call for help, comfort of the patient as well as the application of medication. The acute treatment modalities are selected depending upon the intensity of the clinical symptomatology as they are categorized in ‘severity grades’. First of all it is important to diagnose anaphylaxis early and consider several differential diagnoses. This diagnosis is purely clinical and laboratory tests are of no help in the acute situation. Epinephrine is the essential antianaphylactic drug in the pharmacologic treatment. Furthermore, glucocorticosteroids are given in order to prevent protracted or biphasic courses of anaphylaxis; they are of little help in the acute treatment. Histamine H1-antagonists are valuable in mild anaphylactic reactions; they should be given intravenously if possible. The replacement of volume is crucial in antianaphylactic treatment. Crystalloids can be used in the beginning, in severe shock colloid volume substitutes have to be applied. Patients suffering from an anaphylactic episode should be observed over a period of 4–10 h according to the severity of the symptomatology. It is crucial to be aware or recognize risk patients as for example patients with severe uncontrolled asthma, or under β-adrenergic blockade. When bronchial symptoms are in the focus, inhaled β2-agonists can be tried, also for laryngeal edema. The use of combined H1- and H2-antagonists has been recommended for prophylaxis prior to application of potentially anaphylaxis-eliciting drugs (e.g. radiographic contrast media). Patients who have survived an anaphylactic reaction have to be thoroughly examined and an allergy diagnosis has to be performed with regard to the eliciting agent and the pathogenic mechanism involved. Furthermore, patients should be trained with regard to the nature of anaphylaxis, the major eliciting agents and the principles of behavior and coping with the situation including the handling of epinephrine autoinjectors and the application of antianaphylactic medication. Educational programs for anaphylaxis have been developed.