Pre-Medication for Allergy
Our recommendations are taken from the ACR contrast manual (can be viewed by clicking here). The patients who primarily receive premedication are those who have had a prior reaction to IV contrast. The old IV contrast given many years ago for IVP studies was more allergenic than what is currently used today. A patient history of shellfish allergy is no longer considered a significant risk for an adverse contrast reaction, although it is known that patients who have food/environmental allergies or atopy do have a slightly higher risk of a reaction than patients with no such history. The typical outpatient premedication is:
Prednisone, 50mg by mouth, three doses taken 13 hrs, 7 hrs, and 1 hr before IV contrast is given. 50 mg of Diphyenhydramine (Benadryl®) is also given 1 hr prior to contrast as well (by mouth usually but can be given IV)
In the emergent setting where contrast must be given without the above preparation strategy, IV steroids are used although this is less desirable. Despite IV route these steroids should be given 4 hours prior to the study to have an effect. 50 mg IV diphenhydramine should also be given 1 hr prior to contrast. Examples of IV steroid regimens (given at minimum 4 hours before the IV contrast and given every 4 hours until contrast is given) :
Methylprednisolone (Solu-Medrol®) 40 mg
Hydrocortisone (Solu-Cortef®) 200mg
Dexamethasone (Decadron®) 7.5 mg
Radiation Safety/Radiation Dose
Brighton is committed to reducing radiation exposure whenever possible. We participate in CT radiation dose reduction strategies in partnership with our hospitals and assist clinicians by providing information when a different imaging option could be used that has no radiation exposure, such as MRI or ultrasound. We abide by the “ALARA” principle, or “As Low As Reasonably Achievable” which aims to reduce radiation exposure to the minimum amount while still getting necessary diagnostic information from a scan. The American College of Radiology also has an “Image Gently” campaign aimed at reducing radiation exposure particularly in pediatric patients . A helpful patient information link is: http://www.radiologyinfo.org/
Contrast induced nephrotoxicity (CIN) refers to injury to the kidneys thought to be attributed to the administration of IV contrast. The exact mechanism of injury is not well understood and is difficult to separate from other factors contributing to kidney injury in patients with other medical problems such as preexisting renal disease, dehydration, heart disease, medication side effects, among others. For healthy patients, contrast is given based on a weight based algorithm. For patients at risk for CIN, the situation is addressed on a case-by-case basis. Usually a discussion between the radiologist and technologist in light of the patients renal function (usually based on the GFR or glomerular filtration rate) occurs to decide if the contrast dose must be reduced, or if contrast should not be given. There are times when the importance of receiving contrast outweighs the risks of CIN, and despite poor renal function contrast may be given with subsequent close monitoring of kidney function. Dialysis patients can be given IV contrast provided they receive dialysis within 24 hrs of the dose.
Although different strategies to reduce CIN have been reported, the only clear and undisputed factor that helps reduce CIN is adequate patient hydration. Typically for patients with a GFR > 60 (units are mL/min/1.73m²) there is no adjustment to the dose. For GFR in the 30-60 range, the dose is reduced. For a GFR < 30 contrast is not typically given unless an emergent situation requires IV contrast despite the risk.
For MRI contrast using gadolinium based contrast, there is an entity called Nephrogenic Systemic Fibrosis that rarely occurs when patients with poor renal function have been given this agent. Although this is different from the above CIN with iodinated contrast, the same type of dose reduction strategies are employed.