Anaphylaxis

Anaphylaxis is an acute, life-threatening, IgE-mediated allergic reaction that occurs in previously sensitized patients when they re-meet a familiar antigen. Symptoms include stridor, wheezing, dyspnea and hypotension. The diagnosis is made clinically. Bronchospasm and edema of the upper respiratory tract pose a threat to life and require inhalation or injection of beta-agonists and sometimes endotracheal intubation. Hypotension is stopped by intravenous injection of liquids and vasoconstrictor drugs.

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What causes anaphylaxis?

Usually anaphylaxis is caused by drugs (for example, beta-lactam antibiotics, insulin, streptokinase, allergen extracts), food (nuts, eggs, seafood), proteins (tetanus antitoxin, blood products during blood transfusion), animal toxins, latex. Peanut and latex allergens can be spread by air. A history of atopy does not increase the risk of anaphylaxis, but increases the risk of a fatal outcome if anaphylaxis occurs.

The interaction of antigens with IgE on the surface of basophils or mast cells causes the release of histamine, leukotrienes and other mediators that cause a contraction of smooth muscles (bronchoconstriction, vomiting, diarrhea) and vasodilation with the release of plasma from the bloodstream.

Anaphylactoid reactions are clinically indistinguishable from anaphylaxis, but they are mediated not through IgE and do not require pre-sensitization. Their cause is direct stimulation of mast cells or immune complexes that activate the complement system. Their most frequent triggers are iodine-containing radiographic and radiopaque preparations, aspirin, other NSAIDs, opioids, blood transfusion products, lg, physical activity.

Symptoms of anaphylaxis

The main symptoms of anaphylaxis are associated with skin lesions, upper and lower respiratory tract, cardiovascular system and gastrointestinal tract. One organ system or more may be involved, the symptoms do not necessarily progress, in each patient, manifestations of anaphylaxis upon repeated exposure to an antigen are usually repeated.

• Typical symptoms of anaphylaxis are stridor, wheezing in the lungs, desaturation, respiratory distress, changes in the ECG, cardiovascular collapse, and the clinical picture of shock.
• Less typical symptoms of anaphylaxis are edema, rash, urticaria.

It is necessary to suspect, if in an anamnesis there are similar episodes of severe allergic reactions with respiratory problems and / or hypotension, especially if there were skin manifestations.

Symptoms vary from mild to severe and include fever, itching, sneezing, rhinorrhea, nausea, intestinal cramps, diarrhea, choking or dyspnea, palpitation, dizziness. The main objective signs are lowering of arterial pressure, tachycardia, urticaria, angioedema, dyspnea, cyanosis and fainting. Shock can develop for several minutes, the patient is in a state of inhibition, does not respond to stimuli, death is possible. At a collapse there can be no respiratory and other signs.

The diagnosis of anaphylaxis is put in a punctilious manner. The risk of rapid shock progression does not leave time for research, although mild questionable cases can give time to determine within 24 hours the level of N-methyl histamine in the urine or serum level of tryptase.

What diseases differentiate anaphylaxis?

• Primary disease of the cardiovascular system (for example, congenital heart disease in a newborn).
• Sepsis (with a rash).
• Allergy to latex.
• Stressed pneumothorax.
• Acute severe asthma (history of asthma, with hospitalizations).
• Obstruction of the respiratory tract (for example, aspiration of a foreign body).

Treatment of anaphylaxis

Adrenaline is the basis of treatment and should be administered immediately. This drug is administered subcutaneously or intramuscularly (usual dose 0.3-0.5 ml at 1: 1000 dilution for adults and 0.01 ml / kg for children, reintroduced after 10-30 minutes); maximum absorption is achieved by intramuscular injection. Patients with collapse or severe airway obstruction may be administered adrenalin intravenously at a dose of 3-5 mL at a dilution of 1:10 000 for 5 minutes or dropwise [1 mg per 250 ml of 5% distilled water to reach a concentration of 4 μg / ml, starting at 1 μg / min to 4 μg / min (15-60 ml / h)]. Adrenaline can be administered by sublingual injection (0.5 ml in a 1: 1000 solution) or endotracheally (3 to 5 ml in a 1:10 000 dilution diluted in 10 ml of saline). A second subcutaneous injection of epinephrine may be necessary.

