Radiopaque contrast agents are often used in radiography and fluoroscopy to help delineate borders between tissues with similar radiodensity. Most contrast agents are iodine based.
Iodinated contrast agents may be
Ionic contrast agents, which are salts, are hyperosmolar to blood. These agents should not be used for myelography or in injections that may enter the spinal canal (because neurotoxicity is a risk) or the bronchial tree (because pulmonary edema is a risk).
Nonionic contrast agents are low-osmolar (but still hyperosmolar relative to blood) or iso-osmolar (with the same osmolarity as blood). Newer nonionic contrast agents are now routinely used at nearly all institutions because they have fewer adverse effects.
The most serious contrast reactions are
Contrast nephropathy (renal damage after intravascular injection of a contrast agent)
Allergic-type contrast reactions
Reactions vary in severity:
Mild (eg, cough, itching, nasal congestion)
Moderate (eg, dyspnea, wheezing, slight changes in pulse or blood pressure)
Severe (eg, respiratory distress, arrhythmias such as bradycardia, seizures, shock, cardiopulmonary arrest)
The mechanism is anaphylactoid (see Anaphylaxis Anaphylaxis Anaphylaxis is an acute, potentially life-threatening, IgE-mediated allergic reaction that occurs in previously sensitized people when they are reexposed to the sensitizing antigen. Symptoms... read more ); risk factors include the following:
A previous reaction to injected contrast agents
Treatment begins by stopping contrast infusion.
For mild or moderate reactions, diphenhydramine 25 to 50 mg IV is usually effective.
For severe reactions, treatment depends on the type of reaction and may include oxygen, epinephrine, IV fluids, and possibly atropine (for bradycardia).
In patients at high risk of contrast reactions, imaging tests that do not require iodinated contrast should be used. If contrast is necessary, a nonionic agent should be used, and patients should be premedicated with prednisone (50 mg orally 13 hours, 7 hours, and 1 hour before injection of contrast) and diphenhydramine (50 mg IV, IM, or orally 1 hour before contrast administration). If patients require imaging immediately, they can be given diphenhydramine 50 mg IV, IM, or orally 1 hour before injection of contrast and hydrocortisone 200 mg IV every 4 hours until the study is performed, preferably deferring imaging, if possible, until at least 2 doses of hydrocortisone have been administered (see American College of Radiology Manual on Contrast Media).
In contrast-induced nephropathy Contrast Nephropathy Contrast nephropathy is worsening of renal function after IV administration of radiocontrast and is usually temporary. Diagnosis is based on a progressive rise in serum creatinine 24 to 48 hours... read more , serum creatinine typically begins to increase within 24 hours after administration of IV contrast; it peaks between days 3 and 5 and returns to baseline within 7 to 10 days.
Common risk factors include the following:
Preexisting renal insufficiency (elevated creatinine)
Diabetes mellitus Diabetes Mellitus (DM) Diabetes mellitus is impaired insulin secretion and variable degrees of peripheral insulin resistance leading to hyperglycemia. Early symptoms are related to hyperglycemia and include polydipsia... read more , especially in patients with associated chronic kidney disease Chronic Kidney Disease Chronic kidney disease (CKD) is long-standing, progressive deterioration of renal function. Symptoms develop slowly and in advanced stages include anorexia, nausea, vomiting, stomatitis, dysgeusia... read more
Age > 70
Use of other nephrotoxic drugs
In patients at risk of acute kidney injury Acute Kidney Injury (AKI) Acute kidney injury is a rapid decrease in renal function over days to weeks, causing an accumulation of nitrogenous products in the blood (azotemia) with or without reduction in amount of urine... read more after receiving iodinated intravascular contrast, the following measures should be considered:
A reduced dose of contrast
Use of an iso-osmolar agent
Many hydration regimens exist. One regimen suggests administration of normal saline at 100 mL per hour for a duration of 6 to 12 hours before the contrast administration and continued for 4 to 12 hours following the contrast injection (see American College of Radiology Manual on Contrast Media).
Administration of N-acetylcysteine has been widely studied and has not been shown to be effective in preventing contrast-induced nephropathy (1 Reference Radiopaque contrast agents are often used in radiography and fluoroscopy to help delineate borders between tissues with similar radiodensity. Most contrast agents are iodine based. Iodinated... read more ).
Patients who are taking metformin and develop acute kidney injury Acute Kidney Injury (AKI) Acute kidney injury is a rapid decrease in renal function over days to weeks, causing an accumulation of nitrogenous products in the blood (azotemia) with or without reduction in amount of urine... read more from contrast administration are at risk for lactic acidosis Lactic Acidosis Lactic acidosis is a high anion gap metabolic acidosis due to elevated blood lactate. Lactic acidosis results from overproduction of lactate, decreased metabolism of lactate, or both. (See also... read more . If the patient has chronic kidney disease Chronic Kidney Disease Chronic kidney disease (CKD) is long-standing, progressive deterioration of renal function. Symptoms develop slowly and in advanced stages include anorexia, nausea, vomiting, stomatitis, dysgeusia... read more with an eGFR < 30 mL/min/1.73 m², already has acute kidney injury, or is undergoing arterial catheterization with a risk of emboli to the renal arteries, metformin should be withheld for 48 hours after contrast administration, and only resumed if kidney function is evaluated and deemed satisfactory. Metformin itself does not pose a risk for the development of contrast-induced nephropathy (see American College of Radiology Manual on Contrast Media).
Because many protocols dealing with contrast agents and reactions are specific and continually updated, it is important to discuss such details with the imaging department.
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