IV Contrast
1. Why do we use IV contrast material? | |
2. Do you use serum creatinine levels or GFR in your practice for establishing risk prior to CT scanning? | |
3. What is GFR and why is it a more accurate measure than simply getting a creatinine level? | |
4. Why are GFR numbers different for Caucasians and African Americans? | |
5. Are all CT scans with IV contrast done the same way? | |
6. What type of IV contrast material do we use and why? | |
7. At what temperature do we store IV contrast material? | |
8. Why do you warm IV contrast? | |
9. What is the advantage of Visipaque as written in the literature? | |
10. When do you use Visipaque-320 and when Omnipaque-350? | |
11. Does the concentration of contrast mean that higher concentrations are better (AKA-isn’t a higher number better)? | |
12. What is the volume of IV contrast material we use? | |
13. What patients are considered high risk patients for IV contrast for CIN? | |
14. Do we have set cutoffs for creatinine levels and if so what are they? | |
15. Can we pretreat patients who have borderline renal function? If yes then how? | |
16. Should patients be NPO for CT scanning? If yes for how long? | |
17. What are the common volumes of contrast used for IV injection? | |
18. What kind of IV access is ideal for use for IV contrast injection? | |
19. Has there been any new developments in technology that may help us high injection rates in patients who can not tolerate an 18g needle (or at times even a 20g)? | |
20. Can any IV the patient has in place be used to inject the contrast material? | |
21. Can we use a central line or a PICC line for injection? | |
22. What about the new “purple PICC/central lines” I hear about? | |
23. What are some of the common normal “side effects” of IV contrast agents? | |
24. Is there a relationship between patients receiving chemotherapy and CIN? | |
25. Is it ok for patients to have both an MR and a CT with contrast on the same day? | |
26. Have you ever seen a patient develop diffuse erythema distal to the IV injection site in the absence of extravasation? | |
27. Patients often report a metallic taste in their mouth following use of IV iodinated contrast. Is there an explanation? | |
28. Are there any contrast volume limitations for the use of IV contrast? | |
29. Can you tell me a bit more about GFR and what it really means? | |
Here is an excellent summary from Richard Vitti MD and Patricia Lewis RT on the subject; It is considered good Radiologic practice to screen patients for renal dysfunction prior to the administration of any iodinated or gadolinium-based contrast medium. The American College of Radiology recommends that all practitioners screen patients for renal dysfunction; this can easily be done by questioning the patient or by chart review, looking for a history of renal disease/transplant, diabetes mellitus, long-standing hypertension, diuretics or nephrotoxic drugs, multiple myeloma, hyperuricemia, or advanced age (≥70 years). If renal dysfunction is present or suspected, then laboratory measurements of renal function should be obtained. The US FDA recommends that patient renal function be assessed either by history or laboratory measurements prior to the administration of gadolinium-based contrast agents. Renal function can be evaluated by obtaining laboratory measurements of blood urea nitrogen (BUN) and serum creatinine (SCr), but neither are sensitive measures of renal function. SCr is influenced by the patient’s gender, muscle mass, nutritional status, and age. GFR is traditionally considered the best overall index of renal function in health and disease. Direct measurement of GFR (or CrCl using the compound inulin) would be the most accurate method of defining renal function, but this requires timed urine collections or radioisotope elimination methods, and thus is difficult to measure in clinical practice. Therefore, most people estimate the GFR from the SCr using specially derived predictive equations. The GFR may be estimated using several formulae, but the most common are:
Cockcroft-Gault equation for estimating GFR (CrCl): eGFR = [(140-age) X body weight (kg) X 0.85 (if female)] ÷ [72 X SCr (mg/dl)] The most widely used method for estimating GFR, this equation considers age, sex, body weight, and SCr in estimating GFR. It is thought to more accurately reflect creatinine clearance. This equation was validated in group of normal volunteers (Canadian Mounties) and is considered by some to be inaccurate as renal function decreases. Schwartz formula for the prediction of GFR in children: GFR(ml/min per 1.73 m2) = 39.1[height (m)/Scr (mg/dl)]0.516 X [1.8/cystatin C (mg/L)]0.294[30/BUN (mg/dl)]0.169[1.099]male[height (m)/1.4]0.188 Cockcroft-Gault also works well in children. Modification of Diet in Renal Disease (MDRD) for deriving CrCl (GFR): eGFR = 186 x SCr-1.154 X (age)-0.203 X (0.742 if female) X (1.210 if black) The MDRD formula is based on GFR values measured by iothalamate clearance in 1628 adults and subsequently validated in another 1775 adults in the African American study of Kidney Disease. The four-variable MDRD Study equation uses age, sex, race, (African-American vs. non-African-American) and SCr. This equation does not require a body weight because it normalizes GFR for a standard body surface area of 1.73 m2. The MDRD formula has been demonstrated to be useful for chronic kidney disease patients and performs similarly in diabetic and non-diabetic individuals, but its use is unclear in healthy individuals and is not recommended for hospitalized patients. The MDRD formula is the recommended method for estimating GFR among Nephrology specialists. These formulae are available at several websites and can be downloaded into hand-held computers for easy access. There are also simple cardboard “slide-rule” style calculators available from GE Healthcare, and while these are “low-tech”, they are convenient to use and require no batteries. RENAL DYSFUNCTION There is no uniform definition of renal dysfunction. When CrCl is less than 60 ml/min (in a normal young adult equivalent to a SCr of 133 mmol/L or 1.5 mg/dl) the term “renal insufficiency” has been used, and when CrCl is less than 30 ml/min the term “renal failure” is often used. Discussion: The most accurate results are obtained with the Cockroft-Gault equation, whereas the most precise formula is the MDRD study equation. The predictive capabilities of these formulae are suboptimal for ideal patient care, but are superior for assessing renal function compared to a simple SCr measurement. Recall that a raised SCr implies that GFR has been reduced by at least 50%, making the patient at risk for developing contrast-induced acute kidney injury (CIAKI). Some investigators have proposed using “cut-off” values for SCr and/or eGFR Cut-off values: eGFR < 80 ml/min, or eGFR < 60 ml/min, or eGFR < 30 ml/min, or The use of cut-off levels, especially the low levels, will include several patients with normal renal function and the use of the high levels will exclude patients with renal impairment.
It is the responsibility of each Radiologist or other prescriber to have a protocol in-place to identify patients for CIAKI. The referring physician must be involved in identifying patients at-risk so the necessary precautions can be taken in time. A recent SCr level should be obtained in patients with a history of risk factors. Professional guidelines have been produced and are helpful for crafting local standard procedures. References:
APPENDIX OF NORMAL VALUES Serum Creatinine (SCr) < 1.5 mg/dl (< 133 µmol/L) Blood Urea Nitrogen (BUN), aka serum urea nitrogen, 10-20 mg/dl (3.6-7.1 mmol/L) Clearances, corrected to 1.72 m2 body surface area Endogenous creatinine clearance: 1.5-2.2 ml/s, or 91-130 ml/min Urea: 1.0-1.7 ml/s, or 60-100 ml/min Prepared by: Richard A. Vitti, MD |