Acute Kidney Injury: A Relevant Complication After Cardiac Surgery
2011; Elsevier BV; Volume: 92; Issue: 4 Linguagem: Inglês
10.1016/j.athoracsur.2011.04.123
ISSN1552-6259
AutoresGiovanni Mariscalco, Roberto Lorusso, Carmelo Dominici, Attilio Renzulli, Andrea Sala,
Tópico(s)Cardiac Ischemia and Reperfusion
ResumoAcute kidney injury (AKI) occurs in as many as 40% of patients after cardiac surgery and requires dialysis in 1% of cases. Acute kidney injury is associated with an increased risk of mortality and morbidity, predisposes patients to a longer hospitalization, requires additional treatments, and increases the hospital costs. Acute kidney injury is characterized by a progressive worsening course, being the consequence of an interplay of different pathophysiologic mechanisms, with patient-related factors and cardiopulmonary bypass as major causes. Recently, several novel biomarkers have emerged, showing reasonable sensitivity and specificity for AKI prediction and protection. The development and implementation of potentially protective therapies for AKI remains essential, especially for the relevant impact of AKI on early and late survival. Acute kidney injury (AKI) occurs in as many as 40% of patients after cardiac surgery and requires dialysis in 1% of cases. Acute kidney injury is associated with an increased risk of mortality and morbidity, predisposes patients to a longer hospitalization, requires additional treatments, and increases the hospital costs. Acute kidney injury is characterized by a progressive worsening course, being the consequence of an interplay of different pathophysiologic mechanisms, with patient-related factors and cardiopulmonary bypass as major causes. Recently, several novel biomarkers have emerged, showing reasonable sensitivity and specificity for AKI prediction and protection. The development and implementation of potentially protective therapies for AKI remains essential, especially for the relevant impact of AKI on early and late survival. Despite ongoing efforts to decrease its occurrence, acute kidney injury (AKI) remains a frequent complication of cardiac surgery [1Chertow G.M. Lazarus J.M. Christiansen C.L. et al.Preoperative renal risk stratification.Circulation. 1997; 95: 878-884Crossref PubMed Scopus (666) Google Scholar, 2Chertow G.M. Burdick E. Honour M. Bonventre J.V. Bates D.W. Acute kidney injury, mortality, length of stay, and costs in hospitalized patients.J Am Soc Nephrol. 2005; 16: 3365-3370Crossref PubMed Scopus (2549) Google Scholar, 3Karkouti K. Wijeysundera D.N. Yau T.M. et al.Acute kidney injury after cardiac surgery: focus on modifiable risk factors.Circulation. 2009; 119: 495-502Crossref PubMed Scopus (547) Google Scholar, 4Wijeysundera D.N. Karkouti K. Dupuis J.Y. et al.Derivation and validation of a simplified predictive index for renal replacement therapy after cardiac surgery.JAMA. 2007; 297: 1801-1809Crossref PubMed Scopus (328) Google Scholar, 5Thakar C.V. Arrigain S. Worley S. Yared J.P. Paganini E.P. A clinical score to predict acute renal failure after cardiac surgery.J Am Soc Nephrol. 2005; 16: 162-168Crossref PubMed Scopus (769) Google Scholar, 6Mehta R.H. Grab J.D. O'Brien S.M. et al.Bedside tool for predicting the risk of postoperative dialysis in patients undergoing cardiac surgery.Circulation. 2006; 114: 2208-2216Crossref PubMed Scopus (422) Google Scholar, 7Palomba H. de Castro I. Neto A.L. Lage S. Yu L. Acute kidney injury prediction following elective cardiac surgery: AKICS score.Kidney Int. 2007; 72: 624-631Crossref PubMed Scopus (253) Google Scholar, 8Brown J.R. Cochran R.P. Leavitt B.J. et al.Multivariable prediction of renal insufficiency developing after cardiac surgery.Circulation. 