CT can distinguish tissues or lesions with very similar densities, so the images are clear, there are no overlapping structures, and the tissue density is finely displayed, and has been widely used in various clinical medical fields such as the central nervous system, respiratory system, digestive system, urinary and reproductive system, and bone and joint system.
However, there are some lesions that can only be shown clearly on enhanced scans, and contrast must be used for vascular examinations in various parts of the body. This makes it dangerous to do enhanced CT because – allergy to contrast agent for enhanced CT examination can be fatal!
What contrast agent is used in enhancement scans?
In the first part of the last century, scientists discovered that iodine solution can develop film under X-ray irradiation, which means that iodine solution has the property of absorbing X-rays.
This means that iodine solution has the property of absorbing X-rays. Therefore, medical doctors used the property of iodine to make a special contrast agent for medical radiological examination. The initial contrast agents were ionic contrast agents, in which iodine was present in solution as an ion. The iodine ions, which move freely, come into contact with the blood vessel walls very easily, and when the cells of the human blood vessel walls or other tissues are allergic to iodine, the person using the contrast agent will have an allergic reaction. In order to reduce the occurrence of iodine allergic reactions, medical practitioners, after continuous exploration, found that if the free iodine ions are wrapped with some special chemical structures, just like people wrap very sticky objects with paper to avoid sticking to their hands, ionic iodine becomes non-ionic iodine, so that it is difficult to come into contact with blood vessel walls or tissue cells, and this contrast agent is called non-ionic contrast agent.
What are the adverse effects of contrast media?
During an enhancement scan, a large amount of contrast is injected into the patient’s vein. Generally speaking, contrast agents are safe for humans. However, due to individual differences in the human body, some people may have some adverse reactions to contrast agents under certain circumstances, including allergic reactions and neurotoxicity, vascular toxicity, and nephrotoxicity, among which allergic reactions are the most common. Allergic reactions can be classified as mild, moderate or severe according to their severity.
Mild allergic reactions.
The incidence is 3% to 4%, mainly manifested as skin redness, urticaria, nausea, dizziness, hot and itchy throat, sneezing.
Moderate allergic reaction.
The incidence is 1% to 1.5%, mainly manifesting as generalized hives, slight throat edema, and transient drop in blood pressure.
Severe allergic reactions.
Rarely, the incidence is only 0.01% to 0.05%, mainly manifested as a significant drop in blood pressure, shock, severe tracheal and bronchial edema spasm, severe laryngeal edema, and may even cause death. The rate of adverse reactions of non-ionic contrast agents is significantly lower than that of ionic contrast agents. The incidence of adverse reactions is even lower with modern new non-ionic contrast agents.
In general, all ionic contrast agents require allergy testing prior to use. Non-ionic contrast agents are relatively safe. According to the latest pharmacopoeia issued in China, these contrast agents do not require allergy testing before injection. However, there are some non-ionic contrast agents that still require allergy testing as stated in the instructions for use. For those who have a history of iodine allergy, although it is not an absolute contraindication, great caution is needed when injecting.
Therefore, for the sake of insurance, doctors usually treat them as absolute contraindications. It should also be used with caution in the elderly and young children with high risk factors, in patients with bronchial asthma, cardiac or hepatic or renal insufficiency, hyperthyroidism, or when the patient’s serum creatinine exceeds 3 mg/dl. Generally, patients should be observed for 1 hour after contrast, as there are occasional cases of delayed allergic reactions.
CT examinations should be used with caution!
Due to the possibility of the above-mentioned adverse reactions of contrast agents, patients need to read the informed consent form carefully before receiving CT-enhanced scans and fully understand its contents. Finally, they should sign the informed consent form to indicate that they fully understand the contents and agree to undergo the test.
Some people may ask: Since contrast can cause adverse reactions, wouldn’t it be safer to choose only non-enhanced CT scans? It is up to the physician to weigh the necessity and risk of the test based on the patient’s condition and the patient’s physical condition at the time.
It should be noted that modern medicine is not yet capable of completely avoiding the harm caused by contrast media to the human body. The relevant medical regulations in China require that CT laboratories of medical institutions have a sound system of treatment for side effects of contrast agents.
The CT examination rooms in regular medical departments should be equipped with perfect first aid facilities, and the relevant medical personnel should also have good technical training and rich experience in resuscitation to ensure that patients can receive active and correct treatment in the shortest possible time in case of allergic reactions, so as to ensure the safety of patients’ lives to the maximum extent.