MDCT Technology – Introduction Technical Considerations Preparing Patients for CE Exams CM Safety
Patients at risk for contrast-induced nephropathy
Temporal resolution is the capability of an imaging system to accurately image and display moving anatomy.
Definition and Risk Factors
In the absence of other causes, contrast-induced nephropathy (CIN) is an acute decline in renal function after the administration of iodinated contrast media. The most common risk factors for developing CIN are shown in Table 1.
|Table 1. Risk Factors for Developing CIN|
Establishing the Current Renal Status of the At-Risk Patient
- Measure serum creatinine within 7 days of the contrast-enhanced examination in non-emergency situations for the following conditions:
- Intra-arterial administration
- Age >70 years
- Diabetes mellitus
- History of renal disease or recent renal surgery
- Recent major surgery or coronary artery bypass graft surgery
- Recent (within 7 days) exposure to radiographic contrast agents
- Concurrent administration of drugs that are directly nephrotoxic or produce intra-renal vasoconstriction
- History of previous episode of CIN
- Obtain the patient’s age, weight, and gender
- Calculate the creatinine clearance using an established formula
Prophylactic Measures for Prevention of CIN
- Consider alternative imaging modalities that do not require the administration of iodinated contrast media.
- Stop the administration of nephrotoxic drugs for 24 hours before and after the contrast-enhanced exam.
- Stop the administration of diuretics (especially loop diuretics).
- Hydrate all patients
- Patients should be properly hydrated before and after contrast administration, especially the at-risk patients.
- Hydration alone is better than hydration combined with a diuretic.
- Intravenous (IV) hydration is reportedly more effective than unrestricted oral fluids.
- Isotonic (0.9% sodium chloride, NaCl) IV hydration is reportedly more effective than half-isotonic (0.45% NaCl) IV hydration.
- The maximum benefit of isotonic IV hydration is seen in women, diabetics, and patients receiving >250 mL contrast.
- IV hydration with 0.9% sodium bicarbonate (NaHCO3) is reportedly more effective than IV hydration with 0.9% NaCl. (Solution: D5 NaHCO3 154 mEq/L; load: 3 mL/kg over 1 hour, given 1 hr before contrast; maintenance: 1 mL/kg/hr for 6 hours after procedure; use 110 kg maximum weight for calculations.)
- Limit the dose of contrast to the minimum needed to obtain images of adequate diagnostic quality.
- Do not perform multiple imaging studies with iodinated contrast agents in a short period of time unless absolutely necessary; try to keep an interval =48 hours between contrast exams.
- Use low-osmolar contrast media
- Nonionic contrast media are less nephrotoxic than ionic, high-osmolar contrast media.
- Even so, nonionic iodinated contrast agents may further deteriorate the renal function of renally-compromised patients.
- Data in the literature do not fully support the efficacy of any pharmacologic premedication with the exception of hydration, as described above.
- Fenoldopam has been proven ineffective at preventing CIN.
- Oral or IV N-acetylcysteine is often recommended, as it is inexpensive and has low risk, but its clinical benefit still needs to be proven. It is also important to note that dialysis rates are not reduced by the use of N-acetylcysteine.
- Theophylline may be of benefit, but needs more study.
Patients at risk for contrast-induced nephropathy
Follow-up of At-Risk Patients
Patients at risk for developing renal impairment should be monitored closely after contrast-enhanced CT examination.
- Discontinue metformin or other biguanide until 48 hours following the procedure; at which time, creatinine should be redrawn. Restart only if and when serum creatinine levels return to normal, or you are certain that the patient is stable.
- Closely monitor urine output, and increase intravenous fluid rate as necessary; input should be greater than output with the goal of maintaining a positive fluid balance and high urine flow rate.
- Consult a nephrologist if patient shows signs of decreased urine output or steady increase in serum creatinine levels.
- Monitor blood urea nitrogen and creatinine levels 24 hours after the procedure. In the case of an increase, the patient should be hospitalized for continued hydration and observation. Serum creatinine levels should be rechecked daily until levels return to baseline.
Features of CIN
The clinical features of CIN are shown in Table 2. Dialysis as a result of CIN is required in <0.3% of patients, but the prognosis is poor, with a higher risk of death, both in-hospital and long-term, especially in patients with pre-existing renal failure.
|Table 2. Clinical Features of CIN|
Patients with immediate-type hypersensitivity to contrast
Identification of Patients at Higher Than Usual Risk
- Patients with a history of allergic reaction to contrast media
- Patients with known risk factors for allergic reactions
- History of multiple allergies (atopia)
- Bronchial asthma
Note : If necessary, select an alternative mode of testing (MRI or US)
Preparation of Hypersensitive Patients
- Always use nonionic low-osmolar contrast media
- Premedicate patients with known allergies to contrast or known risk factors for reactions
- Glucocorticoids ([methyl]prednisolone, hydrocortisone, dexamethasone) 12 to 2 hours before the examination; oral or IV
- H2-antihistamine (cimetidine or ranitidine in saline) 2 hours before the examination; IV: slow injection or infusion.
- H1-antihistamine (diphenhydramine or clemastine) just prior to examination or during examination; IV
Immediate Hypersensitivity Reactions
- Usually occur within 60 minutes postinjection
- Mild to moderate reactions include
- Nausea or vomiting
- Diffuse erythema, angioedema
- More severe reactions that require treatment include
- Laryngeal or pulmonary edema
- Anaphylactic shock
- Respiratory arrest
- Cardiac arrest
Other reactions to IV contrast administration
- Most common complication from IV contrast administration
- Produces an acute local inflammatory response that peaks in 24 to 48 hours
- Patients at risk are those who: are non-communicative and/or severely debilitated; have abnormal circulation in the limb to be injected; and have multiple vein punctures.
