| 2008 JASN IMPACT FACTOR 7.505 | HOME AUTHOR INFO EDITORIAL BOARD SUBSCRIBE FEEDBACK ALERTS HELP | |||
| CURRENT ISSUE | ARCHIVES | JASN Express | ONLINE SUBMISSION | |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Clinical Nephrology |




Departments of * Nephrology and Hypertension,
Biostatistics and Epidemiology, and
Cardiothoracic Anesthesiology, Cleveland Clinic Foundation; and
Division of Nephrology and Hypertension, University of Cincinnati Medical Center, Cincinnati, Ohio
Address correspondence to: Dr. Charuhas V. Thakar, Division of Nephrology and Hypertension, University of Cincinnati Medical Center, 231 Albert B. Sabin Way, Cincinnati, OH 45267. Phone: 513-558-4783; Fax: 513-558-4309; E-mail: thakarcv{at}ucmail.uc.edu
| Abstract |
|---|
|
|
|---|
| Introduction |
|---|
|
|
|---|
Prognostic risk stratification is used to predict renal dysfunction and identify patients who are at a greater risk for developing ARF; ARF after open-heart surgery is one of the clinical settings commonly studied in this regard. Although many analyses have identified independent predictors of ARF, relatively few have addressed the issue of preoperative risk stratification (5). These studies, however, either were not well represented by differences in demographic characteristics such as gender and race (5) or excluded high-risk patients (12), thus limiting their clinical utility. Moreover, the studies did not evaluate the simultaneous effect of multiple risk factors on the outcome, by either their order of importance (e.g., odds of outcome) or their degree of stability (e.g., confidence intervals [CI]), which may affect the accuracy of prediction.
The purpose of this analysis was to develop and validate a clinical score that predicts ARF after open-heart surgery. We aimed to develop a scoring model that accurately predicts ARF by accounting for the effect of all of its major risk factors. To achieve adequate power and generalizability, the study aimed to analyze a large cohort of patients that is well represented by differences in gender and race and includes cardiac surgeries with varying degrees of risk, thus making it more clinically applicable. The data indicate that a clinical score is valid in predicting ARF after open-heart surgery and that incorporating the effect of multiple risk factors in the model improves the accuracy of prediction.
| Materials and Methods |
|---|
|
|
|---|
Definitions
The primary outcome was ARF that required dialysis during the postoperative period. The indications for dialysis included uremia, volume overload, or biochemical abnormalities and were based on clinical judgment. We examined the following variables as possible predictors of ARF to develop the scoring model: Age; gender; race; weight; history of congestive heart failure; severe left ventricular dysfunction (ejection fraction <35%); preoperative use of intra-aortic balloon pump; emergency surgery; previous open-heart surgery; history of chronic obstructive pulmonary disease requiring medical therapy; diabetes mellitus; preoperative serum creatinine (mg/dl); cardiopulmonary bypass (CPB) time; and types of cardiac surgery, including coronary artery bypass graft, valve surgery, combined coronary artery bypass graft and valve procedures, and other cardiac surgeries such as ventricular aneurysm repair, pericardiectomy, etc. The rationale for using these variables in the scoring model was based on our previous validation of this database and clinical relevance; a portion of this database (cases from 1993 to 2000) has been validated to identify independent predictors of ARF (8,13). The details regarding the variables included in the database, criteria for exclusion, and definitions of the risk variables and outcomes have been reported previously (8,13). To maintain internal consistency regarding the definitions of risk factors and outcomes for the present study, we chose to use the same definitions as used in our previous analyses.
Statistical Analyses
The scoring model was developed on the test data set (n = 15,838). We compared patients with and without ARF univariably on the risk factors considered for the score using
2, Fisher exact, and t test as appropriate. To select the variables that would be used in the score, we fit logistic regression models for ARF, using stepwise selection to choose the predictors to include in each model in 1000 bootstrapped samples from the test data set (14). We selected variables that were significant predictors of ARF in >50% of the bootstrap runs for the final model. We chose to categorize the continuous predictors of ARF using no more than two cut points for each predictor. To choose these cut points, we used the WinBUGS Gibbs sampling program to estimate and plot the posterior distributions of each cut point. Although CPB time appeared in >50% of the models, we chose not to include it in this scoring model because it is a function of intraoperative course and cannot be determined preoperatively. However, because history of previous open-heart surgery is associated with longer bypass times (data not shown), we chose it as a surrogate marker to represent CPB time in the scoring model. This allows the score to be based exclusively on preoperative risk factors. We then performed a final logistic regression analysis using this reduced set of risk factors. We assigned score points to each risk factor using the model parameter estimates, multiplied by 2 and rounded to the nearest integer. The logistic estimates for the risk variables, corresponding score points, and the contributed area under the curve (AUC) for each variable are shown in Table 1.