2007; 116: I139-I143Crossref PubMed Scopus (123) Google Scholar, 9Coca S.G. Yusuf B. Shlipak M.G. Garg A.X. Parikh C.R. Long-term risk of mortality and other adverse outcomes after acute kidney injury: a systematic review and meta-analysis.Am J Kidney Dis. 2009; 53: 961-973Abstract Full Text Full Text PDF PubMed Scopus (835) Google Scholar, 10Aronson S. Fontes M.L. Miao Y. Mangano D.T. Risk index for perioperative renal dysfunction/failure: critical dependence on pulse pressure hypertension.Circulation. 2007; 115: 733-742Crossref PubMed Scopus (183) Google Scholar, 11Brown J.R. Kramer R.S. Coca S.G. Parikh C.R. Duration of acute kidney injury impacts long-term survival after cardiac surgery.Ann Thorac Surg. 2010; 90: 1142-1148Abstract Full Text Full Text PDF PubMed Scopus (250) Google Scholar, 12Arnaoutakis G.J. Bihorac A. Martin T.D. et al.RIFLE criteria for acute kidney injury in aortic arch surgery.J Thorac Cardiovasc Surg. 2007; 134: 1554-1560Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar, 13Hobson C.E. Yavas S. Segal M.S. et al.Acute kidney injury is associated with increased long-term mortality after cardiothoracic surgery.Circulation. 2009; 119: 2444-2453Crossref PubMed Scopus (718) Google Scholar, 14Mangano C.M. Diamondstone L.S. Ramsay J.G. Aggarwal A. Herskowitz A. Mangano D.T. Renal dysfunction after myocardial revascularization: risk factors, adverse outcomes, and hospital resource utilization The Multicenter Study of Perioperative Ischemia Research Group.Ann Intern Med. 1998; 128: 194-203Crossref PubMed Scopus (931) Google Scholar, 15Rosner M.H. Okusa M.D. Acute kidney injury associated with cardiac surgery.Clin J Am Soc Nephrol. 2006; 1: 19-32Crossref PubMed Scopus (828) Google Scholar]. Its incidence varies depending on the adopted definitions, the mode of detection, and the clinical profile of the analyzed patients [1Chertow G.M. Lazarus J.M. Christiansen C.L. et al.Preoperative renal risk stratification.Circulation. 1997; 95: 878-884Crossref PubMed Scopus (666) Google Scholar, 2Chertow G.M. Burdick E. Honour M. Bonventre J.V. Bates D.W. Acute kidney injury, mortality, length of stay, and costs in hospitalized patients.J Am Soc Nephrol. 2005; 16: 3365-3370Crossref PubMed Scopus (2549) Google Scholar, 3Karkouti K. Wijeysundera D.N. Yau T.M. et al.Acute kidney injury after cardiac surgery: focus on modifiable risk factors.Circulation. 2009; 119: 495-502Crossref PubMed Scopus (547) Google Scholar, 4Wijeysundera D.N. Karkouti K. Dupuis J.Y. et al.Derivation and validation of a simplified predictive index for renal replacement therapy after cardiac surgery.JAMA. 2007; 297: 1801-1809Crossref PubMed Scopus (328) Google Scholar, 5Thakar C.V. Arrigain S. Worley S. Yared J.P. Paganini E.P. A clinical score to predict acute renal failure after cardiac surgery.J Am Soc Nephrol. 2005; 16: 162-168Crossref PubMed Scopus (769) Google Scholar, 6Mehta R.H. Grab J.D. O'Brien S.M. et al.Bedside tool for predicting the risk of postoperative dialysis in patients undergoing cardiac surgery.Circulation. 2006; 114: 2208-2216Crossref PubMed Scopus (422) Google Scholar, 7Palomba H. de Castro I. Neto A.L. Lage S. Yu L. Acute kidney injury prediction following elective cardiac surgery: AKICS score.Kidney Int. 2007; 72: 624-631Crossref PubMed Scopus (253) Google Scholar, 8Brown J.R. Cochran R.P. Leavitt B.J. et al.Multivariable prediction of renal insufficiency developing after cardiac surgery.Circulation. 2007; 116: I139-I143Crossref PubMed Scopus (123) Google Scholar, 9Coca S.G. Yusuf B. Shlipak M.G. Garg A.X. Parikh C.R. Long-term risk of mortality and other adverse outcomes after acute kidney injury: a systematic review and meta-analysis.Am J Kidney Dis. 2009; 53: 961-973Abstract Full Text Full Text PDF PubMed Scopus (835) Google Scholar, 10Aronson S. Fontes M.L. Miao Y. Mangano D.T. Risk index for perioperative renal dysfunction/failure: critical dependence on pulse pressure hypertension.Circulation. 