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Contrast media are widely used in imaging, usually with CT, MRI, X-ray and more recently by ultrasound. Iodinated contrast media is the most common contrast agent used and assist in distinguishing between normal and pathological areas. common indication for contrast media, including inflammatory conditions, infectious or neoplastic. However, intravenous contrast is shown when the contrast will increase the diagnostic value. In patients with impaired renal function, non-contrast scans or alternative imaging examination can provide adequate diagnostic information.
Iodinated contrast media
Iodine-based agents iodobenzoic acid compound 2,4,6-tri. Intravascular administration of iodinated contrast media followed by a section that is fast to the extracellular space, the volume of water that moves into the circulation and then mainly through renal excretion. iodinated contrast media classified as non-ionic and ionic.These may have a high osmolality (ionic monomer) or a low osmolality (ionic dimer, non-ionic monomer iopromide for example, and non-ionic dimer). Contents osmolality, viscosity and iodine contrast media are closely related. Side effects increased with higher osmolality. Iodine content is not an independent indicator of adverse events.The non-ionic dimers are preferred because of lower osmolality and less.But chemotoxicity they are more resilient than the non-ionic monomer, and more expensive.
Iopamidol is a non-ionic monomer is used that is two times the plasma osmolality, iodine concentration 300 mg / mL. Iodixanol is a non-ionic dimer, and the iodine concentration of 300 mg / mL was close to plasma osmolality (290 m Osmol / kg).Due to higher costs, which are used selectively to inspection at any osmolality can affect the quality inspection (eg, CT angiography and coronary heart disease lower extremity angiography for severe ischemia).
TYPES OF CONTRAST MEDIA
There are two types of contrast media, negative contrast media (more radiolucent than surrounding tissues) and positive contrast media (more radiopaque). They achieve this difference by absorbing less or more respectively of the incident radiation than do the surrounding tissues.
Negative contrast studies will show the location, size and wall thickness of the organ and will show marked wall thickening and large luminal filling defects such as masses or foreign bodies. They give little information about the mucosal surface, smaller filling defects such as bladder calculi may be overexposed and small tears in the wall may be missed.
Positive contrast studies give little more information than negative contrast studies but are the best way of detecting a small defect in the wall of the organ, as minor contrast leakage is easily seen.
Double contrast studies use a small amount of positive contrast medium to coat the mucosal surface of a hollow organ such as the bladder, followed by distension with air. This gives much better mucosal detail than a positive or negative study alone, and will also more reliably show small filling defects in the puddle of residual positive contrast medium.
NEGATIVE CONTRAST MEDIA
The most commonly used negative contrast agent used in veterinary radiography is room air. It is used mainly in the bladder (pneumocystogram) but can also be used in the gastro-intestinal tract (pneumogastrogram, pneumocolon) and in joints (negative arthrogram).
POSITIVE CONTRAST MEDIA
Barium and iodine preparations are the commonest positive contrast media, appearing radiopaque due to their high atomic numbers (56 and 53 respectively). Barium is presented as barium sulphate and iodine as complex organic molecules.
ionic contrast media contraindicated for intrathecal use. Only iotroxate, which binds reversibly to plasma proteins promote the excretion of bile, is approved for intravenous cholangiography in Australia.
Non-iodinated contrast media
These agents are mostly used in ultrasound (microbubble preparation) and MRI MRI.The agents such as Gadolinium is paramagnetic and shorten the T1 relaxation time.They sometimes used in digital angiography reduction in individuals hypersensitive to iodinated radiographic contrast media. a higher volume of contrast needed for sufficient resolution.
Carbon dioxide is also used for digital angiography when compared with iodinated reduction is contraindicated. However, significant technical limitations. This can not be used for angiography in the diaphragm or when a shunt right-to-left, to prevent the occurrence of ischemic brain of the bubble.
Although contrast media are generally safe, side effects sometimes occur.
Hypersensitivity reactions to contrast media, including E anaphylactic IgE-mediated and non-Ig, with mast cell activation, coagulation, quinine and complementary mechanisms, enzyme inhibition and platelet aggregation. 1
mild reactions to low osmolar contrast media media occurs in less than 3% of patients and consisted of skin rash, nausea, flushing or hypersensitivity urtikaria.reaksi moderate and severe, including bronchospasm and wheezing, angioedema, coronary artery spasm, hypotension, cardiac arrhythmias,hilang.Sebaliknya awareness of heart failure and severe reactions are rare, occur in less than 0.04% non-ionic iodinated contrast injection. Deaths due to contrast media reaction is low (less than one death in 100 000 patients). 2, 3
Inside, parental death associated with contrast media administration was significantly higher. Children are more sensitive to changes in fluid volume associated with contrast administration.
Even small doses can cause the injection of iodinated contrast reaction.Test no reaction recommended.The reaction may occur immediately, but was postponed after an hour or sometimes a week can also occur.These reaction (2-5%), but not for their possible anaphylaxis T cell-mediated and may consist of urticaria, rash angioedema.The makulopapular and related osmolality contrast media reaction.Contrast media that is most serious non-fatal reactions can be prevented by using lowosmolar contrast media.
Previous reaction to contrast media is the most important risk factors and bring the absolute risk of 20-60% when exposed to the next. Asthma increases the risk significantly, especially the risk of bronchospasm. Beta blockers have been associated with hypersensitivity and may worsen bronchospasm. A history of allergies require several treatments to increase the risk of acute reaction to iodinated contrast three to five times. Vasovagal reactions may occur during intravenous contrast media.