- For patients at risk, certain injection sites may be more susceptible and should be avoided, such as the hand, wrist, foot, and ankle.
- Usual symptoms
- Flushing/heat sensation
Note : There are no reported data to support the claim that nonionic contrast media have a significant effect on patient heart rate during intravascular injection. Two studies were conducted in patients who underwent cardiac angiography (N = 120) or peripheral intraarterial digital subtraction angiography (N = 96) in which heart rate was systematically measured before, during, and after injection. In both studies, patients randomly received either a nonionic, low-osmolar monomer or a nonionic, iso-osmolar dimer. There were no significant trends noted in the mean change from baseline in heart rate data for either treatment group in either study.
(Data on file, Bracco Diagnostics” to the 2005 NASCI meeting abstract reference – Meier B, Garachemani A, Fleisch M. Effects of non-ionic iodinated contrast media on patient heart rate during intracardiac or intraarterial injection. Presented at the North American Society of Cardiac Imaging, Amelia Island, Florida, 2005)
Hyperthyroid Episode (“Thyroid Storm”)
- Iodine in contrast agents can stimulate an acute overproduction of thyroid hormone in patients with an occult or overt hyperthyroid condition
- Hyperthyroid conditions include
- Grave’s disease
- Hyperactive nodule
- Toxic multinodular goiter (Plummer’s disease)
- Premedicate hyperthyroid patients
- Sodium perchlorate, 1 day before CT and continued for 8 to 14 days. In emergency CT studies start directly before CT
- Thiamazole, 1 day before CT and continued for 28 days. In emergency CT studies start directly before CT
Delayed Adverse Events
Delayed adverse events (DAEs) can be defined as adverse events occurring 1 hour to as much as 7 days after the administration of iodinated contrast.
- Typical DAEs include
- Skin reactions such as painful itching, skin eruptions, and other maculopapular rashes. These reactions are clearly related to contrast agent administration.
- Other adverse reactions reported include headache, dizziness, nausea, vomiting, diarrhea, chills, and flu-like symptoms. However, the incidence of these delayed reactions in patients who receive contrast media is similar to that reported in patients who receive only noncontrast CT (12.4% vs 10.3%, respectively). 1
- Nonionic dimers such as iodixanol, are associated with a more frequent occurrence of DAEs than nonionic monomers. 2,3
1. Yasuda R, Munechika H. Delayed adverse reactions to nonionic monomeric contrast-enhanced media. Invest Radiol. 1998;33:1-5.
2. Sutton AG, Finn P, Campbell DJ, et al. Early and late reactions following the use of iopamidol 340, iomeprol 350 and iodixanol 320 in cardiac catheterization. J Invasive Cardiol. 2003;15:133-138.
3. Sutton AG, Finn P, Grech ED, et al. Early and late reactions after the use of iopamidol 340, ioxaglate 320, and iodixanol 320 in cardiac catheterization. Am Heart J. 2001;141:677-83.
Treatment of reactions to IV contrast
- Initial treatment includes
- Elevation of the affected extremity above the heart
- Application of cold packs
- Consultation with referring physician
- Most patients recover without sequelae
- Plastic surgery consultation may be required to prevent or treat ulceration or tissue necrosis.
Treating Immediate-Type Reactions
- Oxygen at high dosage via face mask for respiratory, cardiovascular, and neurological reactions
- Antiemetic for nausea and vomiting (though these reactions are usually brief and self-limited)
- Antihistamines, such as ranitidine or diphenhydramine, for symptomatic urticaria, angioedema, or diffuse erythema
- Epinephrine for laryngeal edema, bronchospasm, and generalized or severe angioedema
- Corticosteroids are not useful for treating acute reactions; these may play a role in preventing delayed recurrences up to 48 hours.
- Although rare, cardiovascular and severe respiratory reactions may require emergency treatment and should be handled immediately according to hospital protocol.
Treating Delayed Adverse Events
- At the time of a DAE most patients will be in the care of their primary physician
- Antihistamines may reduce the symptoms of skin reactions but will not eliminate the reactions themselves
Considerations when using gastrointestinal (GI) contrast
Types of GI Contrast
- Negative (hypoattenuating) contrast agents
- Noncarbonated water or juice for specific evaluation of the stomach and pancreas
- Methylcellulose preparations for CT enteroclysis of the small bowel
- Air only for virtual endoscopy of the colon and stomach
- Positive (hyperattenuating) contrast agents
- Barium sulfate suspension for universal applications relating to stomach and bowel (contraindicated if suspected bowel perforation)
- Iodinated solutions for universal applications relating to the stomach and bowel (contraindicated in patients with hyperthyroidism).
When and How to Use GI Contrast Agents with MDCT
- Delineation of the abdominal vessels is assisted by a negative GI contrast agent.
- For the upper abdomen, 500 mL to 1000 mL of negative contrast should be given in a short period of time.
- For the whole abdomen:
- 1 L to 1.5 L of negative contrast can be given 30 to 60 minutes prior to examination, or
- 500 mL to 1000 mL of positive contrast can be given over a period of 30 to 90 minutes prior to the exam, to opacify the distal small bowel and colon, with equal amounts of negative contrast given 15 minutes prior to the exam to assist upper abdominal visualization. Allow time in between to avoid mixing of contrasts.
- For pelvic CT, or for colon and distal small bowel opacification only, can administer positive contrast either orally as described above, or rectally, if necessary.
Multidetector CT Protocols
Developed for GE, Philips, Siemens,Toshiba Scanners
Springer 2005, 2006