2007; 115: 733-742Crossref PubMed Scopus (183) Google Scholar, 11Brown J.R. Kramer R.S. Coca S.G. Parikh C.R. Duration of acute kidney injury impacts long-term survival after cardiac surgery.Ann Thorac Surg. 2010; 90: 1142-1148Abstract Full Text Full Text PDF PubMed Scopus (250) Google Scholar, 12Arnaoutakis G.J. Bihorac A. Martin T.D. et al.RIFLE criteria for acute kidney injury in aortic arch surgery.J Thorac Cardiovasc Surg. 2007; 134: 1554-1560Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar, 13Hobson C.E. Yavas S. Segal M.S. et al.Acute kidney injury is associated with increased long-term mortality after cardiothoracic surgery.Circulation. 2009; 119: 2444-2453Crossref PubMed Scopus (718) Google Scholar, 14Mangano C.M. Diamondstone L.S. Ramsay J.G. Aggarwal A. Herskowitz A. Mangano D.T. Renal dysfunction after myocardial revascularization: risk factors, adverse outcomes, and hospital resource utilization The Multicenter Study of Perioperative Ischemia Research Group.Ann Intern Med. 1998; 128: 194-203Crossref PubMed Scopus (931) Google Scholar, 15Rosner M.H. Okusa M.D. Acute kidney injury associated with cardiac surgery.Clin J Am Soc Nephrol. 2006; 1: 19-32Crossref PubMed Scopus (828) Google Scholar]. Therefore, the incidence of AKI is different across studies, occurring in 1% to 30% of the patients when defined broadly, whereas frequency of AKI requiring dialysis is generally lower, ranging between less than 1% and 6% [1Chertow G.M. Lazarus J.M. Christiansen C.L. et al.Preoperative renal risk stratification.Circulation. 1997; 95: 878-884Crossref PubMed Scopus (666) Google Scholar, 2Chertow G.M. Burdick E. Honour M. Bonventre J.V. Bates D.W. Acute kidney injury, mortality, length of stay, and costs in hospitalized patients.J Am Soc Nephrol. 2005; 16: 3365-3370Crossref PubMed Scopus (2549) Google Scholar, 3Karkouti K. Wijeysundera D.N. Yau T.M. et al.Acute kidney injury after cardiac surgery: focus on modifiable risk factors.Circulation. 2009; 119: 495-502Crossref PubMed Scopus (547) Google Scholar, 4Wijeysundera D.N. Karkouti K. Dupuis J.Y. et al.Derivation and validation of a simplified predictive index for renal replacement therapy after cardiac surgery.JAMA. 2007; 297: 1801-1809Crossref PubMed Scopus (328) Google Scholar, 5Thakar C.V. Arrigain S. Worley S. Yared J.P. Paganini E.P. A clinical score to predict acute renal failure after cardiac surgery.J Am Soc Nephrol. 2005; 16: 162-168Crossref PubMed Scopus (769) Google Scholar, 6Mehta R.H. Grab J.D. O'Brien S.M. et al.Bedside tool for predicting the risk of postoperative dialysis in patients undergoing cardiac surgery.Circulation. 2006; 114: 2208-2216Crossref PubMed Scopus (422) Google Scholar, 7Palomba H. de Castro I. Neto A.L. Lage S. Yu L. Acute kidney injury prediction following elective cardiac surgery: AKICS score.Kidney Int. 2007; 72: 624-631Crossref PubMed Scopus (253) Google Scholar, 8Brown J.R. Cochran R.P. Leavitt B.J. et al.Multivariable prediction of renal insufficiency developing after cardiac surgery.Circulation. 2007; 116: I139-I143Crossref PubMed Scopus (123) Google Scholar, 9Coca S.G. Yusuf B. Shlipak M.G. Garg A.X. Parikh C.R. Long-term risk of mortality and other adverse outcomes after acute kidney injury: a systematic review and meta-analysis.Am J Kidney Dis. 2009; 53: 961-973Abstract Full Text Full Text PDF PubMed Scopus (835) Google Scholar, 10Aronson S. Fontes M.L. Miao Y. Mangano D.T. Risk index for perioperative renal dysfunction/failure: critical dependence on pulse pressure hypertension.Circulation. 