|
| Results |
|---|
|
|
|---|
|
|
|
|
|
|
|
| Discussion |
|---|
|
|
|---|
Few studies have addressed this issue. Chertow et al. (5) were among the first to develop a risk algorithm to predict postoperative ARF. This analysis involved a large multicenter cohort of patients (n = 43,642) who underwent cardiac surgery from the Veterans Administration health system. The population was predominantly men (99% men). The risk algorithm was subsequently assessed by Fortescue et al. (12) in a smaller cohort of patients (n = 8797). Although it included a larger proportion of women, this analysis did not include high-risk cardiac surgical procedures such as valve surgery. Both of these analyses excluded patients with severe preoperative renal dysfunction (creatinine >3 mg/dl). We also have analyzed a similar nonparametric recursive partitioning model in our cohort of patients (17). Although these were among the few analyses aimed at risk stratification involving large patient cohorts, there was a limitation in the statistical model that was used. It did not allow testing of the effect of various risk factors by order of their magnitude of association with ARF.
The present analysis includes all of the major risk factors of ARF. The estimates of prediction were subsequently converted into a clinically applicable score. The area under the ROC curve for the ARF score was 0.81 in the test data set and 0.82 in the validation data set. The ROC curve traditionally has been used as a method to describe the intrinsic accuracy of a diagnostic test as well as to compare various diagnostic tests; it can be interpreted as the probability that a randomly selected patient with a disease has a test result indicating greater suspicion of the disease than that of a randomly chosen patient without the disease (15). In other words, when applied to evaluate the accuracy of the ARF score in two randomly selected patientsone with and one without ARFthe probability is 0.82 that the patient with ARF will have a higher score than the patient without ARF. Thus, the present study enhances the accuracy of prediction by accounting for the interaction of all major risk factors by order of their degree of association with postoperative ARF.
In an earlier study, we identified the independent predictors of ARF after open-heart surgery. In addition to confirming the traditional risk factors in a large cohort of patients (n = 24,660), our earlier study identified female gender as an independent risk factor of postoperative ARF (8). The present analysis supplements earlier observations by developing a clinical ARF score that is validated on a randomly selected cohort of patients that was well represented by differences in gender and race. As indicated in Table 4, the frequency of ARF corresponding with each level of the score in the validation data set fell within the 95% CI of the ARF frequency in the test data set. Said in another way, at all levels of risk, the score was valid in predicting ARF when applied to a randomly selected cohort of patients.
A number of studies address the risk for ARF after open-heart surgery. When defined in its most severe form, as requiring dialysis, the reported frequency of postoperative ARF is usually <5% (5,6,18,19). This low event rate translates into two major limitations related to clinical research. First, it limits the ability of most of the epidemiologic studies to identify independent predictors of ARF, as a result of inadequate power (i.e., number of patients). Second, it impedes the development of clinical studies that pertain to early diagnosis and intervention in ARF by necessitating the enrollment of a large number of patients. This underscores the importance of risk stratification in clinical settings where renal injury can be anticipated.
The present study involves a large cohort of patients, sufficient to generate and validate a score that incorporates multiple independent risk factors, despite the low event rate of ARF. Furthermore, we arbitrarily divided the score into four risk categories (Table 4). This allowed optimizing of the number of patients who are at a moderate to high risk for developing ARF and improvement in the clinical utility of the score. The validity of the score was maintained even after the score levels were condensed into four risk categories. The frequency of ARF ranged between 0.4 and 22% across the risk categories. It should be noted that the overall frequency of ARF was 1.8%, so the risk categories allow identification of subgroups of patients who have lower- as well as higher-than-average risk for developing ARF. This can be a valuable tool used to randomize patients in clinical trials of ARF.
