Acute Kidney Injury Severity and Long-Term Readmission and Mortality After Cardiac Surgery

Ann Thorac Surg. 2016 Nov;102(5):1482-1489. doi: 10.1016/j.athoracsur.2016.04.020. Epub 2016 Jun 17.


Background: Acute kidney injury (AKI) is a common complication after cardiac surgery. While AKI severity is known to be associated with increased risk of short-term outcomes, its long-term impact is less well understood.

Methods: Adult patients undergoing isolated coronary artery bypass graft surgery at eight centers were enrolled into the Northern New England biomarker registry (n = 1,610). Patients were excluded if they had renal failure (n = 15) or died during index admission (n = 38). Severity of AKI was defined using the Acute Kidney Injury Network (AKIN). We linked our cohort to national Medicare and state all-payer claims to ascertain readmissions and to the National Death Index to ascertain survival. Kaplan-Meier and multivariate Cox proportional hazards modeling was conducted for time to readmission and death over 5 years.

Results: Within 5 years, 513 patients (33.8%) had AKI with AKIN stage 1 (29.9%) and stage 2 to 3 (3.9%). There were 620 readmissions (39.9%) and 370 deaths (23.8%). After adjustment, stage 1 AKI patients had a 31% increased risk of readmission (95% confidence interval [CI]: 1.10 to 1.57), whereas stage 2 or 3 patients had a 98% increased risk (95% CI: 1.41 to 2.78) compared with patients having no AKI. Relative to patients without AKI, stage 1 patients had a 56% increased risk of mortality (95% CI: 1.14 to 2.13), whereas stage 2 or 3 patients had a 3.5 times higher risk (95% CI: 2.16 to 5.60).

Conclusions: Severity of AKI using the AKIN stage criteria is associated with a significantly increased risk of 5-year readmission and mortality. Our findings suggest that efforts to reduce AKI in the perioperative period may have a significant long-term impact on patients and payers in reducing mortality and health care utilization.

MeSH terms

  • Acute Kidney Injury / blood
  • Acute Kidney Injury / epidemiology*
  • Acute Kidney Injury / etiology
  • Acute Kidney Injury / mortality
  • Aged
  • Cause of Death
  • Coronary Artery Bypass
  • Creatinine / blood
  • Databases, Factual
  • Female
  • Humans
  • Kaplan-Meier Estimate
  • Male
  • Middle Aged
  • New England / epidemiology
  • Patient Readmission / statistics & numerical data*
  • Postoperative Complications / epidemiology*
  • Postoperative Complications / etiology
  • Postoperative Complications / mortality
  • Proportional Hazards Models
  • Retrospective Studies
  • Risk
  • Risk Factors
  • Severity of Illness Index


  • Creatinine