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The clinical practice of diagnostic radiology has been made possible by advances by diagnostic equipment and investigative techniques, as in the contrast media that permit visualisation of the details in the internal structure or organs that would not otherwise be demonstrable. Contrast media can be categorized as drug because the can absorb into the systemic circulation and may affect a physiologic response. When an anatomical area is filled or outlined by contrast media. The image appears to be white (positive contrast) but if it is a negative contrast it makes the organ appear darker. Contrast media are solution or either gasses introduced it to the body to provide contrast between an anatomical organ and its surrounding tissues. To increase the visibility of the structure, barium sulfate is used as a substance. The choice of contrast media is always been debate matter but it is always the responsibility of the radiologist to make a rational decision on selection of contrast media. Physical and physiological principle is necessary to have understanding on because it is involved. The contrast of the ideal should be inert to be non-toxic, easily and should be totally excreted from body. Persist for sufficient length of the time and have different absorptive from the power to the tissue of interest. There are also disadvantages and risk of contrast media.
Types of Contrast Media
There are two types of contrast media, which are positive contrast media this is more radiopaque and negative contrast media is radiolucent. These positive contrast media studies are the best way to detect even minor leakage could be detect on the wall of the organ. Positive contrast media give better contrast and mucosal detail than the negative contrast media. In positive contrast media there are also two types of contrast agent which are iodine based and barium based. Barium is normally used for contrast examination of the gastrointestinal tract and it is not metabolized or excreted. Those day barium is used for cystography and bronchography despite superceded by safer iodine based water soluble, can be found in colloidal suspension which is used for GI examinations, paste normally used for esophageal studies especially if looking for mucosal abnormalities, BIPS used to assess GI motility and for detection of GI obstruction, powder or enema kits. Advantages of barium is insoluble, unable to react with body chemically, it also gives good mucosal detail, there is also no asmotic effect therefore radiodensity persists and the cost of barium is low and it is relatively palatable. The disadvantages of barium are aspiration pneumonia if aspirated and if it leaks into body cavities or organs it may persist indefinitely and can cause granulomatous reactions. On the other hand another positive contrast media is iodine based and they are categorized as ionic water soluble, non-ionic water soluble, oily agents and agents excreted in the bile. The uses of ionic water soluble is to take imaging of Cardiovascular system, urinary system, joints, salivary gland, tear ducts, fistulas or sinuses and gastrointestinal tract. The low osmolar ionic water soluble is safer if cardiac or renal function is poor. High osmotic pressure five to seven time's body fluids can cause adverse reaction such as circulatory effects, palpitation and electrocardiogram (ECG) changes, nausea or vomiting, urticaria, anaphylaxis, extravascular irritation and contraindicated if cardiovascular or renal insufficiency. The side effects can be avoided by studying under general anesthesia performed. Advantage of ionic water soluble and intravenous administration is possible and also excreted by kidney therefore could be used for urographic studies. Non-ionic soluble is the latest agents are iso-osmolar with plasma. The advantages of non-ionic water soluble are there is no ionic charge therefore can be used for myelography, therefore lower osmolarity is safer for cardiographic , renal studies or in neonates and it also has fewer side effects. The disadvantage is it cost more. An oily agent is iodinized oils which could not be mixed with water and this agent is used for imaging lymphatic system, sinus tract and salivary glands. Finally, agents excreted in the bile are chylocystopague can be administered intravenously. Contrast agents with more protein binding capacity, example meglumine, ioglycomate are also excreted in the biliary system. This agent used to image gall bladder and bile ducts. These negative contrast media is normally used together with positive contrast media because it has low specific gravity. Oxygen, air, carbon dioxide and nitrous oxide is combined in negative contrast media. The negative contrast media can be used for cystography, gastrography and also in pericardiography. The disadvantages are negative contrast media does not give as much detail as positive or double contrast media. The usage of carbon dioxide is probably safer because it is due to higher solubility in serum and usage of oxygen is a risk of fire. Advantages of negative contrast media are it is available always and it is also lower cost than positive contrast media. The development of the double contrast technique has been stressed the need for the adequate mucosal coating and also how much of the present manufacturing efforts been taken and are devoted to achieving this, an excess of mucus and the one not collected to the due of the fluid in the stomach are greatly inhibit adequate coating of the gastric mucosa and as it is does hypermotility to the stomach.