A weakness of the present study is that the data are derived from a single center. The model needs to be tested prospectively at multiple centers to substantiate its broad applicability. However, unlike other studies, it does include the single largest cohort of patients that is well represented by differences in gender, race, and all types of cardiac surgical procedures. Inherent to the observational study design is the limitation that it establishes association and not causality. Thus, it would be incorrect to justify a change in clinical decision making regarding open-heart surgery as a result of the risk for ARF on the basis of any such analyses. Nevertheless, it can improve individual patient care by allowing us to identify accurately patients who have a greater likelihood of developing ARF. It should be noted that the proposed scoring model predicts severe form of ARF defined by requirement of dialysis. Although less severe degrees of renal dysfunction (defined arbitrarily) may portend a risk for worse outcomes, the clinically relevant threshold of renal dysfunction after cardiac surgery remains unclear. Our rationale to choose this definition was based on clinical relevance and, more important, because ARF that requires dialysis after cardiac surgery has been unequivocally associated with mortality.
In conclusion, we provide a clinical score validated in our population of patients that predicts ARF after open-heart surgery. The score enhances the accuracy of prediction by accounting for the effect of all major risk factors of ARF. In addition, the score identifies patients who have a lower- as well as a higher-than-average risk for ARF. This increases the clinical utility of the score in improving both individual patient care and by providing a vital tool in planning future clinical trials of early diagnosis and intervention in ARF.
| Acknowledgments |
|---|
| Footnotes |
|---|
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
A. F. Popov, J. Hinz, E. G. Schulz, J. D. Schmitto, C. H. Wiese, M. Quintel, R. Seipelt, and F. A. Schoendube The eNOS 786C/T polymorphism in cardiac surgical patients with cardiopulmonary bypass is associated with renal dysfunction Eur. J. Cardiothorac. Surg., October 1, 2009; 36(4): 651 - 656. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. C. T. Lu, S. G. Coca, U. D. Patel, L. Cantley, C. R. Parikh, and for the Translational Research Investigating Bioma Searching for Genes That Matter in Acute Kidney Injury: A Systematic Review Clin. J. Am. Soc. Nephrol., June 1, 2009; 4(6): 1020 - 1031. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. Anderson, J. B. Halter, W. R. Hazzard, J. Himmelfarb, F. M. Horne, G. A. Kaysen, J. W. Kusek, S. G. Nayfield, K. Schmader, Y. Tian, et al. Prediction, Progression, and Outcomes of Chronic Kidney Disease in Older Adults J. Am. Soc. Nephrol., June 1, 2009; 20(6): 1199 - 1209. [Abstract] [Full Text] [PDF] |
||||
![]() |
C.-y. Hsu, G. M. Chertow, C. E. McCulloch, D. Fan, J. D. Ordonez, and A. S. Go Nonrecovery of Kidney Function and Death after Acute on Chronic Renal Failure Clin. J. Am. Soc. Nephrol., May 1, 2009; 4(5): 891 - 898. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. H. Khan, E. A. Davis, L. S. Dean, M. J. Huff, N. Y. Khan, and A. Rehman The Role of Elective Perioperative Dialysis in Nondialysis Renal Failure Patients Ann. Thorac. Surg., April 1, 2009; 87(4): 1085 - 1089. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. A. Sharfuddin, R. M. Sandoval, D. T. Berg, G. E. McDougal, S. B. Campos, C. L. Phillips, B. E. Jones, A. Gupta, B. W. Grinnell, and B. A. Molitoris Soluble Thrombomodulin Protects Ischemic Kidneys J. Am. Soc. Nephrol., March 1, 2009; 20(3): 524 - 534. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. Karkouti, D. N. Wijeysundera, T. M. Yau, J. L. Callum, D. C. Cheng, M. Crowther, J.-Y. Dupuis, S. E. Fremes, B. Kent, C. Laflamme, et al. Acute Kidney Injury After Cardiac Surgery: Focus on Modifiable Risk Factors Circulation, February 3, 2009; 119(4): 495 - 502. [Abstract] [Full Text] [PDF] |
