Chronic kidney failure no barrier to CT angiography.


CT angiography (CTA) using moderate doses of IV contrast in patients with advanced renal failure is a safe procedure that negatively affects renal function in only a small percentage of patients, according to researchers from Baltimore.

But the imaging options are even better with newer MDCT scanners. CTA protocols with low kVp and using half the normal dose of iodinated contrast have even less impact on kidney patients and produce excellent images, said Dr. Barry Daly from the University of Maryland.

In a study presented at last month’s International Society for Computed Tomography (ISCT) meeting in San Francisco, Daly showed how even normal contrast doses had little effect on serum creatinine levels in most patients. Information gained by the studies far outweighs the chance of adverse effects in patients with chronic renal failure, he said.

Daly also showed his latest protocol for low-contrast-dose, low-kV CTA imaging that delivers high image quality with even less risk for these patients.

Don’t skip the CTA

CTA isn’t something you want to skip, even though many centers do just that, he said. Before renal transplant surgery, for example, surgeons need to see what they’re going to be dealing with in the operating room.

“There are big risks going into surgery without CTA in this group because they have the risk of a major change in operative procedure, prolonged surgery, poor graft outcomes, failure to engraft, loss of the organ — which is a total disaster, especially in the setting of matched renal donor transplantation — and, of course, the possibility of missing important pathologies,” Daly said.

Incidental right iliac venous stent
Patient is in renal failure but not yet on dialysis. CTA was acquired at 80 kVp and 360 mAs following administration of 50 mL of 350 mg/mL contrast. Contrast density in the iliac arteries is > 400 HU. Radiation dose is 4.3 mSv. There is an incidental right iliac venous stent. Images courtesy of Dr. Barry Daly.

Daly and colleagues reviewed the use of CTA in 180 potential renal transplant recipients, all with matched donors, “but we were especially interested in looking at a predialysis cohort of 40 patients,” he said.

Patients were assessed for aortoiliac and calcific atherosclerosis, venous thrombosis, and increased incidence of renal cell carcinoma (four to seven times the normal rate in native kidneys). The only prophylaxis was aggressive oral hydration both before and after CTA, he said.

It’s important to find an appropriate place for the engraftment, Daly said. Many patients may require surgical correction with bypass grafts before transplantation can be done.

“Because a lot of these folks have had chronic hemodialysis, it’s not uncommon to find occlusion of the iliac veins,” he said. In a couple of cases, this has become obvious only in the operating room — “with disastrous consequences.”

The study measured serum creatinine (SeCr) and estimated glomerular filtration rate (eGFR) before and after imaging in the 40 predialysis patients. “There was almost no difference between the two groups in mean measurements,” Daly said.

“Nobody had to undergo dialysis, but looking at the changes, there clearly were some shifts that we shouldn’t ignore,” he said.

Post CTA, 27 patients had stable or mean decreased SeCr of 10.2%. Thirteen patients had a mean increase of 6.3%, with one patient showing a 32% rise, and three saw almost no change (0.5-1.5 mg/dL increase).

Change in SeCr after CTA in predialysis cohort of 40 patients

SeCr mean SeCr range eGFR mean
Pre-CTA 5.2 2.9-14.1 20.5
Post-CTA 5.1 2.4-14.2 21.0

A low rate of contrast-induced nephropathy (CIN) in renal patients isn’t all that surprising, Daly said. Newhouse, Katzberg, and others have shown that the risks of IV low-osmolar contrast precipitating CIN have been overestimated.

These previous studies demonstrate that moderate doses of IV contrast are much less nephrotoxic than arterial administration, he said. Many studies without controls failed to allow for other factors affecting renal function, especially in hospital populations. Finally, a 2010 study in Radiologyshowed that low-osmolar contrast may be as safe as iso-osmolar contrast, he noted.

Low-kVp, low-contrast-dose CTA

Daly and colleagues also performed a study of low-kVp, low-contrast-dose CTA in chronic renal failure patients. Why is this necessary if the regular dose is safe?

“The answer, of course, is that lower is always better,” Daly said. Even if the negative effects aren’t as bad as they were feared to be, “there is still a small portion of patients in our group who are still at risk with the conventional dose,” he said, adding that “new CT scanners have enabled new techniques for getting more out of each gram of iodine.”

The technique involves dropping the kV and increasing the mAs. For example, if you drop the tube current from 120 kV to 80 kV, you would increase the mAs by a factor of 2.7. Thus, 120 kVp and 250 mAs become 80 kV and 600 mAs, he said, and for large patients the tube may reach the maximum mAs.

MDCT can be used with extended z-axis coverage to shorten scan times to correspond to a shorter bolus train. Ideally, there should be at least 40 mm to 80 mm of coverage, he advised.

How it works is by now well-known, he said. “The k-edge of iodine is only [33.2] keV, so by dropping our kVp we can actually get considerably increased x-ray absorption. There’s a nearly a twofold increase in iodine attenuation at 80 kV compared to 120 kV.” Thus, the iodine dose can be cut in half while producing similar CT values, according to Daly.

