The use of injectable radiopaque diagnostic agents may be beneficial in the image enhancement of nonneoplastic lesions. Cerebral infarctions of recent onset may be better visualized with contrast enhancement, while some infarctions are obscured if contrast media are used. The use of iodinated contrast media results in contrast enhancement in about 60 percent of cerebral infarctions studied from one to four weeks from the onset of symptoms.
Sites of active infection may also be enhanced following contrast media administration.
Arteriovenous malformations and aneurysms will show contrast enhancement. For these vascular lesions, the enhancement is probably dependent on the iodine content of the circulating blood pool.
Hematomas and intraparenchymal bleeders seldom demonstrate any contrast enhancement. However, in cases of intraparenchymal clot, for which there is no obvious clinical explanation, contrast media administration may be helpful in ruling out the possibility of associated arteriovenous malformation.
Diatrizoate salts are used for radiographic studies throughout the cardiovascular system.
Intravascular radiopaque diagnostic agents of high concentration are not recommended for cerebral or spinal angiography (see CONTRAINDICATIONS—General), and contrast agents with the lowest compatible viscosity and higher concentration of iodine (310 mg/mL to 480 mg/mL of bound iodine) must be used for angiocardiography. Contrast media approaching serum ionic content and osmolality have less potential for deleterious effects on the myocardium (see PRECAUTIONS—General, Drug Interactions).
Addition of chelating agents may contribute to toxicity in coronary angiography, and the sodium content of angiographic agents used in coronary arteriography is of crucial importance.
In addition to the following general CONTRAINDICATIONS, WARNINGS, PRECAUTIONS and ADVERSE REACTIONS, there are additional listings in these categories under the particular procedures.
Do not use HYPAQUE meglumine 60 percent solution for myelography or for examination of dorsal cysts or sinuses which might communicate with the subarachnoid space. Even a small amount in the subarachnoid space may produce convulsions and result in fatality. Epidural injection is also contraindicated.
Urography and large dose vascular procedures are contraindicated in dehydrated azotemic patients. (See also PRECAUTIONS—General.)
Serious adverse reactions have been reported due to the inadvertent intrathecal administration of iodinated contrast media that are not indicated for intrathecal use. These serious adverse reactions include: death, convulsions, cerebral hemorrhage, coma, paralysis, arachnoiditis, acute renal failure, cardiac arrest, seizures, rhabdomyolysis, hyperthermia, and brain edema. Special attention must be given to insure that this drug product is not administered intrathecally.
Ionic iodinated contrast media inhibit blood coagulation, in vitro , more than nonionic contrast media. Nonetheless, it is prudent to avoid prolonged contact of blood with syringes containing ionic contrast media.
Serious, rarely fatal, thromboembolic events causing myocardial infarction and stroke have been reported during angiographic procedures with both ionic and nonionic contrast media. Therefore, meticulous intravascular administration technique is necessary, particularly during angiographic procedures, to minimize thromboembolic events. Numerous factors, including length of procedure, catheter and syringe material, underlying disease state and concomitant medications may contribute to the development of thromboembolic events. For these reasons, meticulous angiographic techniques are recommended including close attention to guidewire and catheter manipulation, use of manifold systems and/or three-way stopcocks, frequent catheter flushing with heparinized saline solutions and minimizing the length of the procedure. The use of plastic syringes in place of glass syringes has been reported to decrease but not eliminate the likelihood of in vitro clotting.
Excretory urography is potentially hazardous in patients with multiple myeloma. In some of those patients, therapeutically resistant anuria resulting in progressive uremia, renal failure and eventually death has followed this procedure. Although neither the contrast agent nor dehydration has been proved separately to be the cause of anuria in myelomatous patients, it has been speculated that the combination of both may be causative. The risk of excretory urography in myelomatous patients is not a contraindication to the procedure; however, they require special precautions. Partial dehydration in the preparation of these patients for the examination is not recommended since this may predispose to the precipitation of myeloma protein in the renal tubules. Myeloma, which occurs most commonly in persons over age 40, should be considered before instituting urographic procedures.
Contrast media may promote sickling in individuals who are homozygous for sickle cell disease when the material is injected intravenously or intra-arterially.
Administration of radiopaque materials to patients known or suspected of having pheochromocytoma should be performed with extreme caution. If, in the opinion of the physician, the possible benefits of such procedures outweigh the considered risks, the procedures may be performed; however, the amount of radiopaque medium injected should be kept to an absolute minimum. The blood pressure should be assessed throughout the procedure and measures for treatment of a hypertensive crisis should be available.
Recent reports of thyroid storm occurring following the intravascular use of iodinated radiopaque diagnostic agents in patients with hyperthyroidism or with an autonomously functioning thyroid nodule suggest that this additional risk be evaluated in such patients before use of HYPAQUE meglumine.
Contrast media administered for cardiac catheterization and angiocardiography may cause cellular injury to circulating lymphocytes. Chromosomal damage in humans includes inhibition of mitosis, increases in the number of micronuclei, and chromosome aberrations. The damages appear to be related to the contrast medium itself rather than to the x-ray radiation. It is to be noted that those agents have not been adequately tested in animal or laboratory systems.
