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Acute Renal Failure |
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* Center for Health Equity Research and Promotion and
Renal Section, Medical Specialty Service Line, VA Pittsburgh Healthcare System, Pittsburgh, Pennsylvania;
Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania;
Department of Biostatistics, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania; and || Division of General Internal Medicine, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
Address correspondence to: Dr. Steven D. Weisbord, VA Pittsburgh Healthcare System, Mailstop 111F-U, 7E Room 120, Pittsburgh, PA 15240. Phone: 412-688-6000, x815911; Fax: 412-688-6908; E-mail: weisbordsd{at}upmc.edu
| Abstract |
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Design, setting, participants, & measurements: Patients with estimated glomerular filtration rates (GFRs) <60 ml/min per 1.73 m2 undergoing nonemergent computed tomography with intravenous iodinated radiocontrast at an academic VA Medical Center were prospectively identified. Serum creatinine was assessed 48 to 96 h postprocedure to quantify the incidence of CIAKI, and the need for postprocedure dialysis, hospital admission, and 30-d mortality was tracked to examine the associations of CIAKI with these medical outcomes.
Results: A total of 421 patients with a median estimated GFR of 53 ml/min per 1.73 m2 were enrolled. Overall, 6.5% of patients developed an increase in serum creatinine
25%, and 3.5% demonstrated a rise in serum creatinine
0.5 mg/dl. Although only 6% of outpatients received preprocedure and postprocedure intravenous fluid, <1% of outpatients with estimated GFRs >45 ml/min per 1.73 m2 manifested an increase in serum creatinine
0.5 mg/dl. None of the study participants required postprocedure dialysis. Forty-six patients (10.9%) were hospitalized and 10 (2.4%) died by 30-d follow-up; however, CIAKI was not associated with these outcomes.
Conclusions: Clinically significant CIAKI following nonemergent computed tomography is uncommon among outpatients with mild baseline kidney disease. These findings have important implications for providers ordering and performing computed tomography and for future clinical trials of CIAKI.
| Introduction |
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A large proportion of patients who receive intravascular iodinated contrast do so when undergoing outpatient computed tomography. The routine assessment of risk status and implementation of preventive interventions, such as IV fluid, are considerably more difficult in patients who undergo elective computed tomography than coronary angiography. The practical and fiscal challenges to systematically administering preprocedure and postprocedure IV fluid to "at risk" patients are substantial, particularly in the outpatient setting. However, to determine the most effective and practical approach to identifying patients at increased risk for CIAKI following computed tomography and implementing preventive care to those most likely to derive benefit, greater clarity is needed on the incidence and clinical sequelae of CIAKI in this patient population. The primary aim of this study was to assess the incidence and outcomes of CIAKI following nonemergent computed tomography in the inpatient and outpatient setting.
| Materials and Methods |
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Radiology personnel approached eligible subjects at the time of the procedure to introduce the study. For interested patients, a study coordinator explained the study in detail and obtained informed consent.
Baseline Data Collection
We collected demographic data from patients and asked about current use of prescribed or over-the-counter NSAIDs other than once-daily aspirin. We asked patients taking NSAIDs if they were instructed to discontinue the medication before the procedure, and if so, whether they complied. The study coordinator also asked patients whether they were instructed to increase their oral fluid intake in advance of the procedure, and if so, whether they did so. We also recorded the type and volume of contrast media administered and treatment location at the time of the procedure (inpatient versus outpatient). Patients residing at a nursing facility were considered inpatients. For patients undergoing outpatient procedures, arrangements were made for a Scr to be measured at a VA laboratory 48 to 96 h following the procedure. Although we aimed to have this test performed approximately 48 h following all outpatient procedures, we extended this window to 96 h because VA laboratory facilities are not open on weekends. For inpatients, we ordered a 48-h postprocedure Scr and recorded all postprocedure Scr measurements performed in the hospital.
Using the electronic medical record, we identified all prescription medications and comorbid medical conditions, including diabetes mellitus, congestive heart failure, liver disease, and cerebral, peripheral, and/or coronary vascular disease. This electronic medical record review also included an assessment of the use of periprocedure IV fluid and NAC. Of note, there was no formal protocol for the prevention of CIAKI at our institution at the time of this study.
Follow-up Data Collection
To evaluate medical outcomes associated with CIAKI, we conducted 30-d medical record reviews and telephone interviews to determine vital status, whether postprocedure dialysis was required, and hospital admissions not including those immediately following the index computed tomography scan. The medical record review was based on a comprehensive assessment of the integrated VA electronic health record that captures all visits, hospitalizations, and procedures at any VA facility nationwide. The review of hospitalizations included an assessment of whether the admission was the result of kidney disease. As a safety precaution, we performed a repeat Scr in all outpatients who manifested a postprocedure rise in Scr
25% to ensure that progressive renal failure did not develop.
