title: Impact of perioperative acute kidney injury as a severity index for thirty-day readmission after cardiac surgery.
abstract: BACKGROUND
  Of patients undergoing cardiac surgery in the United States, 15% to 20% are re-hospitalized within 30 days. Current models to predict readmission have not evaluated the association between severity of postoperative acute kidney injury (AKI) and 30-day readmissions.
  
  
  METHODS
  We collected data from 2,209 consecutive patients who underwent either coronary artery bypass or valve surgery at 7 member hospitals of the Northern New England Cardiovascular Disease Study Group Cardiac Surgery Registry between July 2008 and December 2010. Administrative data at each hospital were searched to identify all patients readmitted to the index hospital within 30 days of discharge. We defined AKI stages by the AKI Network definition of 0.3 or 50% increase (stage 1), twofold increase (stage 2), and a threefold or 0.5 increase if the baseline serum creatinine was at least 4.0 (mg/dL) or new dialysis (stage 3). We evaluate the association between stages of AKI and 30-day readmission using multivariate logistic regression.
  
  
  RESULTS
  There were 260 patients readmitted within 30 days (12.1%). The median time to readmission was 9 (interquartile range, 4 to 16) days. Patients not developing AKI after cardiac surgery had a 30-day readmission rate of 9.3% compared with patients developing AKI stage 1 (16.1%), AKI stage 2 (21.8%), and AKI stage 3 (28.6%, p < 0.001). Adjusted odds ratios for AKI stage 1 (1.81; 1.35, 2.44), stage 2 (2.39; 1.38, 4.14), and stage 3 (3.47; 1.85 to 6.50). Models to predict readmission were significantly improved with the addition of AKI stage (c-statistic 0.65, p = 0.001) and net reclassification rate of 14.6% (95% confidence interval: 5.05% to 24.14%, p = 0.003).
  
  
  CONCLUSIONS
  In addition to more traditional patient characteristics, the severity of postoperative AKI should be used when assessing a patient's risk for readmission.
authors.affiliation: Departments of Medicine Section of Cardiology and Community and Family Medicine, The Dartmouth Institute for Health Policy and Clinical Practice, and Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire. Electronic address: jbrown@dartmouth.edu.
authors.forename: Jeremiah R
authors.initials: JR
authors.lastname: Brown
authors.affiliation: Program of Applied Translational Research, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
authors.forename: Chirag R
authors.initials: CR
authors.lastname: Parikh
authors.affiliation: Departments of Medicine Section of Cardiology and Community and Family Medicine, The Dartmouth Institute for Health Policy and Clinical Practice, and Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire.
authors.forename: Cathy S
authors.initials: CS
authors.lastname: Ross
authors.affiliation: Department of Surgery, Maine Medical Center, Portland, Maine.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Kramer
authors.affiliation: Departments of Medicine Section of Cardiology and Community and Family Medicine, The Dartmouth Institute for Health Policy and Clinical Practice, and Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire.
authors.forename: Patrick C
authors.initials: PC
authors.lastname: Magnus
authors.affiliation: Department of Surgery, Concord Hospital, Concord, New Hampshire.
authors.forename: Kristine
authors.initials: K
authors.lastname: Chaisson
authors.affiliation: Department of Surgery, Concord Hospital, Concord, New Hampshire.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Boss
authors.affiliation: Department of Surgery, Portsmouth Regional Hospital, Portsmouth, New Hampshire.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Helm
authors.affiliation: Central Maine Heart and Vascular Center, Central Maine Medical Center, Lewiston, Maine.
authors.forename: Susan R
authors.initials: SR
authors.lastname: Horton
authors.affiliation: Department of Surgery, Eastern Maine Medical Center, Bangor, Maine.
authors.forename: Patricia
authors.initials: P
authors.lastname: Hofmaster
authors.affiliation: Department of Surgery, Catholic Medical Center, Manchester, New Hampshire.
authors.forename: Helen
authors.initials: H
authors.lastname: Desaulniers
authors.affiliation: Department of Surgery, Catholic Medical Center, Manchester, New Hampshire.
authors.forename: Pamela
authors.initials: P
authors.lastname: Blajda
authors.affiliation: Department of Surgery, Catholic Medical Center, Manchester, New Hampshire.
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Westbrook
authors.affiliation: Department of Surgery, Portsmouth Regional Hospital, Portsmouth, New Hampshire.
authors.forename: Dennis
authors.initials: D
authors.lastname: Duquette
authors.affiliation: Central Maine Heart and Vascular Center, Central Maine Medical Center, Lewiston, Maine.
authors.forename: Kelly
authors.initials: K
authors.lastname: LeBlond
authors.affiliation: Department of Surgery, Maine Medical Center, Portland, Maine.
authors.forename: Reed D
authors.initials: RD
authors.lastname: Quinn
authors.affiliation: Department of Surgery, Concord Hospital, Concord, New Hampshire.
authors.forename: Cheryl
authors.initials: C
authors.lastname: Jones
authors.affiliation: Department of Surgery, Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire.
authors.forename: Anthony W
authors.initials: AW
authors.lastname: DiScipio
authors.affiliation: Departments of Medicine Section of Cardiology and Community and Family Medicine, The Dartmouth Institute for Health Policy and Clinical Practice, and Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire.
authors.forename: David J
authors.initials: DJ
authors.lastname: Malenka
mesh_terms: D058186:Acute Kidney Injury / Q000175:diagnosis* / Q000209:etiology / Q000401:mortality / Q000628:therapy; D000368:Aged; D006348:Cardiac Surgical Procedures / Q000009:adverse effects* / Q000379:methods* / Q000401:mortality; D016001:Confidence Intervals; D001026:Coronary Artery Bypass / Q000009:adverse effects / Q000379:methods / Q000401:mortality; D005260:Female; D019918:Heart Valve Prosthesis Implantation / Q000009:adverse effects / Q000379:methods / Q000401:mortality; D017052:Hospital Mortality; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D010359:Patient Readmission / Q000706:statistics & numerical data*; D019990:Perioperative Care; D011183:Postoperative Complications / Q000175:diagnosis / Q000401:mortality / Q000628:therapy; D011237:Predictive Value of Tests; D012042:Registries; D012189:Retrospective Studies; D018570:Risk Assessment; D012720:Severity of Illness Index; D015996:Survival Rate; D013997:Time Factors; D006113:United Kingdom
keywords: 4