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Reaction types

Adverse reactions

• Allergy-like reactions: do not occur from IgE mediated process, but result in histamine release, not dose dependent
• Physiologic reactions: due to specific reaction to contrast, dose dependent
• Many reactions appear to be fear/anxiety related
• Assess appearance, ability to speak, vitals
• Delayed reaction: can occur 3hr-7d after contrast, usually rash +/- itching
• Shellfish allergy: unrelated to iodine, therefore no increased risk of contrast reaction

Mild contrast reaction

• Treatment: usually need observation only, but wait 20-30min in case reaction worsens, may require benadryl PO/IV/IM (1-2mg/kg up to 50mg)
• Anxiety: can give chlorpheniramine 4-10mg PO/IV/IM or diazepam 5mg
• Bronchospasm: can give O₂ 6-10L/min and B-agonist inhaler 90mg/puff x2 puffs for x3 cycles total

Moderate contrast reaction

• Occur in 0.5-2%
• Treatment: hydrocortisone 100-500mg IM/IV, B-agonist inhaler 90mg/puff x2-3puffs repeat PRN
• Bronchospasm: O₂ 6-10L/min and B-agonist inhaler 90mg/puff x2 puffs for x3 cycles total

Severe contrast reaction

• Occur in 0.1%
• Treatment: give epinephrine for bronchospasms +/- laryngospasms, no benefit to antihistamines
• Epinephrine IV: 0.01mg/kg (0.1mL/kg of 1:10K dilution), repeat q5-15min, max single dose 1.0mL (0.1mg), max total dose 1mg
• Epinephrine IM: 0.01mg/kg (0.01mL/kg of 1:1K dilution), maximum 0.15mg < 30kg or 0.30mg > 30kg, inject into lateral thigh, repeat q5-15min, total dose 1mg
• Hypotension: give multiple liters IV fluids, dopamine 2-10ug/kg/min if IVF unsuccessful

Reaction Prevention and Nephropathy

Premedication regimens

• Premedication lowers but does not elimate contrast reaction risk
• Extravascular (GU imaging) contrast reactions are rare, consider premedication for patients with history severe reactions
• Option #1: prednisone 50mg PO 13hr, 7hr, and 1hr before contrast injection + diphenhydramine (benadryl) 50mg IV/IM/PO 1hr before contrast injection
• Option #2: methylprednisolone 32mg PO 12hr and 2hr before contrast injection + diphenhydramine (benadryl) 50mg IV/IM/PO 1hr before contrast injection
• Emergency: hydrocortisone 200mg IV or methyprednisolone 40mg IV q4hr until contrast administration + diphenhydramine (benadryl) 50mg IV/IM/PO 1hr before contrast administration

Contrast nephropathy (CT contrast)

• Unclear how real this reaction is and long-term effects on renal function
• Risk factors: preexisting CKD, DM, dehydration, diuretic use, older age, multiple contrast doses
• Renal function: no clear cutoff, may be Cr > 1.5-2.0 or eGFR < 30-45
• Metformin: contrast administration can cause drug accumulation and lead to biguanide lactic acidosis (50% mortality), discontinue metformin for 48hr after contrast if patient has CKD (eGFR < 30)
• Potential prevention: avoid NSAIDs 2-3d prior, avoid ACEi and diuretics 24hr prior, consider hydration starting 6-12hr prior and continuing for 4-12hr afterwards, consider acetylcysteine 600mg BID day before and day of contrast