||||
![]() |
P. Knapik, P. Rozentryt, P. Nadziakiewicz, L. Polonski, and M. Zembala Retrospective cross-validation of simplified predictive index for renal replacement therapy after cardiac surgery Interactive CardioVascular and Thoracic Surgery, December 1, 2008; 7(6): 1101 - 1106. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. Hudson, J. Hudson, M. Swaminathan, A. Shaw, M. Stafford-Smith, and U. D. Patel Emerging Concepts in Acute Kidney Injury Following Cardiac Surgery Seminars in Cardiothoracic and Vascular Anesthesia, December 1, 2008; 12(4): 320 - 330. [Abstract] [PDF] |
||||
![]() |
C. Rosenberger, S. Rosen, A. Shina, U. Frei, K.-U. Eckardt, L. A. Flippin, M. Arend, S. J. Klaus, and S. N. Heyman Activation of hypoxia-inducible factors ameliorates hypoxic distal tubular injury in the isolated perfused rat kidney Nephrol. Dial. Transplant., November 1, 2008; 23(11): 3472 - 3478. [Abstract] [Full Text] [PDF] |
||||
![]() |
U. Benedetto, S. Sciarretta, A. Roscitano, B. Fiorani, S. Refice, E. Angeloni, and R. Sinatra Preoperative Angiotensin-Converting Enzyme Inhibitors and Acute Kidney Injury After Coronary Artery Bypass Grafting Ann. Thorac. Surg., October 1, 2008; 86(4): 1160 - 1165. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. T. Webb and J. S. D. Allen Perioperative renal protection CEACCP, October 1, 2008; 8(5): 176 - 180. [Full Text] [PDF] |
||||
![]() |
J. Granton and D. Cheng Risk Stratification Models for Cardiac Surgery Seminars in Cardiothoracic and Vascular Anesthesia, September 1, 2008; 12(3): 167 - 174. [Abstract] [PDF] |
||||
![]() |
A. Candela-Toha, E. Elias-Martin, V. Abraira, M. T. Tenorio, D. Parise, A. de Pablo, T. Centella, and F. Liano Predicting Acute Renal Failure after Cardiac Surgery: External Validation of Two New Clinical Scores Clin. J. Am. Soc. Nephrol., September 1, 2008; 3(5): 1260 - 1265. [Abstract] [Full Text] [PDF] |
||||
![]() |
P. Arora, S. Rajagopalam, R. Ranjan, H. Kolli, M. Singh, R. Venuto, and J. Lohr Preoperative Use of Angiotensin-Converting Enzyme Inhibitors/Angiotensin Receptor Blockers Is Associated with Increased Risk for Acute Kidney Injury after Cardiovascular Surgery Clin. J. Am. Soc. Nephrol., September 1, 2008; 3(5): 1266 - 1273. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. R. Brown, R. P. Cochran, T. A. MacKenzie, A. P. Furnary, K. S. Kunzelman, C. S. Ross, C. W. Langner, D. C. Charlesworth, B. J. Leavitt, L. J. Dacey, et al. Long-Term Survival After Cardiac Surgery is Predicted by Estimated Glomerular Filtration Rate Ann. Thorac. Surg., July 1, 2008; 86(1): 4 - 11. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. Haase, A. Haase-Fielitz, S. Ratnaike, M. C. Reade, S. M. Bagshaw, S. Morgera, D. Dragun, and R. Bellomo N-Acetylcysteine does not artifactually lower plasma creatinine concentration Nephrol. Dial. Transplant., May 1, 2008; 23(5): 1581 - 1587. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. Bennett, C. L. Dent, Q. Ma, S. Dastrala, F. Grenier, R. Workman, H. Syed, S. Ali, J. Barasch, and P. Devarajan Urine NGAL Predicts Severity of Acute Kidney Injury After Cardiac Surgery: A Prospective Study Clin. J. Am. Soc. Nephrol., May 1, 2008; 3(3): 665 - 673. [Abstract] [Full Text] [PDF] |
||||
![]() |
