Allergy to radiopaque substances

With the use of modern radiopaque substances (RVC), the overall incidence of intolerance reactions is 5-8%. They can be divided into two groups: allergic and chemotactic. Chemotactic reactions are due to the physical properties of RVR (osmolarity, viscosity, ability to bind blood calcium) and, as a rule, are clinically manifested by hypotension, bradyarrhythmia and development of stagnation in the lungs. The allergy to radiopaque substances is associated with the response of various parts of the patient's immune system to the chemical structure of the RVC and includes a diverse range of clinical conditions, from minor to fatal.

In the general population, the frequency of allergy to radiopaque substances is about 1%. Severe allergic reactions rarely develop - in 0.1% of patients.

[1], [2], [3]

Why does the allergy to radiopaque substances develop?

The main mechanism of allergy to radiopaque substances is the degranulation of basophils and mast cells due to direct activation of the complement system. Release of granules of histamine and other active substances causes clinical manifestations of allergy (cough, sneezing, bronchospasm, rash and in severe cases - collapse due to excessive systemic vasodilation). Any patient with developed hypotension during PCI or CAG should be excluded from a severe allergic reaction. Differential diagnosis should be carried out with vasovagal reactions. A distinctive feature of the allergic reaction is the development of tachycardia, which, however, may be absent in patients receiving beta-blockers or with an implanted pacemaker.

Most allergic reactions occur within the first 20 minutes after exposure to the RVC. A serious or fatal allergic reaction in 64% of cases develops earlier - in the first 5 minutes after contact. Severe allergic reactions can begin as minor, followed by rapid progression within a few minutes. There are two categories of patients with an increased risk of developing an allergic reaction to RVC. If the patient has already had an allergy to radiopaque substances, then with its subsequent introduction, the risk of its development increases to 15-35%. The second group at risk consists of patients with atopic diseases, asthma and penicillin allergy. The risk of developing an allergic reaction in these patients increases by a factor of 2. There are indications for an increased risk in patients with allergy to molluscs and other seafoods in the anamnesis.

Symptoms of allergy to radiopaque substances

Allergic reactions include a wide range of clinical manifestations - from the lungs (in the form of itching and local urticaria) to severe (shock, respiratory arrest, asystole).

Classification of severity of allergy to radiopaque substances

Lightweight	Moderate Gravity	Heavy
Limited urticaria Itching Erythema	Diffusive urticaria Edema Kiinke Edema of the larynx Bronchospasm	Shock Breath stop Heart stop

Treatment of allergies to radiopaque substances

In the treatment of an allergic reaction to the introduction of PKV, 5 classes of pharmacological agents are used: H1-blockers, H2 blockers, corticosteroids, epinephrine and saline. The tactics of treatment depend on the severity of the allergic reaction and the patient's condition. At a mild degree (a urticaria, an itch) apply diphenhydramine in a dose of 25-50 mg intravenously. If there is no effect, adrenaline is injected subcutaneously (0.3 ml of the solution at a dilution of 1: 1000 every 15 minutes to a dose of 1 ml). In this case, you can additionally enter within 15 minutes diluted in 20 ml of physiological solution of cimetidine at a dose of 300 mg IV or ranitidine at a dose of 50 mg IV.

With the development of bronchospasm, the following sequence of actions is recommended:

• oxygen through a mask, oximetry;
• with mild degree - inhalation of albuterol; at an average degree - adrenaline subcutaneously (0.3 ml of the solution at a dilution of 1: 1000 every 15 minutes to a dose of 1 ml); when severe - adrenaline 10 μg intravenously bolus for a minute, then infusion of 1-4 μg / min (under the control of blood pressure and ECG);
• Diphenhydramine 50 mg intravenously;
• hydrocortisone 200-400 mg intravenously;
• H2-blocker.

When swelling of the face and larynx:

• call of resuscitator;
• assessment of airway patency:
  • additional oxygen through the mask;
  • intubation;
  • preparation of a set for tracheostomy;
• in more mild cases, epinephrine subcutaneously (0.3 ml of the dilution solution 1: 1000 every 15 minutes to a dose of 1 ml), with an average severity and severe reaction - adrenaline intravenously bolus 10 μg for 1 min, then infusion 1-4 μg / min (under the control of blood pressure and ECG);
• Diphenhydramine 50 mg intravenously;
• oximetry;
• H2-blocker.

With hypotension and shock:

• simultaneously - intravenously adrenaline bolus 10 μg every minute until an acceptable level of blood pressure, then infusion of 1-4 μg / mip + large volumes of isotonic solution (up to 1-3 liters in the first hour);
• additional oxygen through a mask or intubation;
• Diphenhydramine 50-100 mg intravenously;
• hydrocortisone 400 mg intravenously;
• central venous pressure control;
• oximetry. When ineffective:
• intravenously dopamine at a rate of 2-15 μg / kg / min;
• H2-blocker;
• resuscitation measures.

Prevention of allergy to radiopaque substances

The basis for the prevention of allergic reaction to RVB is premedication with a combination of corticosteroids and H1-blockers. A number of studies have shown the benefits of adding H2-blockers, which are believed to further block the IgE-mediated component of the allergic reaction. There are several schemes for the prevention of allergic reactions, in which different doses and routes of administration of the drugs of these groups are used. The most demonstrative basis is the following scheme: taking prednisolone 50 mg orally for 13, 7 and 1 h before the procedure (150 mg total) + taking 50 mg of diphenhydramine orally for 1 hour before the procedure. In one study, the use of this regimen in patients with an indication of a previous allergy to radiopaque substances reduced the overall frequency of a repeated allergic reaction to 11%. In this case, hypotension developed in only 0.7% of patients. The simpler scheme is more often used: reception of prednisolone inside in a dose of 60 mg in the evening before the procedure, and in the morning on the day of the procedure the intake of prednisolone inside 60 mg + 50 mg of diphenhydramine. There is also an alternative scheme: taking 40 mg of prednisolone every 6 hours for 24 hours + diphenhydramine 50 mg intravenously + cimetidine 300 mg intravenously once.

In the presence of an allergic reaction to the ionic RKV, if necessary, a non-ionic RVB should be used in the subsequent re-procedure, since the risk of a severe cross-allergic reaction in this case is less than 1%.