If reactions occur, intravenous contrast media must be stopped immediately.Despite mild reactions are often self-limiting and resolve without specific treatment, a reaction that began during or shortly after injection must always be regarded as symptoms progress. Vasovagal reactions are treated with lower body height, and 0.6 mg of atropine as light indicated.Treat delayed hypersensitivity reactions with oral antihistamines.
Reactions associated with bronchospasm and wheezing, stridor or laryngospasm and hypotension should be treated with adrenaline, intravenous fluids and oxygen, other antihistamines with or without hydrocortisone. Intubation may be needed and medications may be needed to support the case for 2-3 days berat.adrenalin Intramuscular (1:1000) is the mainstay of treatment for severe reactions and can be repeated every 5 minutes if necessary. The initial dose for adults is 0.25-0.5 mL for those weighing less than 50 kg and 0.5 mL for those weighing more than 50 kg.Corticosteroids not useful in the early management of E-mediated reaction of non-Ig, but is believed to prevent or reduce the symptoms is delayed. Most patients recover from their reaction with no long-term morbidity. 4 Patients who experience severe reactions should be encouraged to carry Medic Alert card. severe reactions should be reported to the Office of Drug Safety (www.tga.gov.au / ADR / bluecard.htm).
Patients with recurrent reaction to contrast media can not be given so that other modalities should be considered for investigation. However, when intravascular iodinated contrast must be given, a different agent and should be used for low osmolar and premedication with corticosteroids for 24-48 hours before the procedure is widely practiced.
In this case, arterial vasoconstriction and renal tubular changes in glomerular hemodynamics because of the quality of plasma oncotic pressure caused by renal insufficiency kontras.Pada media, acetylcysteine (a vasodilator and antioxidant) and fenoldopam (a vasodilator) has been studied as a prevention strategy with no positive outcome uncertain. 5
Acute kidney injury in patients who can not be hydrated and have normal renal function receiving contrast media is less than 4 mL / kg. In patients with mild renal impairment, hydration before contrast media injection usually prevent kidney function decline.
research alternatives such as non-contrast MRI, ultrasound and digital angiography reduction of carbon dioxide should be considered in patients with moderate to severe renal impairment. dimeric non-ionic contrast media have the advantage of not more than monomer contrast media in relation to contrast-induced nephropathy. 6
Most hospital based radiology practice now requires the measurement of serum creatinine and calculated glomerular filtration rate (GFR) before injection of contrast media.This because kidney failure is a potential factor in the hospital and the death of long-term mortality of older patients with mild renal impairment. 7 If a GFR less than 60 mL/min/1.72m 2, urged caution and patients should be sufficiently hydrated when iodinated contrast medium Gadolinium or used.
Metformin has been associated with some cases of kidney failure and lactic acidosis in patients receiving contrast media. If contrast media cause renal failure, metformin, a renally produced, can reach toxic levels cause lactic acidosis. Now it is suggested that metformin be stopped at least 12 hours before the contrast study and will not be extended for at least 36 hours after the procedure, and longer if the serum creatinine had not returned to the beginning. Alternative Method of patient glucose management may be needed during that time period.
The most important factor in reducing contrast-induced nephropathy are:
Avoid repeating the study on high dose short interval
adequate hydration with intravenous access if necessary
Low use of non-ionic contrast medium osmolar
the use of diluted contrast medium at the lowest practical volume
avoid using the same drugs that can cause renal vasoconstriction (anti-inflammatory non-steroid).
In most cases, renal function returned to the beginning without special treatment.In severe cases treatment is the same as for patients with tubular necrosis from other causes.
Nephrogenic systemic fibrosis
Gadolinium-based agent associated with nephrogenic systemic fibrosis in patients with depressed renal function. 8, 9 The majority of cases in people who received high doses for CT or angiography digital Gadolinium reduction in iodinated contrast is known as hypersensitivity.
Patients with a GFR less than 30 ml / min are considered at high risk of nephrogenic systemic fibrosis and the risk of Gadolinium completely.The should be avoided in patients with GFR over 60 ml min / receive low-dose Gadolinium (0.1 ml / kg) is ignored requirements. Research for Gadolinium in patients with mild renal impairment should be determined by clinical reasons.
Iodinated contrast media and thyroid
iodinated contrast-induced thyrotoxicosis is rare. Iodine has no significant effect in patients with normal thyroid function. Patients with multinodular goiter Graves' and the increased risk, and those with thyrotoxicosis should not receive contrast.
Patients with hyperthyroidism may develop thyroid crisis, thyroid function tests and accuracy will be influenced by media.These contrast intravascular contrast media can also affect thyroid diagnostic studies of isotopes up to eight minggu.Pesakit with thyroid carcinoma scheduled for treatment with radioactive iodine should not receive contrast, because can delay the treatment for eight weeks.
Contrast media extravasation
New CT angiographic techniques involving contrast media power injectors, larger volume and higher levels of injection. Consequently there are slightly higher incidence of contrast medium extravasation at or near the injection site. In severe cases, there is a risk of skin loss, although this is less with a low osmolar agents.
Treatment aims to reduce the metabolic needs of the skin with cold compresses for 20 minutes, and increase the absorption of high contrast medium and crepe bandage.
Iodinated contrast media are generally used for imaging with a variety of diagnostic low-osmolar modalities.The, agents of non-ionic monomer contrast with a very low risk of serious reactions. Patients should be carefully evaluated for risk factors, including history of previous reactions to contrast media, asthma, medical conditions with particular emphasis on renal function and thyroid medications, and this time, especially metformin, and beta blockers. severe hypersensitivity reactions should be treated as another anaphylactic reaction with Intramuscular adrenaline.