2007; 115: 733-742Crossref PubMed Scopus (183) Google Scholar, 11Brown J.R. Kramer R.S. Coca S.G. Parikh C.R. Duration of acute kidney injury impacts long-term survival after cardiac surgery.Ann Thorac Surg. 2010; 90: 1142-1148Abstract Full Text Full Text PDF PubMed Scopus (250) Google Scholar, 12Arnaoutakis G.J. Bihorac A. Martin T.D. et al.RIFLE criteria for acute kidney injury in aortic arch surgery.J Thorac Cardiovasc Surg. 2007; 134: 1554-1560Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar, 13Hobson C.E. Yavas S. Segal M.S. et al.Acute kidney injury is associated with increased long-term mortality after cardiothoracic surgery.Circulation. 2009; 119: 2444-2453Crossref PubMed Scopus (718) Google Scholar, 14Mangano C.M. Diamondstone L.S. Ramsay J.G. Aggarwal A. Herskowitz A. Mangano D.T. Renal dysfunction after myocardial revascularization: risk factors, adverse outcomes, and hospital resource utilization The Multicenter Study of Perioperative Ischemia Research Group.Ann Intern Med. 1998; 128: 194-203Crossref PubMed Scopus (931) Google Scholar, 15Rosner M.H. Okusa M.D. Acute kidney injury associated with cardiac surgery.Clin J Am Soc Nephrol. 2006; 1: 19-32Crossref PubMed Scopus (828) Google Scholar]. The incidence of AKI is certainly influenced by the type of cardiac operation [1Chertow G.M. Lazarus J.M. Christiansen C.L. et al.Preoperative renal risk stratification.Circulation. 1997; 95: 878-884Crossref PubMed Scopus (666) Google Scholar, 2Chertow G.M. Burdick E. Honour M. Bonventre J.V. Bates D.W. Acute kidney injury, mortality, length of stay, and costs in hospitalized patients.J Am Soc Nephrol. 2005; 16: 3365-3370Crossref PubMed Scopus (2549) Google Scholar, 3Karkouti K. Wijeysundera D.N. Yau T.M. et al.Acute kidney injury after cardiac surgery: focus on modifiable risk factors.Circulation. 2009; 119: 495-502Crossref PubMed Scopus (547) Google Scholar, 4Wijeysundera D.N. Karkouti K. Dupuis J.Y. et al.Derivation and validation of a simplified predictive index for renal replacement therapy after cardiac surgery.JAMA. 2007; 297: 1801-1809Crossref PubMed Scopus (328) Google Scholar, 6Mehta R.H. Grab J.D. O'Brien S.M. et al.Bedside tool for predicting the risk of postoperative dialysis in patients undergoing cardiac surgery.Circulation. 2006; 114: 2208-2216Crossref PubMed Scopus (422) Google Scholar]. Typically, patients undergoing coronary artery bypass graft surgery (CABG) present the lowest incidence (2% to 5%), whereas patients undergoing valvular or combined procedures show a higher rate (as high as 30%) [16]. Similarly, AKI after transcatheter aortic valve implantation is registered in approximately 10% of the patients, whereas after complex operations such as aortic surgery for aneurysm repair or aortic dissection, incidences of AKI have been reported at 10% to 50% [12Arnaoutakis G.J. Bihorac A. Martin T.D. et al.RIFLE criteria for acute kidney injury in aortic arch surgery.J Thorac Cardiovasc Surg. 2007; 134: 1554-1560Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar, 13Hobson C.E. Yavas S. Segal M.S. et al.Acute kidney injury is associated with increased long-term mortality after cardiothoracic surgery.Circulation. 2009; 119: 2444-2453Crossref PubMed Scopus (718) Google Scholar, 17Bagur R. Webb J.G. Nietlispach F. et al.Acute kidney injury following transcatheter aortic valve implantation: predictive factors, prognostic value, and comparison with surgical aortic valve replacement.Eur Heart J. 2010; 31: 865-874Crossref PubMed Scopus (362) Google Scholar]. Several definitions of AKI have been proposed, and the adopted measurements include absolute creatinine value, absolute or percentage changes in serum creatinine (sCr) or estimated glomerular filtration values, and reduction in urine output [1Chertow G.M. Lazarus J.M. Christiansen C.L. et al.Preoperative renal risk stratification.Circulation. 