H.-Y. Yu, J.-Y. Li, S. Sun, K.-Y. Hung, J.-L. Wang, Y.-S. Chen, S.-S. Wang, and F.-Y. Lin Late dialysis rate for coronary artery bypass grafting patients with moderate-to-severe renal impairment: comparison between off-pump and conventional method Eur. J. Cardiothorac. Surg., March 1, 2008; 33(3): 364 - 369. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. H. Rosner, D. Portilla, and M. D. Okusa Analytic Reviews: Cardiac Surgery as a Cause of Acute Kidney Injury: Pathogenesis and Potential Therapies J Intensive Care Med, January 1, 2008; 23(1): 3 - 18. [Abstract] [PDF] |
||||
![]() |
D. Del Duca, S. Iqbal, E. Rahme, P. Goldberg, and B. de Varennes Renal Failure After Cardiac Surgery: Timing of Cardiac Catheterization and Other Perioperative Risk Factors Ann. Thorac. Surg., October 1, 2007; 84(4): 1264 - 1271. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. P. Furnary, Y. Wu, L. F. Hiratzka, G. L. Grunkemeier, and U. S. Page 3rd Aprotinin Does Not Increase the Risk of Renal Failure in Cardiac Surgery Patients Circulation, September 11, 2007; 116(11_suppl): I-127 - I-133. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. R. Brown, R. P. Cochran, B. J. Leavitt, L. J. Dacey, C. S. Ross, T. A. MacKenzie, K. S. Kunzelman, R. S. Kramer, F. Hernandez Jr, R. E. Helm, et al. Multivariable Prediction of Renal Insufficiency Developing After Cardiac Surgery Circulation, September 11, 2007; 116(11_suppl): I-139 - I-143. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. Simon, R. Luciani, F. Capuano, A. Miceli, A. Roscitano, E. Tonelli, and R. Sinatra Mild and moderate renal dysfunction: impact on short-term outcome Eur. J. Cardiothorac. Surg., August 1, 2007; 32(2): 286 - 290. [Abstract] [Full Text] [PDF] |
||||
![]() |
K. Doddakula, N. Al-Sarraf, K. Gately, A. Hughes, M. Tolan, V. Young, and E. McGovern Predictors of acute renal failure requiring renal replacement therapy post cardiac surgery in patients with preoperatively normal renal function Interactive CardioVascular and Thoracic Surgery, June 1, 2007; 6(3): 314 - 318. [Abstract] [Full Text] [PDF] |
||||
![]() |
D. N. Wijeysundera, K. Karkouti, J.-Y. Dupuis, V. Rao, C. T. Chan, J. T. Granton, and W. S. Beattie Derivation and Validation of a Simplified Predictive Index for Renal Replacement Therapy After Cardiac Surgery JAMA, April 25, 2007; 297(16): 1801 - 1809. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. Aronson, M. L. Fontes, Y. Miao, D. T. Mangano, and for the Investigators of the Multicenter Study of Risk Index for Perioperative Renal Dysfunction/Failure: Critical Dependence on Pulse Pressure Hypertension Circulation, February 13, 2007; 115(6): 733 - 742. [Abstract] [Full Text] [PDF] |
||||
![]() |
L. S. Chawla, M. G. Seneff, D. R. Nelson, M. Williams, H. Levy, P. L. Kimmel, and W. L. Macias Elevated Plasma Concentrations of IL-6 and Elevated APACHE II Score Predict Acute Kidney Injury in Patients with Severe Sepsis Clin. J. Am. Soc. Nephrol., January 1, 2007; 2(1): 22 - 30. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. B. Yates and M. Stafford-Smith The genetic determinants of renal impairment following cardiac surgery. Seminars in Cardiothoracic and Vascular Anesthesia, December 1, 2006; 10(4): 314 - 326. [Abstract] [PDF] |
||||
![]() |
Y. Abu-Omar and C. Ratnatunga Cardiopulmonary Bypass and Renal Injury Perfusion, July 1, 2006; 21(4): 209 - 213. [Abstract] [PDF] |
||||
![]() |
S. Basran, R. J. Frumento, A. Cohen, S. Lee, Y. Du, E. Nishanian, H. S. Kaplan, M. Stafford-Smith, and E. Bennett-Guerrero The association between duration of storage of transfused red blood cells and morbidity and mortality after reoperative cardiac surgery. Anesth. Analg., July 1, 2006; 103(1): 15 - 20. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. H. Rosner and M. D. Okusa Acute Kidney Injury Associated with Cardiac Surgery Clin. J. Am. Soc. Nephrol., January 1, 2006; 1(1): 19 - 32. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
HOME
CURRENT ISSUE
ARCHIVES
JASN Express
ONLINE SUBMISSION
AUTHOR INFO
EDITORIAL BOARD SUBSCRIBE FEEDBACK ALERTS HELP |