The researchers perform the 80-kV studies on a Brilliance iCT 256 or a Brilliance 64 scanner (Philips Healthcare) using 320 to 350 mgI/mL of contrast.

They inject 35 to 50 mL of contrast at 4 mL per second in a peripheral vein, followed by 40 to 60 mL of a saline chaser at 4 mL per second. Automated bolus tracking is set for a 120- to 150-HU threshold in the aorta just below the hiatus, and the automated minimum scan delay is set to 4.2 to 6.5 seconds, he said.

Tube rotation speed is 0.75 seconds for a 256-slice scanner and 0.75 to 1 second for a 64-detector-row scanner. mAs values are based on patient body mass index (noise present at precontrast phase) with pitch set at maximum for the mAs selected, Daly said.

The resulting images look great, but using iterative reconstruction (iDose5, Philips) allows even lower doses, or the scanning of larger patients using low-kV, low-contrast protocols, he said.

In summary, CTA with a moderate 100-mL dose of iso-osmolar contrast in advanced renal failure “is a safe procedure with a negative impact on renal function in only a small percentage of patients,” Daly said, adding that “these aren’t patients with creatinine of 1.8, these are patients with major renal compromise.”

However, even though the 100-mL contrast protocol has a “very limited negative effect on people … a better option today is low 80-kVp, low-contrast-dose CTA technique with 35 to 50 mL of iso-osmolar contrast,” Daly said.

This very safe technique yields high diagnostic quality and works on most newer CT scanners, he added.

“Finally, if you have the benefit of iterative reconstruction, it improves image quality and allows us to use this technique even in very large patients,” Daly said.

Higher creatinine can occur after CT — even without contrast.


Contrast media is often blamed for what appears to be contrast-induced nephropathy (CIN) in patients getting CT scans. But Chinese researchers have found that elevated rates of serum creatinine — a marker for CIN — can occur after CT even in

There are lots of reasons why patients could have higher serum creatinine levels after CT exams, according to two studies presented by researchers from Peking University First Hospital in Beijing at the 2013 International Symposium on Multidetector-Row CT. Clarifying those reasons is critical, according to the group.

“There are many factors affecting creatinine levels, especially among inpatients,” said Dr. Xiaoying Wang in her presentation. “Many patients have severe diseases where, due to the disease, doctors find it is not appropriate for them to have contrast-enhanced CT.”

Nailing down renal impairment

The findings don’t necessarily fit with conventional wisdom on contrast-induced nephropathy; however, they do highlight the multifactorial nature of impaired renal function and remind clinicians that several factors must be present for a CIN diagnosis, Wang said.

“The definition of CIN is clear and simple, but in practice it’s not easy to define,” she said. CIN requires an absolute or relative increase in serum creatinine (SCr) compared to baseline values, a temporal relationship between the rise in SCr and exposure to a contrast agent, and the exclusion of alternative explanations for renal impairment — which means looking for these explanations.

“Generally, as radiologists it is easy for us to detect an increase in serum creatinine, but it is not very easy for us — sometimes not even easy for nephrologists — to exclude alternative reasons for renal impairment,” Wang said.

In an effort to identify at-risk patients, in Wang’s practice, patients making appointments for contrast-enhanced CT are asked about a range of factors suggestive of CIN risk. The literature shows higher levels of risk for patients with a history of diabetes mellitus, hypertension, renal impairment, liver disease, renal-toxic medications, and a few other circumstances, though the studies used to identify the risk factors involved intra-arterial injection of contrast agents, Wang said.

Study 1: Are at-risk patients really more at risk for CIN?

For patients undergoing contrast-enhanced CT between 2010 and 2012, her group analyzed the association between risk factors and the subsequent development of CIN. The researchers examined a total of 2,556 patients, of whom 1,243 formed an observation group. The patients were measured for SCr before contrast-enhanced CT as well as 48 to 72 hours after CT; if SCr levels rose by the second test, the patient was referred to a nephrologist, and SCr was measured again seven to 10 days later.

In all, 68 (5.5%) of the 1,243 patients were diagnosed with CIN, including 12 with acute renal failure. (Fifty-one patients recovered and five were lost to follow-up.) However, the study showed no statistically significant difference in the development of CIN between the patients with risk factors and those without.

Of the patients who were not at risk, 4.5% (17/375) developed CIN, while in the at-risk group, 5.9% (51/868) developed the condition (p = 0.21). Among patients with no history of chronic kidney disease, only female gender (p = 0.03) and the use of low-osmolar contrast media (p = 0.03) were associated with a significantly increased risk of CIN.

Logistic regression analysis of risk factors showed several that increased the odds of CIN, including a history of diabetes mellitus (odds ratio [OR] = 1.83), history of tumor (OR = 1.54), use of nephrotoxic drugs (OR = 1.69), frequent use of contrast media (OR = 1.13), and use of low-osmolarity contrast media (OR = 2.28). In addition, women had an odds ratio of 1.69, and those older than 75 had an odds ratio of 1.26. The difference was only statistically significant in women (p = 0.04), however.

“These [risk] factors are not very strong to [predict] the incidence of CIN,” Wang said.

Study 2: Is ‘CIN’ risk really higher after noncontrast CT?