1997; 95: 878-884Crossref PubMed Scopus (666) Google Scholar, 2Chertow G.M. Burdick E. Honour M. Bonventre J.V. Bates D.W. Acute kidney injury, mortality, length of stay, and costs in hospitalized patients.J Am Soc Nephrol. 2005; 16: 3365-3370Crossref PubMed Scopus (2549) Google Scholar, 3Karkouti K. Wijeysundera D.N. Yau T.M. et al.Acute kidney injury after cardiac surgery: focus on modifiable risk factors.Circulation. 2009; 119: 495-502Crossref PubMed Scopus (547) Google Scholar, 4Wijeysundera D.N. Karkouti K. Dupuis J.Y. et al.Derivation and validation of a simplified predictive index for renal replacement therapy after cardiac surgery.JAMA. 2007; 297: 1801-1809Crossref PubMed Scopus (328) Google Scholar, 5Thakar C.V. Arrigain S. Worley S. Yared J.P. Paganini E.P. A clinical score to predict acute renal failure after cardiac surgery.J Am Soc Nephrol. 2005; 16: 162-168Crossref PubMed Scopus (769) Google Scholar, 6Mehta R.H. Grab J.D. O'Brien S.M. et al.Bedside tool for predicting the risk of postoperative dialysis in patients undergoing cardiac surgery.Circulation. 2006; 114: 2208-2216Crossref PubMed Scopus (422) Google Scholar, 7Palomba H. de Castro I. Neto A.L. Lage S. Yu L. Acute kidney injury prediction following elective cardiac surgery: AKICS score.Kidney Int. 2007; 72: 624-631Crossref PubMed Scopus (253) Google Scholar, 8Brown J.R. Cochran R.P. Leavitt B.J. et al.Multivariable prediction of renal insufficiency developing after cardiac surgery.Circulation. 2007; 116: I139-I143Crossref PubMed Scopus (123) Google Scholar, 9Coca S.G. Yusuf B. Shlipak M.G. Garg A.X. Parikh C.R. Long-term risk of mortality and other adverse outcomes after acute kidney injury: a systematic review and meta-analysis.Am J Kidney Dis. 2009; 53: 961-973Abstract Full Text Full Text PDF PubMed Scopus (835) Google Scholar, 10Aronson S. Fontes M.L. Miao Y. Mangano D.T. Risk index for perioperative renal dysfunction/failure: critical dependence on pulse pressure hypertension.Circulation. 2007; 115: 733-742Crossref PubMed Scopus (183) Google Scholar, 11Brown J.R. Kramer R.S. Coca S.G. Parikh C.R. Duration of acute kidney injury impacts long-term survival after cardiac surgery.Ann Thorac Surg. 2010; 90: 1142-1148Abstract Full Text Full Text PDF PubMed Scopus (250) Google Scholar, 12Arnaoutakis G.J. Bihorac A. Martin T.D. et al.RIFLE criteria for acute kidney injury in aortic arch surgery.J Thorac Cardiovasc Surg. 2007; 134: 1554-1560Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar, 13Hobson C.E. Yavas S. Segal M.S. et al.Acute kidney injury is associated with increased long-term mortality after cardiothoracic surgery.Circulation. 2009; 119: 2444-2453Crossref PubMed Scopus (718) Google Scholar, 14Mangano C.M. Diamondstone L.S. Ramsay J.G. Aggarwal A. Herskowitz A. Mangano D.T. Renal dysfunction after myocardial revascularization: risk factors, adverse outcomes, and hospital resource utilization The Multicenter Study of Perioperative Ischemia Research Group.Ann Intern Med. 1998; 128: 194-203Crossref PubMed Scopus (931) Google Scholar, 15Rosner M.H. Okusa M.D. Acute kidney injury associated with cardiac surgery.Clin J Am Soc Nephrol. 2006; 1: 19-32Crossref PubMed Scopus (828) Google Scholar]. Common definitions consider a 50% or greater rise in sCr from baseline, rise in sCr more than 1 mg/dL above baseline, or an increase of at least 25% with a peak greater than 2 mg/dL [3Karkouti K. Wijeysundera D.N. Yau T.M. et al.Acute kidney injury after cardiac surgery: focus on modifiable risk factors.Circulation. 