Complications of Contrast Media

Introduction

Contrast media (CM) are an essential aid in diagnostic medical imaging. They are used primarily to enhance the visibility of blood vessels, organs, and pathology in the body. CM are considered pharmacologic agents, and, like any other medication, they are not without adverse effects.

Incidence

Scant data are available regarding the incidence of contrast reactions in children for at least three reasons: (1) few clinical trials with children as subjects have been performed to obtain federal approval of an agent ; (2) assessing symptoms, particularly mild ones in very young children, is difficult; and (3) differentiating true contrast reactions from symptoms is difficult because of sedation, synchronous medications, anxiety, and other preexisting diseases.

In children, use of any intravenous (IV) CM is discriminative and exclusive. Administration of nonionic iodinated contrast is associated with a low incidence of adverse effects. Dillman et al. reported a 0.18% incidence of acute allergic-like reactions to IV administration of nonionic iodinated CM in children, similar to 0.23% reported in the adult population. Most of the contrast reactions are mild in both children and adults. Of all the reported allergic reactions in children, 15% (<0.03% overall) were severe in degree. Fatal reactions are very rare, suggesting the effectiveness of aggressive preventive measures and advancement in management of these reactions.

Gadolinium-based contrast media (GBCM) demonstrate a better safety profile with a lower incidence of allergic-like reactions of 0.04%.

Risk Factors

As with adults, children need to be appropriately screened before CM are administered. Screening includes a complete and specific history from the accompanying adults. Attempts should be made to identify any variables that may preclude the use of the CM or potentially increase the eventuality of an adverse reaction. Factors that may increase this risk include the following:

• 1.

  Known prior reaction to CM.

• 2.

  Known allergies to food products or medications; minor allergies do not pose a significant risk, but a prior anaphylactic reaction to any substance should heighten awareness of the possibility of a similar reaction to CM administration.

• 3.

  A history of asthma.

• 4.

  Known renal disease; renal function in such patients can worsen after administration of CM.

• 5.

  Known heart disease, sickle cell disease, or diabetes mellitus.

Other disease entities, such as pheochromocytoma, dehydration, heart failure, severe hyperthyroidism, and β-blocker therapy, that are known risk factors in adults have not been studied in the pediatric population ( Box 3.1 ).

Pathogenesis

The exact pathogenesis of untoward events after the administration of CM remains obscure and poorly understood. Most of the symptoms resemble an allergic or anaphylactoid reaction to a medication or allergen. However, definitive evidence is lacking that these reactions are truly allergic reactions because antibodies and the typical allergic cascade to these agents have not been identified.

Classification of Allergic-Like Contrast Reactions

Based on severity, contrast reactions can be classified as mild, moderate, or severe. Flushing and a sensation of warmth are considered physiologic responses ( Box 3.2 ).

Mild reactions are usually of short duration and resolve without the need for any treatment. However, patients should be carefully observed until the symptoms resolve because the symptoms could progress to more severe reactions.

Moderate reactions require some form of treatment. More important, close observation is essential until the symptoms resolve. Vital signs should be monitored and IV access should be secured.

Severe reactions, which are rare, can be life threatening. They could present a worsening of mild or moderate reactions. Prompt and aggressive treatment may be required. The assistance of a rapid response or code team often may be necessary.

Management

In the event of any adverse reaction to CM, the IV contrast injection should be discontinued. All reactions and management of the reactions should be documented in the patient care notes, and notation of a contrast allergy should become part of the patient's permanent medical record. The following protocols closely follow the American College of Radiology (ACR) guidelines for management of acute reactions in children. The specific agents used in the management of an adverse reaction are determined by individual institutional pharmacy formulary and policy. Some institutions require the radiology personnel to call for assistance (e.g., a rapid response team) if they administer IV epinephrine for the management of these adverse reactions (given the rare incidence of these events and hence the lack of uniformity in preparedness for these reactions). To be prepared for such reactions, weight-based dosages of the medications used for management should be posted in clearly visible areas where CM are administered to children. Regular review of treatment protocols and practice of contrast reaction scenarios should be performed by radiologists and staff. If at any time a patient does not respond to treatment or the situation seems concerning, it is appropriate to seek additional medical support immediately. This support may be sought from another radiologist in the department or through activation of an institutional rapid response or code team.

Urticaria

Urticaria, the most common reaction to CM, is limited to skin and subcutaneous tissue. Worsening of symptoms can be caused by the accompanying pruritus. Findings on physical examination include the following:

• Red raised wheals that blanch with pressure

• Patchy, symmetric involvement

• Itching, often intense

• Stable vital signs

Mild urticaria is usually self-limiting and does not require treatment.

Close observation for 30 to 60 minutes, or until resolution, is recommended because urticaria may progress to a moderate reaction. Medications may include H ₁ -receptor blockers (such as diphenhydramine) or α-agonists (such as epinephrine). The accompanying parents/responsible adults should be cautioned about the possibility of drowsiness when diphenhydramine is administered. If urticaria is extensive, pay close attention to the patient's blood pressure and watch for signs and symptoms of hypotension, especially orthostatic hypotension.