To continue to refine risk-factor prediction, the group recently completed a prospective cohort study of 623 patients who underwent CT with and without contrast. Of the 623 patients, 171 formed an observation group that received multiple SCr tests to allow the nephrologist to confirm a temporal association between increased SCr and contrast administration.

Among these 171 patients, 99 underwent contrast-enhanced CT and 72 had CT without contrast. There was no statistically significant difference in demographics and CIN-related risk factors between the 171 patients and the remaining 452, Wang said.

In all, 17 (9.9%) of the 171 patients developed what appeared to be CIN. Dividing up the patients between those who received contrast and those who did not, seven (7.1%) of the 99 who got contrast developed CIN. Meanwhile, 10 (13.9%) of the 72 patients who did not receive contrast developed “CIN.” Again, the difference in CIN rates between those who did and did not receive contrast was not statistically significant (p = 1.414).

Many factors affect creatinine levels, especially among those like the inpatients in this study, who have a wide range of medical conditions and are prescribed a variety of medications, Wang concluded. Even factors ranging from higher muscle mass to recent ingestion of cooked meat can result in higher SCr levels.

“That’s how we explain the higher SCr levels among noncontrast CT patients,” she said. “The increase of serum creatinine level after CT examination may occur without iodine contrast administration.”

She cautioned, though, that the sample sizes were small in both studies.

Excluding alternative explanations for renal impairment is crucial for diagnosing CIN, Wang concluded, and large, prospective cohort studies are needed to determine the true incidence of CIN in contrast-enhanced CT.

Source: auntminnie.com

Prevention of acute renal failure post-contrast imaging in cardiology: a randomized study..


Abstract

BACKGROUND:

The contrast-induced nephropathy (CIN) is the third most common cause of acute renal failure (ARF) and the worsening in a pre-existing chronic renal failure (CRF), with a foreseeable increase of morbidity, mortality, length of the stay in hospital and, as a consequence, of the health costs. We studied the effectiveness of N-acetylcysteine (NAC) associated with sodium bicarbonate (Na2HCO3) infusion in order to prevent CIN in patients undergoing coronary angiography with administration of contrast medium.

MATERIALS AND METHODS:

296 patients with indication to perform coronary angiography were included in a randomized, observational study. All patients were randomly assigned to receive pre- and post-contrast hydration with 1500 ml of 0.9% saline solution infusion (Group A) or NAC (1200 mg × 2 days) + Na2HCO3 (Group B). The primary end-point was to examine CIN appearance, defined as a raise in serum values of Cr (Creatinine) ≥ 0.5 mg/dl or ≥ 25% within 24-72 hours after the exposure to the contrast medium.

RESULTS:

It has been observed a frequency of CIN of 9.4% in Gr. A compared to 7.2% in Gr. B. Nevertheless, when we put these results through a more accurate screening according to gender, degree of raise in creatinine levels and the extent of change in GFR (glomerular filtration rate), we observed a very different behaviour. In patients with normal Cr and CrCl (Clearance of Creatinine) the frequency of CIN was similar in both group A and B (approximately 5%). In patients with normal Cr but reduced ClCr the use of NAC was more effective than hydration in preventing CIN (0% vs 18% in prevalence respectively in B and A group). In patients with moderately reduced Cr and CrCl, hydration with saline solution was more effective than NAC + Na2HCO3 (8.6% vs 17.6%) while in patients with severe CRF the combined use of NAC + Na2HCO3 showed off to be very successful in preventing CIN compared to the merely hydration (0% vs 50%).

CONCLUSIONS:

In patients affected by severe CRF who are undergoing investigations with contrast medium administration, such as coronary angiography, the combined use of NAC + Na2HCO3 infusion significantly reduces the risk of developing CIN. In other circumstances the final result is related to the degree of previous GFR or creatinine values alteration or to gender. In such situations the combined use of both substances is more questionable and sometimes ineffective.

Source: Pubmed

 

Fibrates and estimated glomerular filtration rate: observations from an outpatient clinic setting and clinical implications.


Previous studies have demonstrated that fibrates have an effect on creatinine concentrations. The pattern of change with fibrates in estimated glomerular filtration rate (eGFR), widely used in clinical practice, has not been previously described.

Methods Data was retrospectively collected from 132 consecutive case notes of patients started on fibrates in a lipid clinic between 2002 and 2008. Pre- and post-fibrate creatinine concentrations were measured and eGFR measurements were obtained.

Results Of the 79 patients with both pre and post-treatment eGFR values <90 ml/min/1.73 m2, a significant mean eGFR reduction of 8.2 ml/min/1.73 m2 was noted. Of these patients, 50% demonstrated a reduction in eGFR >8 ml/min/1.73 m2, 25% demonstrated a reduction >16 ml/min/1.73 m2, and 10% demonstrated a reduction >21 ml/min/1.73 m2.

Conclusions The authors demonstrate a significant effect of fibrates on eGFR in clinical practice. Awareness of the pattern of eGFR change is important for decisions regarding the continued use of fibrate therapy and/or commonly co-prescribed diabetic drugs and renal specialist referrals.

Source: PMJ/BMJ