2009; 119: 495-502Crossref PubMed Scopus (547) Google Scholar, 9Coca S.G. Yusuf B. Shlipak M.G. Garg A.X. Parikh C.R. Long-term risk of mortality and other adverse outcomes after acute kidney injury: a systematic review and meta-analysis.Am J Kidney Dis. 2009; 53: 961-973Abstract Full Text Full Text PDF PubMed Scopus (835) Google Scholar, 10Aronson S. Fontes M.L. Miao Y. Mangano D.T. Risk index for perioperative renal dysfunction/failure: critical dependence on pulse pressure hypertension.Circulation. 2007; 115: 733-742Crossref PubMed Scopus (183) Google Scholar, 12Arnaoutakis G.J. Bihorac A. Martin T.D. et al.RIFLE criteria for acute kidney injury in aortic arch surgery.J Thorac Cardiovasc Surg. 2007; 134: 1554-1560Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar, 13Hobson C.E. Yavas S. Segal M.S. et al.Acute kidney injury is associated with increased long-term mortality after cardiothoracic surgery.Circulation. 2009; 119: 2444-2453Crossref PubMed Scopus (718) Google Scholar, 18Brown J.R. Cochran R.P. MacKenzie T.A. et al.Long-term survival after cardiac surgery is predicted by estimated glomerular filtration rate.Ann Thorac Surg. 2008; 86: 4-11Abstract Full Text Full Text PDF PubMed Scopus (100) Google Scholar, 19Benedetto U. Sciarretta S. Roscitano A. et al.Preoperative angiotensin-converting enzyme inhibitors and acute kidney injury after coronary artery bypass grafting.Ann Thorac Surg. 2008; 86: 1160-1165Abstract Full Text Full Text PDF PubMed Scopus (94) Google Scholar]. Other studies considered AKI only when a deterioration in renal function requiring postoperative dialysis is documented [1Chertow G.M. Lazarus J.M. Christiansen C.L. et al.Preoperative renal risk stratification.Circulation. 1997; 95: 878-884Crossref PubMed Scopus (666) Google Scholar, 2Chertow G.M. Burdick E. Honour M. Bonventre J.V. Bates D.W. Acute kidney injury, mortality, length of stay, and costs in hospitalized patients.J Am Soc Nephrol. 2005; 16: 3365-3370Crossref PubMed Scopus (2549) Google Scholar, 4Wijeysundera D.N. Karkouti K. Dupuis J.Y. et al.Derivation and validation of a simplified predictive index for renal replacement therapy after cardiac surgery.JAMA. 2007; 297: 1801-1809Crossref PubMed Scopus (328) Google Scholar, 5Thakar C.V. Arrigain S. Worley S. Yared J.P. Paganini E.P. A clinical score to predict acute renal failure after cardiac surgery.J Am Soc Nephrol. 2005; 16: 162-168Crossref PubMed Scopus (769) Google Scholar, 6Mehta R.H. Grab J.D. O'Brien S.M. et al.Bedside tool for predicting the risk of postoperative dialysis in patients undergoing cardiac surgery.Circulation. 2006; 114: 2208-2216Crossref PubMed Scopus (422) Google Scholar, 15Rosner M.H. Okusa M.D. Acute kidney injury associated with cardiac surgery.Clin J Am Soc Nephrol. 2006; 1: 19-32Crossref PubMed Scopus (828) Google Scholar]. New classification criteria have been recently proposed because of the wide variation in AKI definitions with a difficult result comparison across studies and populations [20Bellomo R. Ronco C. Kellum J.A. Mehta R.L. Palevsky P. Acute renal failure—definition, outcome measures, animal models, fluid therapy and information technology needs: the Second International Consensus Conference of the Acute Dialysis Quality Initiative (ADQI) Group.Crit Care. 2004; 8: R204-R212Crossref PubMed Google Scholar, 21Mehta R.L. Kellum J.A. Shah S.V. et al.Acute Kidney Injury Network: report of an initiative to improve outcomes in acute kidney injury.Crit Care. 2007; 11: R31Crossref PubMed Scopus (5301) Google Scholar]. The RIFLE (an acronym for risk, injury, failure, loss, end-stage kidney disease) criteria and the Acute Kidney Injury Network (AKIN) criteria have emerged as diagnostic tools for monitoring the severity and progression