Before Contrast Media Examination
In the examination of a patient which is with an adverse reaction, a brief history must be obtained by a nurse or the physician and including a summary of the current symptoms by the patient itself, or any health medical conditions, either the nurse or the physician should also be bothered to ask the patient, are they in any medication, after that vital signs such as general issues, respiratory, temperature, blood pressure and pulse should be assessed, and if any patients with adverse reaction should be monitoring closely until the symptoms have stabilized or resolved and assessment of the patient's airway, breathing and circulation (ABCs) must be remaining to the management of moderate or to severe adverse reactions to iodinated contrast media. Let's say if you have health condition such as history definite of health allergy, asthma, maybe you have done previous contrast media or to any drugs and had reaction towards it, you may need to take Prednisolone 40 mg about 12 hours, 2hours before the examination and depends on heart condition, myelodysplastic syndromes or multiple myeloma and severe diabetes, if you are on diabetic medication Glucophage (Metformin) you have to stop for 48 hours before doing an examination which is requiring intravenous injection. If you are very old above 65 years and very young below 6 years should be restricted to take contrast media. If you have none of the following problems conditions, you would need to only fast such as foods and drinks not to be taken for 4 to 6 hours before the examination is being done. Take note that you should take more water so that your body would not be too dehydrating for those with so much of myeloma or myelodysplastic syndromes for them to do Intravenous Urogram (IVU). The nurses or the doctor will explain to you all the procedure and explanation on the examination before, during and after the examination. If you have any suspected or unsure of the allergies or other health problem you really have to consult the doctor before the examination, so that the doctor can explain properly. Safety way preventing contrast media is through pharmaceutical products which is available to the doctor today and for this reason the concept of therapeutic ration is which could be applied to medicines and it cannot be applied to contrast media. There is one critical area examined during its development is the incidence of different adverse reactions. But the rate of the adverse reactions is actually to iodinated contrast media in market is very low, but such adverse reactions do occur with every pharmaceutical product, it also can be divided into two groups which are those who dependent on the dose and also concentration is the reaction clearly from the contrast media and those that that are independent on the dose and also concentration. The dose dependent reaction adverse are mostly due to the physiochemical on the effects of contrast media, as in like osmolality or an electrical charge and it could even include pain, heat , vasodilation, cardiac depression and hypotension reaction. Contrast media is like the other drugs you may be more familiar with, in fact, the new generation contrast media is very safe which contain iodine. Even though, like the other drugs can include commonly those who take Panadol or Paracetamol, there are potential risks of reaction to the contrast media. These are also classified into moderate, mild and severe reaction towards contrast media, but with the non - ionic contrast media reactions is reduced markedly and most of the reactions are really mild, transient and do not require treatment, and the majority normally will occur within the 20 minutes of the injection, but if there are a small proportion of delayed reactions may occur up to two to three days after injection, and if it is mild reaction it will cause to the patient to have nausea or vomiting or even both a person may have, the patient will feel generalized transient warmth throughout the whole body and rashes which may also be transient or else lasting a few days, the patient will be given antihistamine for it, and even sneezing , ''running'' nose will occur.
Furthermore, the physicians who are responsible for the imaging study to the patient that requires iodinated contrast media should be able to recognize and treat the acute reactions adverse. The rooms in which imaging contrast study is being operated to be complete with the appropriate basic and advanced life support monitoring equipments and also drugs, the equipment and the drugs should regularly checked properly.
In the treatment of adverse reactions, immediately discontinue ICM administration. Monitor the patient's cardiac rhythm, blood pressure, and oxygen saturation. Mild reactions are self-limiting and do not require treatment. However, the patient should be closely monitored until the symptoms resolve.
In moderate reaction the patient will have difficulty in breathing, like an asthma patient but there will be treatment given immediately, it happen rarely because this is severe to be a life threatening, but hypotension it may cause sudden drop in the blood pressure and this also immediate treatment given, but normally this transient is not that severe. In the case of severe and life threatening it is very rare with the new and the modern iodine containing contrast media and in this case anaphylactic shock will happen suddenly but it is an unpredictable reaction towards the contrast media reaction.
Finally, the prevention with early identification of patients is at risk at time of the referral for a contrast media - enhanced imaging examination is very crucial. The risks should be balanced against the possible of the benefits. Imaging techniques are alternative that do not require the administration of the iodinated of the contrast media also should be considered and if contrast media is to be given to high risk patients, precaution and carefully, should be taken more with the adequate hydration and also the use of low osmolar contrast media and in attention with the prompt treatment to whenever any adverse events are the keys to strategies.