You can use 1 mg of glucagon tablets following infusion at a rate of 1 mg / h in patients receiving oral beta-blockers, which alleviate the effect of epinephrine.

Patients with stridor and shortness of breath, who are not helped by adrenaline, need to give oxygen, and they must be intubated. Early intubation is recommended for the reason that waiting for a response to adrenaline can lead to edema of the airways so severe that endotracheal intubation will become impossible, and cryptothyroidism will be required.

In order to increase blood pressure intravenously inject 1-2 liters (20-40 ml / kg for children) isotonic fluid (0.9% saline solution). Hypotension, refractory to the administration of liquids and intravenous injection of epinephrine, is treated with vasoconstrictive drugs [eg, dopamine 5 μg / (kghmin)].

Antihistamines - and H ₂ -blockers (for example, diphenhydramine 50-100 mg intravenously), and H ₂ -blockers (for example, cimetidine 300 mg intravenously) - should be given every 6 hours until the symptoms come to rest. For relief of bronchoconstriction, inhalation beta-agonists are useful; long-term appoint an inhalant albuterol 5-10 mg. The role of glucocorticoids is not proven, but they can help in preventing late reactions in 4-8 hours; initial dosage of methylprednisolone 125 mg intravenously.

What needs to be done first if there is anaphylaxis?

Oxygen therapy.

Adrenaline slowly intravenously 1 mcg / kg give a fraction under ECG monitoring until the resolution of hypotension (solution 1:10 000):

• 12 years: 50 μg (0.5 ml);
• 6-12 years: 25 μg (0.25 ml);
• > 6 months - 6 years: 12 μg (0.12 ml);
• <6 months: 5 μg (0.05 ml).

If there is no venous access, adrenaline is administered intramuscularly (1: 1000 solution):

• 12 years: 500 μg (0.5 ml);
• 6-12 years: 250 μg (0.25 ml);
• > 6 months - 6 years: 120 μg (0.12 ml);
• <6 months: 50 μg (0.05 ml).

Antihistamine - Chlorphenamine (Chlorpheniramine):

• 12 years: intravenously or intramuscularly 10-20 mg;
• 6-12 years: intravenously or intramuscularly 5-10 mg;
• 1-6 years: intravenously or intramuscularly 2.5-5 mg.

In all cases of severe or recurrent reactions, as well as patients with asthma, administer hydrocortisone intravenously 4 mg / kg:

• 12 years: intramuscularly or slowly intravenously 100-500 mg;
• 6-12 years: intramuscularly or slowly intravenously 100 mg
• 1-6 years: intramuscularly or slowly intravenously 50 mg.

If the clinical picture of shock has not improved under the influence of drug therapy, administer intravenously a liquid of 20 ml / kg body weight. If necessary, you can repeat.

Further management

• If accompanied by severe bronchospasm and there is no response to adrenaline - bronchodilators, for example salbutamol dosing device / inhaler, in accordance with the protocol for acute severe asthma.
• Infusion of catecholamines, as in cardiovascular instability, can last several hours - adrenaline or norepinephrine 0.05-0.1 mcg / kg / min.
• Control of blood gases for the decision to use bicarbonate - up to 1 mmol / kg 8.4% sodium bicarbonate (1 mmol = 1 ml), if the pH is below 7.1.

How is anaphylaxis prevented?

Anaphylaxis is prevented by avoiding contact with known provoking agents. Desensitization is used when it is impossible to avoid contact with allergens (for example, stings of stinging insects). Patients with a late reaction to radiocontrast agents should avoid repeated contact with them; if their use is absolutely necessary, 18 hours before the procedure, prednisolone 50 mg is taken intravenously every 6 hours 3 times and for 1 hour before the procedure, diphenhydramine 50 mg orally; but there is no evidence to support the effectiveness of this approach.

Patients with anaphylactic reaction to the poison of stinging insects, food and other known substances are advised to wear an "anxious" bracelet and carry a syringe with adrenaline (0.3 mg for adults and 0.15 mg for children) to provide self-help after contact with the allergen .