of postoperative AKI, and for having accurately characterized the entire spectrum of postoperative renal dysfunction (Table 1) [20Bellomo R. Ronco C. Kellum J.A. Mehta R.L. Palevsky P. Acute renal failure—definition, outcome measures, animal models, fluid therapy and information technology needs: the Second International Consensus Conference of the Acute Dialysis Quality Initiative (ADQI) Group.Crit Care. 2004; 8: R204-R212Crossref PubMed Google Scholar, 21Mehta R.L. Kellum J.A. Shah S.V. et al.Acute Kidney Injury Network: report of an initiative to improve outcomes in acute kidney injury.Crit Care. 2007; 11: R31Crossref PubMed Scopus (5301) Google Scholar]. The RIFLE classification defines three grades of severity (risk, injury, and failure) and two outcome classes (loss of kidney function and end-stage kidney disease) [20Bellomo R. Ronco C. Kellum J.A. Mehta R.L. Palevsky P. Acute renal failure—definition, outcome measures, animal models, fluid therapy and information technology needs: the Second International Consensus Conference of the Acute Dialysis Quality Initiative (ADQI) Group.Crit Care. 2004; 8: R204-R212Crossref PubMed Google Scholar]. Similarly, the AKIN system defines three progressive AKI stages, without outcome classes [21Mehta R.L. Kellum J.A. Shah S.V. et al.Acute Kidney Injury Network: report of an initiative to improve outcomes in acute kidney injury.Crit Care. 2007; 11: R31Crossref PubMed Scopus (5301) Google Scholar]. Although both systems are valuable methods to evaluate AKI, the favorite classification has not been identified yet [22Go A.S. Parikh C.R. Ikizler T.A. et al.The Assessment, Serial Evaluation, and Subsequent Sequelae of Acute Kidney Injury (ASSESS-AKI) study: design and methods.BMC Nephrol. 2010; 11: 22Crossref PubMed Scopus (119) Google Scholar]. In addition, in both classifications AKI etiology, duration of sCr elevation, and recovery of renal dysfunction are not considered [11Brown J.R. Kramer R.S. Coca S.G. Parikh C.R. Duration of acute kidney injury impacts long-term survival after cardiac surgery.Ann Thorac Surg. 2010; 90: 1142-1148Abstract Full Text Full Text PDF PubMed Scopus (250) Google Scholar, 23Coca S.G. King J.T. Rosenthal R.A. Perkal M.F. Parikh C.R. The duration of postoperative acute kidney injury is an additional parameter predicting long-term survival in diabetic veterans.Kidney Int. 2010; 78: 926-933Crossref PubMed Scopus (162) Google Scholar].Table 1Classification Systems for Acute Kidney Injury RIFLE Classification Criteria [20Bellomo R. Ronco C. Kellum J.A. Mehta R.L. Palevsky P. Acute renal failure—definition, outcome measures, animal models, fluid therapy and information technology needs: the Second International Consensus Conference of the Acute Dialysis Quality Initiative (ADQI) Group.Crit Care. 2004; 8: R204-R212Crossref PubMed Google Scholar]aWhen the baseline serum creatinine is not available, and there is no history of chronic kidney disease, creatinine is calculated assuming a glomerular filtration rate (GFR) of 75 mL · min−1 · 1.73 m−2.ClassGFR CriteriaUrinary Output CriteriaRisksCr increase × 1.5 or GFR decrease >25% 50% 75% or sCr ≥4 mg/dL with an acute rise >0.5 mg/dL 4 weeksEnd-stage renal diseaseEnd-stage renal disease >3 monthsAKIN Classification Criteria [21Mehta R.L. Kellum J.A. Shah S.V. et al.Acute Kidney Injury Network: report of an initiative to improve outcomes in acute kidney injury.Crit Care. 2007; 11: R31Crossref PubMed Scopus (5301) Google Scholar]bThe Acute Kidney Injury Network (AKIN) classification is defined as an abrupt reduction in kidney function, requiring at least two creatinine values within 48 hours.ClassessCr CriteriaUrinary Output Criteria1sCr increase × 1.5 or sCr increase >0.3 mg/dL from baseline 6 hours2sCr increase × 2 from baseline 12 hours3cPatients receiving renal replacement therapy are classified as stage 3.sCr increase × 3 or sCr increase >4 mg/dL with an acute increase >0.5 mg/dL 24 hours, or anuria × 12 hoursRIFLE = risk, injury, failure, loss of kidney function, and end-stage kidney disease; sCr = serum creatinine.a When the baseline serum creatinine is not available, and there is no history of chronic kidney disease, creatinine is calculated assuming a glomerular filtration rate (GFR) of 75 mL · min−1 · 1.73 m−2.b The Acute Kidney Injury Network (AKIN) classification is defined as an abrupt reduction in kidney function, requiring at least two creatinine values within 48 hours.c Patients receiving renal replacement therapy are classified as stage 3. Open table in a new tab RIFLE = risk, injury, failure, loss of kidney function, and end-stage kidney disease; sCr = serum creatinine. Finally, the new equation of the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) to estimate GFR has been proposed, being more accurate than the Modification of Diet in Renal Disease (MDRD) study equation, which is limited for the systematic underestimation of measured GFR at higher values [24Levey A.S. Stevens L.A. Schmid C.H. et al.A new equation to estimate glomerular filtration rate.Ann Intern Med. 2009; 150: 604-612Crossref PubMed Scopus (16513) Google Scholar, 25Stevens L.A. Coresh J. Feldman H.I. et al.Evaluation of the modification of diet in renal disease study equation in a large diverse population.J Am Soc Nephrol. 2007; 18: 2749-2757Crossref PubMed Scopus (472) Google Scholar]. Postoperative AKI is characterized by a progressive worsening course with different phases, the early one being characterized by a vasomotor nephropathy with alterations in vasoreactivity and renal perfusion [26Sutton T.A. Fisher C.J. Molitoris B.A. Microvascular endothelial injury and dysfunction during ischemic acute renal failure.Kidney Int. 2002; 62: 1539-1549Crossref PubMed Scopus (453) Google Scholar, 27Okusa M.D. The inflammatory cascade in acute ischemic renal failure.Nephron. 2002; 90: 133-138Crossref PubMed Scopus (199) Google Scholar]. The unavoidable consequence is prerenal azotemia, cellular adenosine triphosphate depletion, and oxidative injury, all leading to activation of bone-marrow derived and endothelial cells with a subsequent proinflammatory state [26Sutton T.A. Fisher C.J. Molitoris B.A. Microvascular endothelial injury and dysfunction during ischemic acute renal failure.Kidney Int. 2002; 62: 1539-1549Crossref PubMed Scopus (453) Google Scholar, 27Okusa M.D. The inflammatory cascade in acute ischemic renal failure.Nephron. 2002; 90: 133-138Crossref PubMed Scopus (199) Google Scholar]. Then, inflammatory cells adhere to activated endothelium in the peritubular capillaries of the outer medulla, with medullary congestion and hypoxic injury to the proximal tubule [26Sutton T.A. Fisher C.J. Molitoris B.A. Microvascular endothelial injury and dysfunction during ischemic acute renal failure.Kidney Int. 2002; 62: 1539-1549Crossref PubMed Scopus (453) Google Scholar, 27Okusa M.D. The inflammatory cascade in acute ischemic renal failure.Nephron. 2002; 90: 133-138Crossref PubMed Scopus (199) Google Scholar]. Proliferation of tubule cells and redifferentiation are subsequently followed by functional reconstitution. The typical lesion observed in a patient affected by postoperative AKI is acute tubular necrosis, with granular casts in the urine [26Sutton T.A. Fisher C.J. Molitoris B.A. Microvascular endothelial injury and dysfunction during ischemic acute renal failure.Kidney Int. 2002; 62: 1539-1549Cro
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