Statistical Analyses
Our primary analyses were based on assessing the incidence of CIAKI and the associations of CIAKI with 30-d outcomes in the overall study population, and among subgroups of patients defined by location at the time of the procedure (inpatient versus outpatient) and baseline eGFR (
or >45 ml/min per 1.73 m2). Because there is no consensus on the most valid definition of CIAKI, we evaluated the incidence of this condition using three nonmutually exclusive definitions based on relative increases in Scr from baseline (
25%,
50%, and
100%) and three absolute increments in Scr from baseline (
0.25 mg/dl,
0.5 mg/dl, and
1.0 mg/dl). We also assessed the incidence of CIAKI based on the RIFLE criteria, which defines acute kidney injury based on 5 distinct categories: Risk, Injury, Failure, Loss, and End-stage kidney disease. Because we did not collect urine output data, these assessments were based solely on changes in Scr. Among hospitalized patients with multiple postprocedure Scr measurements, the development of CIAKI was determined by the maximal change in Scr within 96 h.
Differences in patient characteristics, use of preventive care, and the incidence of CIAKI between outpatients and inpatients were assessed using t test, Fisher exact, and
2 tests, as appropriate. Unadjusted associations of CIAKI with 30-d mortality, need for dialysis, and hospitalization were assessed using the Fisher exact test for each of the definitions of CIAKI. Because of the very low incidence of death, we used exact logistic regression to examine the independent association of CIAKI with 30-d mortality, adjusting for potentially confounding covariates that were found to have univariate associations (P
0.10) with this outcome. A two-sided P value of <0.05 was considered to represent statistical significance. All analyses were conducted using STATA version 9 (College Station, TX).
| Results |
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Incidence and Predictors of CIAKI
A total of 367 patients (87%) had postprocedure Scr measured. The incidence of CIAKI varied from 0% to 6.5% based on relative increases in Scr of
100% to
25%, respectively, and from 0.3% to 10.9% with absolute increments in Scr of
1.0 mg/dl to 0.25 mg/dl, respectively. Only 2 patients (0.5%) met criteria for the RISK stage of acute kidney injury (increase in Scr times 1.5) using the RIFLE definition. None of the patients met criteria for more advanced RIFLE stages. CIAKI was more common among patients with baseline eGFR
45 ml/min per 1.73 m2. Among subjects with eGFR >45 ml/min per 1.73 m2, CIAKI was considerably more common in hospitalized patients (Table 3). All outpatients with a postprocedure rise in Scr
25% had a repeat Scr performed, and none developed more advanced renal insufficiency.
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25% and an increase
0.5 mg/dl, are depicted in Table 4. Congestive heart failure, baseline Scr >1.5 mg/dl, and inpatient status were associated with an increased risk of CIAKI (P < 0.05). Baseline eGFR
45 ml/min per 1.73 m2 was associated with increased risk of CIAKI defined by an increase in Scr
0.5 mg/dl. Use of >100 ml of contrast was associated with increased risk of CIAKI defined by a rise in Scr
25%. There was a slight trend toward a lower risk for CIAKI, defined by an increase in Scr
25%, with Iodixanol compared with Iohexol (odds ratio = 0.5, P = 0.14), although this difference did not meet the level of statistical significance. No difference in risk for CIAKI, defined by a rise in Scr
0.5 mg/dl, was seen between the two contrast agents. The administration of IV fluids and use of NAC were not associated with a decreased incidence of CIAKI, although patients who received these preventive interventions were considerably more likely to be hospitalized at the time of their procedure and to have lower eGFR, making them a much higher risk group.
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None of the definitions of CIAKI was associated with an increased risk for 30-d mortality in either univariate or multivariable analyses, as the 95% confidence intervals of all odds ratios crossed one (Table 5). CIAKI was not associated with a need for dialysis as none of the study participants required renal replacement therapy following the procedure. Similarly, none of the six definitions of CIAKI was associated with an increased risk for hospital admission (data not shown).
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| Discussion |
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The overall incidence of CIAKI in the present study is consistent with that observed in recent clinical trials of patients undergoing computed tomography (21,22). Our results build upon prior studies by describing the very low risk for CIAKI among outpatients with mild kidney disease. These findings are particularly noteworthy considering that preprocedure and/or postprocedure IV fluids were not administered to most outpatients. Only 3.8% of our patients who underwent outpatient procedures with a baseline eGFR >45 ml/min per 1.73 m2 received preprocedure and postprocedure IV fluid, yet less than 2.5% developed CIAKI. There are significant challenges to the routine use of intravascular volume expansion in patients undergoing contrast-enhanced outpatient computed tomography. Most radiology suites are not adequately equipped or staffed to administer IV fluids, and most insurers do not authorize routine hospital admission for this purpose. However, the very low incidence of CIAKI among outpatients with only mildly reduced eGFR in the current study, less than 4% of whom received preprocedure and postprocedure IV fluids, suggests that the use of intravascular volume expansion may not be routinely necessary in this patient group and may be better reserved for hospitalized patients and outpatients with more advanced baseline renal insufficiency. Indeed, patients who were hospitalized or had lower baseline eGFR levels in our study were more likely to receive preventive interventions for CIAKI and were seemingly more likely to derive benefit from such care.
