Contrast Dye Allergy
Answer: C
This man is having an acute reaction to the radiocontrast medium, of which there are two main types: chemotoxic and hypersensitivity reactions. Chemotoxic (also called physiologic) reactions include vasovagal reactions (vomiting, bradycardia, hypotension), seizures, arrythmias, and end-organ damage (most often acute kidney injury). These reactions are dependent on the dose and timing of the agent; they are most likely due to the hypertonic effects of the agent and subsequent rapid fluid shifts.
Hypersensitivity reactions are idiosyncratic and independent of the dose and infusion rate (reactions may be immediate or delayed several days). Although this is not an allergy-mediated syndrome (no IgE-mediation), the clinical presentation is identical to anaphylaxis, with skin signs, wheezing, stridor, hypotension, and/or mental status changes. As such, hypersensitivity reactions to contrast media should be treated as an anaphylactic/anaphylactoid reaction with epinephrine.
Age and risk factors are not contraindications to receiving epinephrine (B); the possible vasospastic effect is vastly outweighed by the risk of impending cardiovascular collapse: give epinephrine.
It is important to know the route and concentration of epinephrine for treatment of anaphylaxis. By far the most common and safest route is intramuscular (IM): give 0.3 to 0.5 mg IM of the 1:1,000 solution (pediatrics: 0.01 mg/kg 1:1,000 IM up to 0.3 mg IM) (C).
For the patient in cardiovascular collapse or shock IM is still an option. However, if an IV is already established and the patient is in extremis (note: if there is no IV at the time, use IM – do not delay), then the IV formulation of 1:10,000 may be used at 0.1 mg. 1:10,000 IV may be given over 5 minutes. (Just remember: if given IV, the solution must be more dilute – IM needs the more concentrated solution!)
Hypersensitivity reactions are not true anaphylactic reactions, and the patient may receive contrast at some point in the future (A) (there is up to 25% chance of a similar reaction with a subsequent dose – compare that with anaphylaxis, which would be a 100% chance of reaction). These are rare in children. Elective imaging or procedures may be pretreated well before the study. In the emergency department, if the study is necessary, a patient may be pretreated with hydrocortisone (200 mg IV) and diphenhydramine (50 mg IV) immediately prior to the scan. An alternate agent with the lowest osmolality should be used. This is not always practical in the emergency setting, and the emergency physician must weigh the risks, benefits, and patient characteristics in the decision.
Risk factors associated with (not causative of) hypersensitivity reaction to contrast dye include asthma, atopy, and history of multiple allergies. Allergy to seafood and shellfish is not a risk factor (iodine does not cause allergy – the allergy in seafood arises from particular proteins); likewise, allergy to povidone-iodine solution does not convey a higher risk for hypersensitivity to radiocontrast media.
Reference
Cochran ST. Anaphylactoid reactions to radiocontrast media. Curr Allergy Asthma Rep. 2005; 5:28.
Vanden Hoek TL, Morrison LJ, Shuster M, Donnino M, Sinz E, Lavonas EJ, Jeejeebhoy FM, Gabrielli A. Part 12: cardiac arrest in special situations: 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2010;122(suppl 3):S829 –S861
This man is having an acute reaction to the radiocontrast medium, of which there are two main types: chemotoxic and hypersensitivity reactions. Chemotoxic (also called physiologic) reactions include vasovagal reactions (vomiting, bradycardia, hypotension), seizures, arrythmias, and end-organ damage (most often acute kidney injury). These reactions are dependent on the dose and timing of the agent; they are most likely due to the hypertonic effects of the agent and subsequent rapid fluid shifts.
Hypersensitivity reactions are idiosyncratic and independent of the dose and infusion rate (reactions may be immediate or delayed several days). Although this is not an allergy-mediated syndrome (no IgE-mediation), the clinical presentation is identical to anaphylaxis, with skin signs, wheezing, stridor, hypotension, and/or mental status changes. As such, hypersensitivity reactions to contrast media should be treated as an anaphylactic/anaphylactoid reaction with epinephrine.
Age and risk factors are not contraindications to receiving epinephrine (B); the possible vasospastic effect is vastly outweighed by the risk of impending cardiovascular collapse: give epinephrine.
It is important to know the route and concentration of epinephrine for treatment of anaphylaxis. By far the most common and safest route is intramuscular (IM): give 0.3 to 0.5 mg IM of the 1:1,000 solution (pediatrics: 0.01 mg/kg 1:1,000 IM up to 0.3 mg IM) (C).
For the patient in cardiovascular collapse or shock IM is still an option. However, if an IV is already established and the patient is in extremis (note: if there is no IV at the time, use IM – do not delay), then the IV formulation of 1:10,000 may be used at 0.1 mg. 1:10,000 IV may be given over 5 minutes. (Just remember: if given IV, the solution must be more dilute – IM needs the more concentrated solution!)
Hypersensitivity reactions are not true anaphylactic reactions, and the patient may receive contrast at some point in the future (A) (there is up to 25% chance of a similar reaction with a subsequent dose – compare that with anaphylaxis, which would be a 100% chance of reaction). These are rare in children. Elective imaging or procedures may be pretreated well before the study. In the emergency department, if the study is necessary, a patient may be pretreated with hydrocortisone (200 mg IV) and diphenhydramine (50 mg IV) immediately prior to the scan. An alternate agent with the lowest osmolality should be used. This is not always practical in the emergency setting, and the emergency physician must weigh the risks, benefits, and patient characteristics in the decision.
Risk factors associated with (not causative of) hypersensitivity reaction to contrast dye include asthma, atopy, and history of multiple allergies. Allergy to seafood and shellfish is not a risk factor (iodine does not cause allergy – the allergy in seafood arises from particular proteins); likewise, allergy to povidone-iodine solution does not convey a higher risk for hypersensitivity to radiocontrast media.
Reference
Cochran ST. Anaphylactoid reactions to radiocontrast media. Curr Allergy Asthma Rep. 2005; 5:28.
Vanden Hoek TL, Morrison LJ, Shuster M, Donnino M, Sinz E, Lavonas EJ, Jeejeebhoy FM, Gabrielli A. Part 12: cardiac arrest in special situations: 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2010;122(suppl 3):S829 –S861