The association of acute kidney injury in the critically ill and postdischarge outcomes: a cohort study*

Abstract

Objective: Hospital readmissions contribute significantly to the cost of inpatient care and are targeted as a marker for quality of care. Little is known about risk factors associated with hospital readmission in survivors of critical illness. We hypothesized that acute kidney injury in patients who survived critical care would be associated with increased risk of 30-day postdischarge hospital readmission, postdischarge mortality, and progression to end-stage renal disease.

Design: Two center observational cohort study.

Setting: Medical and surgical ICUs at the Brigham and Women's Hospital and the Massachusetts General Hospital in Boston, Massachusetts.

Patients: We studied 62,096 patients, 18 years old and older, who received critical care between 1997 and 2012 and survived hospitalization.

Interventions: None

Measurements and main results: : All data was obtained from the Research Patient Data Registry at Partners HealthCare. The exposure of interest was acute kidney injury defined as meeting Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease Risk, Injury or Failure criteria occurring 3 days prior to 7 days after critical care initiation. The primary outcome was hospital readmission in the 30 days following hospital discharge. The secondary outcome was mortality in the 30 days following hospital discharge. Adjusted odds ratios were estimated by multivariable logistic regression models with inclusion of covariate terms thought to plausibly interact with both acute kidney injury and readmission status. Adjustment included age, race (white vs nonwhite), gender, Deyo-Charlson Index, patient type (medical vs surgical) and sepsis. Additionally, long-term progression to End Stage Renal Disease in patients with acute kidney injury was analyzed with a risk-adjusted Cox proportional hazards regression model. The absolute risk of 30-day readmission was 12.3%, 19.0%, 21.2%, and 21.1% in patients with No Acute Kidney Injury, Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease class Risk, Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease class Injury, and Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease class Failure, respectively. In patients who received critical care and survived hospitalization, acute kidney injury was a robust predictor of hospital readmission and post-discharge mortality and remained so following multivariable adjustment. The odds of 30-day post-discharge hospital readmission in patients with Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease class Risk, Injury, or Failure fully adjusted were 1.44 (95% CI, 1.25-1.66), 1.98 (95% CI, 1.66-2.36), and 1.55 (95% CI, 1.26-1.91) respectively, relative to patients without acute kidney injury. Further, the odds of 30-day post-discharge mortality in patients with Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease class Risk, Injury, or Failure fully adjusted per our primary analysis were 1.39 (95% CI, 1.28-1.51), 1.46 (95% CI, 1.30-1.64), and 1.42 (95% CI, 1.26-1.61) respectively, relative to patients without acute kidney injury. The addition of the propensity score to the multivariable model did not change the point estimates significantly. Finally, taking into account age, gender, race, Deyo-Charlson Index, and patient type, we observed a relationship between acute kidney injury and development of end-stage renal disease. Patients with Risk, Injury, Failure, Loss of kidney function, and End-stage kidney disease class Risk, Injury, Failure experienced a significantly higher risk of end-stage renal disease during follow-up than patients without acute kidney injury (hazard ratio, 2.03; 95% CI, 1.56-2.65; hazard ratio, 3.99; 95% CI, 3.04-5.23; hazard ratio, 10.40; 95% CI, 8.54-12.69, respectively).

Conclusions: Patients who suffer acute kidney injury are among a high-risk group of ICU survivors for adverse outcomes. In patients treated with critical care who survive hospitalization, acute kidney injury is a robust predictor of subsequent unplanned hospital readmission. In critical illness survivors, acute kidney injury is also associated with the odds of 30-day postdischarge mortality and the risk of subsequent end-stage renal disease.