Vasovagal Reactions Do Not Preclude Further Use of the Contrast: slowing the infusion rate may be sufficient
Atropine (see Atropine, [[Atropine]]): may be required for symptomatic bradycardia
Immediate Hypersensitivity Reaction
Epidemiology
Age: most commonly seen in patients 20-50 y/o
Immediate hypersensitivity reactions are uncommon in children
Relationship to Osmolality: the osmolality of the contrast is the characteristic most strongly associated with the risk of immediate hypersensitivity reaction
Mild-Moderate Immediate Hypersensitivity Reaction: occurs in 5-13% of ionic high osmolality agents, but only in 0.2-3% of non-ionic low osmolality agent
Relationship to First Exposure: approximately 33% of immediate hypersensitivity reactions occur on first exposure to the contrast agent
Idiosyncratic and Independent of Dose/Infusion Rate: immediate hypersensitivity reactions may occur with even small amounts of contrast [MEDLINE]
Onset: develop within 1 hr after contrast administration (usually within 5 min)
Relationship to Seafood/Shellfish Allergy: seafood/shellfish allergy is not an independent risk for factor contrast-induced immediate hypersensitivity (this is a common misperception)
Risk Factors for Immediate Hypersensitivity Reaction
Allergic Disease
Allergic Rhinitis (see Allergic Rhinitis, [[Allergic Rhinitis]]): atopy clearly increases the risk of immediate hypersensitivity reaction to contrast
Asthma (see Asthma, [[Asthma]]): inconsistent risk factor in studies
Atopic Dermatitis (Eczema) (see Atopic Dermatitis, [[Atopic Dermatitis]]): atopy clearly increases the risk of immediate hypersensitivity reaction to contrast
Food Allergy (see Food Allergy, [[Food Allergy]]): atopy clearly increases the risk of immediate hypersensitivity reaction to contrast
Prior Immediate Hypersensitivity Reaction to Radiographic Contrast
Repeated Exposure to Radiographic Contrast Increases the Risk of Both an Immediate Hypersensitivity Reaction and a Severe Immediate Hypersensitivity Reaction
Contrast-specific IgE antibodies have been demonstrated in several studies (Am J Roentgenol, 2008) [MEDLINE] (Allerg Immunol, 1993; Paris) [MEDLINE]
Non-IgE-Mediated: most cases
Activation of Coagulation/Kinin/Complement Cascades
Direct Mast Cell Activation
Inhibition of Cholinesterase
Inhibition of Platelet Aggregation with Increased Serotonin Release
Diagnosis
Serum Tryptase: may be detectable for several hours after immediate hypersensitivity reaction (although elevations are best detected between 30 min-3 hrs after the event)
Half-Life of Serum Tryptase: 90 min
However, a normal serum tryptase level does not exclude the diagnosis of anaphylaxis
Sinus Tachycardia (see Sinus Tachycardia, [[Sinus Tachycardia]]): usually assists in differentiation from vasovagal episode (where bradycardia is more commonly observed)
Use of Low Osmolality Contrast for All Intravascular Procedures: common practice in most settings
Use of Non-Ionic Low Osmolality Contrast in Patients with Prior Serious Allergic Reaction to Materials Other Than Radiographic Contrast, Patients Receiving Contrast by Power Injector, and Possibility of Increased Risk for Immediate Hypersensitivity Contrast Reaction
Premedication for Patients without Prior Contrast Reaction
Provided that a non-ionic low osmolality agent is used, administration of premedication in patients without prior contrast reaction is not supported by the evidence
Extravascular procedures (cystogram, etc) do not require premedication, due to lower risk of immediate hypersensitivity reaction
Premedication for Patients with Prior Contrast Reaction: indicated
Diphenhydramine (Benadryl) (see Diphenhydramine, [[Diphenhydramine]]): administer 1 hr (PO or IV) before procedure
Methylprednisolone (Solumedrol) (see Methylprednisolone, [[Methylprednisolone]]): may be used instead of prednisone at same time intervals
Prednisone (see Prednisone, [[Prednisone]]): administer 50 mg 13 hrs, 50 mg 7hrs, and 50 mg 1hr prior to procedure
Treatment
Discontinue Contrast Administration: do not restart contrast if immediate hypersensitivity reaction is suspected (even if symptoms rapidly resolve)
Treatment of Anaphylaxis (see Anaphylaxis, [[Anaphylaxis]]): standard treatment
Corticosteroids (see Corticosteroids, [[Corticosteroids]]): although commonly used, they do impact acute symptoms, but may be beneficial in preventing/decreasing severity of the delayed symptoms (although data is lacking)
Prognosis
Mortality Rate: age-related -> higher mortality rates in older patients
Delayed Hypersensitivity Reaction
Epidemiology
Onset: develop within 1 hr-several days after contrast administration
Physiology: delayed hypersensitivity reactions are idiosyncratic and independent of dose and infusion rate [MEDLINE]
Radiographic Contrast-Induced Leukostasis with Acute Respiratory Distress Syndrome (ARDS) (see Leukostasis, [[Leukostasis]] and Acute Respiratory Distress Syndrome, [[Acute Respiratory Distress Syndrome]])
Epidemiology: reported with diatrizoate
Physiology: complement activation with generation of C5a -> granulocyte aggregation and adherence to endothelium -> granulocytes obstruct pulmonary capillaries and arterioles and release proteases and oxygen radicals -> endothelial damage and capillary leak syndrome
Increased plasma histamine levels
Clinical: dyspnea and hypoxemia begin within minutes-1 hr of contrast injection
Treatment: corticosteroids may be effective (see Corticosteroids, [[Corticosteroids]])
Fatal complement-induced leukostasis after diatrizoate injection. Principles of clinicopathologic diagnosis. JAMA. 1983 Nov 4;250(17):2340-2 [MEDLINE]
Ionic versus nonionic contrast media: a prospective study of the effect of rapid bolus injection on nausea and anaphylactoid reactions. J Comput Assist Tomogr. 1998;22(3):341 [MEDLINE]