Urography should be performed with caution in patients with severely impaired renal function and patients with combined renal and hepatic disease.
Subcutaneous extravasation, chiefly because of hypertonic cellulitis, causes transitory stinging. If the volume extravasated is small, ill effects are very unlikely. However, if the extravasation is extensive especially in poorly vascularized areas (eg, dorsum of the foot or hand), and especially in the presence of vascular disease, skin slough may occur. Injection of sterile water to dilute or addition of spreading agents to speed absorption have not been successful and may aggravate the condition.
Selective spinal arteriography or arteriography of trunks providing spinal branches can cause mild to severe muscle spasm. However, serious neurologic sequelae, including permanent paralysis, have occasionally been reported. (See also ANGIOGRAPHY, Precaution.)
In patients with subarachnoid hemorrhage, a rare association between contrast administration and clinical deterioration, including convulsions and death, has been reported. Therefore, administration of intravascular iodinated ionic contrast media in these patients should be undertaken with caution.
Diagnostic procedures which involve the use of radiopaque diagnostic agents should be carried out under the direction of personnel with the prerequisite training and with a thorough knowledge of the particular procedure to be performed. Appropriate facilities should be available for coping with any complication of the procedure, as well as for emergency treatment of severe reactions to the contrast agent itself. After parenteral administration of a radiopaque agent, competent personnel and emergency facilities should be available for at least 30 to 60 minutes since severe delayed reactions have occurred (see ADVERSE REACTIONS—General).
The possibility of a reaction, including serious, life-threatening, fatal, anaphylactic or cardiovascular reactions should always be considered (see ADVERSE REACTIONS). It is of utmost importance that a course of action be carefully planned in advance for immediate treatment of serious reactions, and that adequate and appropriate personnel be readily available in case of any reaction.
Preparatory dehydration for angiography and CT procedures is unnecessary and may be dangerous, contributing to acute renal failure in infants, young children, the elderly, patients with preexisting renal insufficiency, patients with advanced vascular disease, and diabetic patients. Dehydration in these patients seems to be enhanced by the osmotic diuretic action of urographic agents. Overnight fluid retention for urography may be undesirable and is considered unnecessary when using this relatively high (60%) concentration.
Although azotemia is not a contraindication, the medium should be used with great care in patients with advanced renal destruction associated with severe uremia. (See also EXCRETORY UROGRAPHY, precautions).
Acute renal failure has been reported in diabetic patients with diabetic nephropathy and in susceptible nondiabetic patients (often elderly with preexisting renal disease) following excretory urography. Therefore, careful consideration of the potential risks should be given before performing this radiographic procedure in these patients. (See also, EXCRETORY UROGRAPHY, precautions—Preparatory Dehydration.)
Immediately following surgery, excretory urography should be used with caution in renal transplant recipients.
The possibility of an idiosyncratic reaction in susceptible patients should always be considered (see ADVERSE REACTIONS—General). The susceptible population includes patients with a history of a previous reaction to a contrast medium, patients with a known sensitivity to iodine per se, and patients with a known clinical hypersensitivity: bronchial asthma, hay fever, and food allergies.
The occurrence of severe idiosyncratic reactions has prompted the use of several pretesting methods. However, pretesting cannot be relied upon to predict severe reactions and may itself be hazardous for the patient. It is suggested that a thorough medical history with emphasis on allergy and hypersensitivity, prior to injection of any contrast media, may be more accurate than pretesting in predicting potential adverse reactions.
A positive history of allergies or hypersensitivity does not arbitrarily contraindicate the use of a contrast agent, where a diagnostic procedure is thought essential, but caution should be exercised (see ADVERSE REACTIONS—General). Premedication with antihistamines or corticosteroids to avoid or minimize possible allergic reactions in such patients should be considered. Recent reports indicate that such pretreatment does not prevent serious life-threatening reactions, but may reduce both their incidence and severity.
Due to the transitory increase in the circulatory osmotic load, injections of urographic agents should be used with caution in patients with congestive heart failure. Such patients should be observed for several hours following the procedure to detect delayed hemodynamic disturbances.
General anesthesia may be indicated in the performance of some procedures in young or uncooperative children and in selected adult patients; however, a higher incidence of adverse reactions has been reported in these patients, and may be attributable to the inability of the patient to identify untoward symptoms, or to the hypotensive effect of anesthesia which can reduce cardiac output and increase the duration of exposure to the contrast agent.
Seizure activity is rare (about 0.01%) on intravenous injection of ionic contrast media. However, in the higher doses used for CT in patients with brain metastases the incidence can be much higher (1% to 10%). In these patients prophylactic use of a small parenteral dose of diazepam is suggested immediately before injection when extra high dose CT regimens are employed.
In addition to the general precautions already described, excretory urography, cholangiography, and other uses also have hazards associated with the particular techniques employed. (See INDIVIDUAL INDICATIONS AND USAGE section.)
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