Current Clinical Concerns in CT: Results : IV Contrast Administration
Premedication/Reactions
1. Everyone seems to have a different premedication regimen and I am trying to set up protocols and policy for our first outpatient scanner. We use a regimen that includes Benadryl in the hospital, but I am trying to avoid this because of patients driving to the outpatient center. Would 50 mg of prednisone 24, 12 and 2 hours before the scan be appropriate premedication?
| Answer: We use 40 mg of prednisone at 24, 12 and 2 hours prior to the scan. |
2. What is the steroid prep protocol used at your institution for ER patients? We are currently using Hydrocortisone (200 mg, q 2 hrs) and diphenhydramine (50 mg IM), but there is confusion. Do we scan during the 2 hour window or after the 2 hours have passed? Administer PO, IV or IM?
| Answer: For a 24 hour prep, we use 40 mg prednisone at 24, 12 and 2 hours. If the patient needs an emergent scan, 100 mg of hydrocortisone and then scan is usually the protocol I have seen. Waiting longer will not make too much difference, but 200 mg is a large dose. Where did you get those numbers? |
3. What is the current practice for patients with shell fish allergy requiring iodine contrast? Is there really any proven cross reactivity? Is premedication required? What if it is a severe anaphylactic to shellfish? Are there any recent articles in the radiology literature discussing this issue? Some of our referring physicians do not think premedication should be required.
| Answer: Our experience is that isolated allergies to shellfish do not put you at a higher risk for contrast allergy. We are more concerned with patients who have multiple allergies. |
4. I have recently change the concentration of contrast for all our CTs from Omnipaque 320 to 350. I have also changed the injection rate from 2 cc/sec to 3 cc/second. While we are getting much better images with our Toshiba multislice CT, we are also noticing an increased rate of reaction. I wanted to know if you think this might have something to do with the changes I made.
| Answer: Unlikely-just a coincidence. We use Omnipaque 350 routinely and have no reactions (almost none). There is however, no relationship between concentration and reaction rate. With ionic contrast, we had more reactions at higher injection rates but do not see this occurring with non-ionics. Do you keep your contrast in a warmer? |
5. We have some rads (outpatient practice) in our group who premedicate for any food allergy (seafood, etc,), asthma (including childhood asthma, inhaler for anything), multiple drug allergies (including gadolinium allergy), amongst other things. What do you use as indications for premedication in your practice, and if there is any clear literature on it?
| Answer: We premedicate patients with multiple drug allergies, multiple food allergies or previous allergic reaction to contrast material. |
References
Michael A. Bettmann Frequently Asked Questions: Iodinated Contrast Agents
RadioGraphics 2004; 24: 3-10.
- Summary: Many of the questions presented here are addressed in this recently published Radiographics article, which serves as an excellent reference.
Coakley FV. Panicek DM. Iodine allergy: an oyster without a pearl? AJR 1997; 169(4):951-2.
- Summary: This opinion briefly reviews immunology, the mechanism of idiosyncratic vs. nonidiosyncratic reactions to iodine, hypersensitivity reactions to seafood and cross-reactivity. The authors cite evidence of contrast material sensitivity and seafood allergy and that patients with a history of seafood allergy have a 3 fold risk of adverse reaction to contrast material.