Although biochemically defined CIAKI was not uncommon in our study population, serious adverse outcomes were rare. None of our patients required dialysis, and there were no associations of CIAKI with need for hospital admission or death at 30 d. In a recent study of 153 patients with chronic kidney disease undergoing contrast-enhanced multidetector computed tomography, CIAKI did not necessitate renal replacement therapy or hospitalization (21). Collectively, our results and the findings of this recent clinical trial suggest that that biochemical evidence of CIAKI in clinically stable patients is not synonymous with clinically significant renal failure.
In addition to providing a scientific basis from which providers will be able to make evidence-based decisions on the risk for CIAKI and need to implement preventive measures, our findings have important research implications. Some past studies have used relatively small increments in Scr as surrogate markers for clinically relevant CIAKI. However, only 2 patients (0.5%) in our study met criteria for the RISK stage of kidney injury using the RIFLE criteria, and none manifested more advanced kidney injury. This suggests that the use of small changes in Scr to estimate sample size requirements, although helping to ensure a sufficient number of primary study "events," likely results in inadequate power to assess clinically meaningful outcomes (23–28). We conducted post hoc analyses to determine the sample size requirements of a clinical trial testing a hypothetical intervention that would reduce the incidence of CIAKI, from 3.5%, which was the incidence in our study using a definition of an increase in Scr
0.5 mg/dl, to 1.75%. Using a type I error of 5% and 80% power, 1393 patients would be needed in each study arm to accurately assess the efficacy of the intervention. A substantially larger study population would be required to detect meaningful differences in outcomes such as death. To date, most studies of CIAKI have enrolled substantially smaller numbers of patients, which has likely confounded efforts to assess the efficacy of preventive interventions for the highest-risk patients. In designing future clinical trials of CIAKI in the setting of computed tomography, investigators should seek to enroll a larger number of high-risk patients and consider incorporating outcomes, such as need for dialysis and/or death in sample size estimates.
There are two potential explanations for the low incidence of CIAKI among outpatients in the present study. First, 254 patients initially scheduled for contrast-enhanced procedures did not receive IV contrast. The median eGFR of these patients was 9 ml/min per 1.73 m2 lower than study participants. Although we did not record reasons for the nonuse of IV contrast, perceived risk for CIAKI by radiologists is the likely explanation. Unlike with angiography, computed tomography can be performed without IV contrast. However, for certain indications, diagnostic accuracy decreases without vascular enhancement. Cost-benefit analyses that weigh the short-term advantage of avoiding CIAKI with noncontrast studies with the longer-term risk of failing to diagnose specific conditions will be needed in patients at high risk for CIAKI. Moreover, efforts to delineate the eGFR level below which the risk for clinically consequential CIAKI rises are needed to help inform a practical and feasible approach to implementing preventive care. Our observation that baseline eGFR is a primary driver of the implementation of preventive care underscores the importance of identifying such a threshold. Second, most outpatients (90%) received iso-osmolal Iodixanol, which has been shown in some studies to be less nephrotoxic than low-osmolal Iohexol (29–31). It is plausible that the use of less nephrotoxic contrast media among outpatients with only mildly reduced kidney function provides sufficient protection against CIAKI.
This study has certain limitations. First, our sample size was relatively small; and because many patients had only mildly reduced eGFR and were undergoing nonemergent procedures, our results are not generalizable to higher-risk populations or to patients undergoing sequential procedures with contrast. Second, this was a single-center study, which limits the external validity of our findings. Third, a moderate number of patients were unavailable to provide consent or refused to participate, which reduced the size of evaluable patients. Fourth, there was considerable variability in the timing of postprocedure Scr assessments, and inpatients were more likely to have multiple postprocedure Scr assessments, which could have confounded our assessment of the incidence of CIAKI and comparisons between inpatients and outpatients. However, our evaluation of 30-d outcomes makes up for this limitation by demonstrating that clinically relevant patient outcomes were extremely rare, irrespective of timing of postprocedure Scr measurements. Fifth, although a minority of our patients received IV fluids or NAC, the use of these interventions in approximately 20% of patients, along with the use of iso-osmolal contrast in most subjects, may have contributed to the low incidence of CIAKI. Sixth, the use of a single preprocedure Scr value to estimate baseline kidney function did not allow us to confirm that abnormal values represented chronic and not acute kidney disease. Lastly, we were unable to determine 30-d outcomes by phone interview in a modest number of patients. However, because all of our patients were receiving care in the VA, which has an integrated electronic medical record that captures patient events at all VA facilities, we likely identified most 30-d outcomes by medical record review alone.
| Conclusions |
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| Disclosures |
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| Acknowledgments |
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| Footnotes |
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See related editorial, "Contrast-Induced Acute Kidney Injury: Is There a Risk after Intravenous Contrast?" on pages 1242–1243.
Received March 17, 2008. Accepted April 11, 2008.
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