An allergic reaction is a reaction that occurs when an immunized organism is stimulated by the same substance again. The reaction is characterized by rapid onset, strong reaction, and rapid fading; it usually does not destroy tissue cells or cause tissue damage, and has obvious genetic tendency and individual differences. Allergic reaction is a kind of immune dysfunction, which refers to a group of clinical symptoms caused by the release of a large amount of allergic mediators by mast cells and basophils after the combination of foreign antigenic substances and specific antibodies in the body, mainly manifested by local vasodilation, increased vascular permeability, contraction of organ smooth muscle and enhanced glandular secretion.
Mechanism of occurrence.
The mechanism of allergic reactions is a complex and abstract process, and the mechanism of type I allergic reactions is divided into three stages.
1, the sensitization phase: allergens into the body can be selected to induce allergen-specific B cells to produce antibody responses, such antibodies and mast cells and basophils (i.e., the textbook of the skin, respiratory or digestive tract mucosa and certain cells in the blood, where mast cells are distributed in the connective tissue around the small subcutaneous vessels and the submucosa, while basophils are mainly distributed in the peripheral blood) of the The allergic state of the body is caused by the binding of mast cells to the surface of the allergen. Usually this sensitized state can be maintained for several months or longer, but if the allergen is not exposed for a long time, the sensitized state can gradually disappear by itself.
2, the excitation phase: refers to the same allergen re-entered the body, through the specific binding of antibodies to the surface of the sensitized mast cells and basophils, so that this cell release bioactive media stage. In this stage, the released bioactive mediators can be prostaglandin D, leukotrienes, platelet activating factor, etc. in addition to histamine, but they all have similar effects and can cause smooth muscle contraction, capillary dilation and permeability enhancement, and increased glandular secretion.
3, the effect stage: refers to the biological active media effect on the effect tissue and organs, causing local or systemic allergic reaction stage. According to the occurrence and duration of the reaction, it can be divided into two types: early phase reaction and late phase reaction. Early phase reactions are mainly caused by histamine, which usually occurs within seconds of contact with the allergen and can last for several hours, while late phase reactions are caused by leukotrienes and platelet-activating factors, which occur 6 to 12 hours after allergen stimulation and can last for several days.
The reaction occurs 6 to 12 h after allergen stimulation and can last for several days.
Clinical manifestations.
1. Anaphylaxis reactions.
(1) Respiratory obstruction symptoms: caused by laryngeal edema, tracheal and bronchial spasm and pulmonary edema. The manifestations are chest tightness, palpitations, blocking sensation in the larynx, dyspnea and flushing, etc., accompanied by a sense of imminence, dry mouth, dizziness, facial and limb numbness.
(2) Symptoms of microcirculatory disorders: caused by extensive dilation of microvessels. They are manifested as pallor, irritability, chill, cold sweat, weak pulse and decreased blood pressure, etc.
(3) Central nervous system symptoms: caused by hypoxia in the brain. They are loss of consciousness, coma, convulsions and urinary and fecal incontinence.
(4) Allergic skin reactions: such as pruritus, urticaria and other kinds of rashes, etc.
(2) Hematologic-like reactions: The distinction between the types of reactions in this group mainly depends on the changes in blood tests. The main symptoms are: granulocytopenia or deficiency, thrombocytopenia, aplastic anemia, hemolytic anemia and megaloblastic anemia, etc.
3.Seropathy-like reaction. The reaction symptoms are mainly serum sickness-like changes, with sudden and widespread erythema and urticaria-like rash common, and may be accompanied by fever, arthralgia and lymph enlargement.
4.Other systemic reactions. Most of the skin and mucous membrane rashes caused by drugs belong to this type. Clinical manifestations are diverse, common allergic drug rash are: fixed drug rash, epidermolysis bullosa, exfoliative dermatitis type drug rash, eczema dermatitis type drug rash, erythema multiforme and severe erythema multiforme drug rash, photosensitive drug rash, etc.
Anaphylaxis emergency plan
1.Once anaphylaxis occurs, immediately stop using the drug that causes allergy, resuscitate the patient in place, and quickly report to the doctor.
2. Immediately lie down and inject epinephrine 1mg subcutaneously as prescribed by the doctor, or less for children. If symptoms are not relieved, inject 0.5ml subcutaneously or intravenously every 30min until out of danger, pay attention to keep warm.
3.Improve the symptoms of hypoxia, give oxygen inhalation, and give artificial respiration if respiratory depression occurs. If laryngeal edema affects breathing, tracheal intubation should be prepared immediately and tracheotomy should be performed if necessary.
4, quickly establish intravenous access, replenish blood volume, if necessary, establish two intravenous access. Apply crystalloids and antihypertensive drugs to maintain blood pressure, apply aminophylline to relieve bronchospasm, and give respiratory stimulants, in addition to antihistamine and corticosteroids.
5.In case of cardiac arrest, immediately perform chest compressions, artificial respiration and other cardiopulmonary resuscitation measures.
6.Observation and recording, closely observe the patient’s consciousness, temperature, pulse, respiration, blood pressure, urine output and other clinical changes, and do not move the patient before he/she is out of danger.
7.Record the resuscitation process timely and accurately within 6 h according to the Regulations on the Treatment of Medical Accidents.