How do radiologists ensure the risk to their patients is minimised and that the number of reactions they observe are the fewest possible? According to Cohan, the first step is to identify patients who are at increased risk of having an acute allergic-like reaction. The three commonly acknowledged risk factors for acute allergic-like reactions include patients who have had a prior adverse contrast reaction of the allergic-like type, patients with allergies to other substances, and patients with a history of asthma.
"Not surprisingly, the patients who are at the highest risk of having an allergic-like reaction are those who have had previous reactions to the same kind of contrast material," he says. "It's not a complete guarantee that someone will have the same reaction, but a subsequent allergic reaction is much more likely, compared with patients who haven't had reactions before. It has been estimated that the increased risk in these prior reactors is about five-fold. Not quite at the same level are patients who have allergies to other substances, including foods and other medications and asthmatics. Prior studies have found that the risk of an acute allergic-like reaction in these two groups is increased by a factor of about two to three."
There is also a problem with the large amount of patients who have allergies to other medications or foods. Such allergies are very common and may be present in up to 50% of people.
Cohan believes that it is important to have a number of overlapping mechanisms in place to detect patients who are at increased risk of having an allergic-like contrast reaction, so that if one component fails the others may succeed in identifying patients as having an increased risk of having a contrast reaction."Obviously, we wouldn't be doing anything very selective in such a large group by identifying them as being at increased risk," says Cohan. "So, many experts have recommended that we consider those patients who have severe allergies or have many allergies as being particularly at risk, although the data to support this behaviour is not very compelling.This is merely an assumption that many of us make."
"The clerk who schedules an imaging test usually asks the patients the relevant questions," he explains. "The patient is then interviewed by a technologist on arrival in the radiology department. In addition the medical records are reviewed."
WHO IS AT RISK?
- Pt. with RF are at 10X increased risk to develope RF.
- If pt. had a previous reaction, but it is not sure that the pateint will have another one.
- Pt. with asthma, drug or food allergy.
- Sea food allergy
- On nephrotoxic deugs (NSAIDS, aminoglycosides)
- Advanced age is risk for RF.
- Metformin (Glucophage), has been associated with the development of severe lactic acidosis following administration of intravenous contrast media.
- Experts recommend stopping metformin therapy at the time of the procedure, or before, and for at least 48 hours following the administration of contrast material.
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